CN110707925A

CN110707925A - Zero-crossing detection circuit, zero-crossing detection method and switching power supply circuit

Info

Publication number: CN110707925A
Application number: CN201910895359.2A
Authority: CN
Inventors: 姚云龙
Original assignee: Hangzhou Silan Microelectronics Co Ltd
Current assignee: Hangzhou Silan Microelectronics Co Ltd
Priority date: 2019-09-20
Filing date: 2019-09-20
Publication date: 2020-01-17

Abstract

The application discloses a zero-crossing detection circuit, a zero-crossing detection method and a switching power supply circuit. The zero-crossing detection circuit is used for providing a zero-crossing indication signal according to a signal to be detected, the signal to be detected responds to an inductive current provided by an inductor, the inductor is charged when the power switch tube is conducted, and discharges electricity to realize follow current when the power switch tube is turned off, and the zero-crossing detection circuit comprises: the detection unit is used for judging whether the inductive current is reduced to zero or not according to the zero-crossing reference value and the signal to be detected and providing a zero-crossing indication signal representing a judgment result; and the adjusting signal generating unit is used for detecting the follow current time of the inductor and adjusting the zero-crossing reference value according to the follow current time. The zero-crossing detection function can be optimized under the condition that the output voltages of the switching power supply circuit are different, so that the abnormity such as interference and detection failure can be prevented.

Description

Zero-crossing detection circuit, zero-crossing detection method and switching power supply circuit

Technical Field

The present invention relates to the field of electronic circuit technology, and more particularly, to a zero-crossing detection circuit, a zero-crossing detection method, and a switching power supply circuit.

Background

In some circuits, some functions are often implemented by using the characteristic that inductance hinders current change. For example, in a switching power supply circuit, an inductor may be charged during a conduction phase of a power driving transistor to make a current flowing through the inductor reach a peak value, and a load capacitor may be discharged during a shutdown phase of the power driving transistor by using the inductor, so that an output voltage across the load capacitor may be maintained within an allowable range. Therefore, whether the current flowing through the inductor crosses zero or not is detected in the turn-off stage of the power driving tube, the output voltage at two ends of the load capacitor and the current flowing through the inductor are estimated by combining the topological structure of the circuit, and the inductance current zero crossing detection can also be used for indicating whether the power driving tube needs to be conducted to recharge the inductor or not and/or indicating the overvoltage condition of the output voltage to realize overvoltage protection.

In a conventional inductive current zero-crossing detection scheme, an auxiliary winding, a capacitor coupling or a voltage division network is generally adopted to obtain a signal to be detected in response to an inductive current, and a zero-crossing comparator is used to compare the signal to be detected with a fixed zero-crossing reference value so as to obtain a detection result for representing whether the inductive current crosses zero.

The problems of the conventional scheme are as follows: if the sensitivity of the zero-crossing detection is set to be higher, when the output voltage at two ends of the load capacitor is higher, the change amplitude of the inductive current is larger, so that burrs are easy to appear on a signal to be detected, and the output signal of the zero-crossing comparator is mistakenly turned over under the condition that the sensitivity of the zero-crossing detection is higher, so that the zero-crossing detection result is mistaken, overvoltage protection is easily triggered, and the anti-interference capability of the zero-crossing detection is weaker; if the sensitivity of the zero-crossing detection is set to be low, the output signal of the zero-crossing comparator is turned over when the difference between the signal to be detected and the zero-crossing reference value is large, however, when the output voltage at the two ends of the load capacitor is low, the change amplitude of the inductive current is small, the signal to be detected is difficult to generate a large difference value with the zero-crossing reference value, and therefore, whether the inductive current crosses zero or not can not be detected, namely, the zero-crossing detection function is abnormal.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a zero-cross detection circuit, a zero-cross detection method, and a switching power supply circuit, which can adjust a zero-cross reference value according to a freewheeling time of an inductor current to adjust a sensitivity of the zero-cross detection circuit. Because the freewheeling time of the inductive current is related to the amplitude of the output voltage, the technical scheme provided by the invention can adaptively adjust the sensitivity of the zero-crossing detection circuit under the condition of different output voltages so as to prevent glitch interference and avoid abnormal work caused by the fact that zero crossing cannot be detected.

According to a first aspect of the present invention, there is provided a zero-crossing detection circuit for providing a zero-crossing indication signal according to a signal to be detected, the signal to be detected being responsive to an inductor current provided by an inductor, the inductor being charged when a power switch tube is turned on and discharged to realize a follow current when the power switch tube is turned off, the power switch tube being configured to convert an input voltage to an output voltage, the zero-crossing detection circuit comprising: the detection unit is used for judging whether the inductive current is reduced to zero or not according to the zero-crossing reference value and the signal to be detected and providing the zero-crossing indication signal representing the judgment result; and the adjusting signal generating unit is used for detecting the follow current time of the inductor and adjusting the zero-crossing reference value according to the follow current time.

Optionally, when the freewheel time detected by the adjustment signal generating unit is short, the output voltage is high, the adjustment signal generating unit adjusts the zero-crossing reference value so that the sensitivity of the zero-crossing detection circuit is adjusted to be low, and when the freewheel time detected by the adjustment signal generating unit is long, the output voltage is low, and the adjustment signal generating unit adjusts the zero-crossing reference value so that the sensitivity of the zero-crossing detection circuit is adjusted to be high.

Optionally, the adjustment signal generation unit continuously or stepwise decreases the zero-crossing reference value as the freewheel time increases.

Optionally, with an increase of the freewheel time, the adjustment signal generating unit decreases the zero-crossing reference value in a stepwise manner, when the freewheel time at different times is in a same one of a plurality of preset time intervals, the corresponding zero-crossing reference value is the same, and a length of each time interval is a fixed value, or is positively correlated with a peak current of the inductor current corresponding to the time interval, or is negatively correlated with an amplitude of the output voltage corresponding to the time interval.

Optionally, the adjusting signal generating unit starts timing from an initial value when the power switching tube is turned off to obtain a timing signal, and adjusts the zero-crossing reference value according to the timing signal, wherein when the zero-crossing indication signal indicates that the inductor current has decreased to zero, the adjusting signal generating unit stops timing, and the timing signal indicates a freewheeling time that the inductor has elapsed since the power switching tube was turned off.

Optionally, the adjusting signal generating unit adjusts the zero-crossing reference value according to a comparison result between the timing signal and at least one reference time value, so that the zero-crossing reference value decreases stepwise with an increase of the freewheel time.

Optionally, the detecting unit includes: the conversion module is used for converting the signal to be detected into resonance sampling voltage according to a conversion coefficient; the reference voltage generating module is used for generating a first reference voltage; and a comparison module, configured to provide the zero-crossing indication signal according to a comparison result between the resonant sampling voltage and the first reference voltage, wherein the zero-crossing reference value is positively correlated to the first reference voltage and negatively correlated to the conversion coefficient.

Optionally, the adjusting signal generating unit includes: a first current source providing a charging current; a first capacitor, a first end of which starts receiving the charging current when the power driving tube is turned off to provide a timing voltage for representing the freewheeling time and is reset to an initial potential representing the initial value when the zero-crossing indication signal represents that the inductive current has dropped to zero, the adjusting unit adjusts the first reference voltage and/or the conversion coefficient according to the timing voltage or a digital signal corresponding to the timing voltage to adjust the zero-crossing reference value.

Optionally, the conversion module is coupled to the second end of the power driving tube to couple to the current output end of the inductor and obtain the signal to be detected.

Optionally, the conversion module includes a second capacitor and a first resistor connected in series between the second end of the power driving transistor and a reference ground in sequence, a node where the second capacitor is connected to the first resistor provides the resonant sampling voltage, and the conversion coefficient is positively related to a product of a capacitance value of the second capacitor and a resistance value of the first resistor.

Optionally, the adjustment signal generating unit provides a corresponding first adjustment signal according to the freewheel time, where a capacitance value of the second capacitor and/or a resistance value of the first resistor continuously increases or increases in a stepwise manner with an increase of the freewheel time under the control of the first adjustment signal.

Optionally, the conversion module includes a second resistor and a third resistor connected in series between the second end of the power driving transistor and a reference ground in sequence, a node where the second resistor and the third resistor are connected provides the resonant sampling voltage, and the conversion coefficient is negatively related to a ratio of resistance values of the second resistor and the third resistor.

Optionally, the adjustment signal generating unit provides a corresponding second adjustment signal according to the freewheel time, and the resistance values of the second resistor and/or the third resistor are controlled by the second adjustment signal, wherein under the action of the second adjustment signal, the ratio of the resistance values of the second resistor and the third resistor continuously decreases or decreases in a stepwise manner with the increase of the freewheel time.

Optionally, the adjustment signal generating unit provides a corresponding third adjustment signal according to the free-wheeling time, and the reference voltage generating module is controlled by the third adjustment signal to provide the variable first reference voltage, wherein the first reference voltage continuously decreases or stepwise decreases with an increase of the free-wheeling time.

Optionally, the conversion module is connected to the control end of the power driving tube to couple with the current output end of the inductor and obtain the signal to be detected.

Optionally, the conversion module includes: the enabling switch is alternatively conducted with the power driving tube; and the detection resistance unit and the enabling switch are connected in series between the control end of the power driving tube and a reference ground, the conversion coefficient is positively correlated with the resistance value of the detection resistance unit, and when the enabling switch is switched on, the control end of the power driving tube provides the resonance sampling voltage according to the signal to be detected under the coupling action of the control end of the power driving tube and the current output end of the inductor.

Optionally, the conversion module further includes a clamping element connected in parallel with the detection resistance unit, and when the power driving tube is turned off, the clamping element clamps the resonant sampling voltage, so that the resonant sampling voltage does not exceed a set threshold and the power driving tube cannot be turned on.

Optionally, the adjustment signal generating unit provides a corresponding fourth adjustment signal according to the freewheel time, and the resistance value of the detection resistor unit is controlled by the fourth adjustment signal, wherein the total resistance value of the detection resistor unit continuously increases or increases in a stepwise manner with the increase of the freewheel time.

Optionally, the detection resistor unit includes a plurality of first detection resistors and a plurality of first detection switches, a first end of each of the first detection resistors is connected to a reference ground through a corresponding one of the first detection switches, second ends of the plurality of first detection resistors are interconnected, the enable switch is connected in series between the first end of each of the first detection resistors and the reference ground, or between a common connection point of the second ends of the plurality of first detection resistors and the control end of the power driving transistor, and a plurality of sub-signals of the fourth adjustment signal respectively control on and off of each of the first detection switches, so as to adjust a total resistance value of the detection resistor unit.

Optionally, at the initial turn-on time of the enable switch, the plurality of first detection switches are all turned on under the control of the fourth adjustment signal, and as the freewheel time increases, the plurality of first detection switches are sequentially turned off by corresponding sub-signals of the fourth adjustment signal.

Optionally, the detection resistor includes a plurality of second detection resistors and a plurality of second detection switches, the plurality of second detection resistors are sequentially connected in series between the control end of the power driving tube and a reference ground, every two connection nodes between the second detection resistors are respectively connected to the reference ground through a corresponding one of the second detection switches, the enable switch is connected in series between the plurality of second detection resistors and the control end of the power driving tube or between the plurality of second detection resistors and the reference ground, and the plurality of sub-signals of the fourth adjustment signal respectively control on and off of each of the second detection switches to adjust the resistance of the detection resistor.

Optionally, at the initial turn-on time of the enable switch, the plurality of second detection switches are all turned on under the control of the fourth adjustment signal, and as the freewheel time increases, the plurality of second detection switches are sequentially turned off by corresponding sub-signals of the fourth adjustment signal.

Optionally, the comparing module includes: and a positive phase input end of the first comparator receives the first reference voltage, a negative phase input end of the first comparator receives the resonance sampling voltage, and an output end of the first comparator provides the zero-crossing indication signal.

Optionally, the delay unit is further included, and is connected to the output end of the first comparator to filter out a narrow pulse having a pulse width smaller than a preset pulse width in the zero-crossing indication signal.

Optionally, the adjusting unit provides a fifth adjusting signal to the delay unit according to the follow current time to adjust the preset pulse width, so that the preset pulse width is inversely related to the follow current time.

According to a second aspect of the present invention, there is provided a switching power supply circuit comprising: a zero-crossing detection circuit as claimed in any one of the above; a load capacitor providing the output voltage; the control end of the power driving tube is controlled by a switch control signal; the inductor is used for providing an inductor current, and the inductor current flows to the current output end of the inductor through the current input end of the inductor; and the driving circuit provides the switch control signal according to the zero-crossing indication signal.

Optionally, the power driver further includes an auxiliary driving tube, the auxiliary driving tube is connected in series between the current output end of the inductor and the second end of the power driving tube, and the control end of the auxiliary driving tube receives a conduction level for conducting the auxiliary driving tube.

Optionally, the switching power supply circuit further includes: the sampling resistor is connected between the first end of the power driving tube and the reference ground in series; and the current detection circuit is coupled with the first end of the power driving tube to obtain a current sampling voltage, judges whether the inductive current reaches the current peak value according to the current sampling voltage and provides a peak value indicating signal representing a judgment result, wherein the driving circuit provides the switch control signal according to the zero-crossing indicating signal and the peak value indicating signal.

Optionally, the switching power supply circuit further includes an overvoltage detection circuit, configured to determine whether the output voltage exceeds an expected value according to the freewheeling time and the overvoltage reference value, and provide an overvoltage indication signal according to a determination result, where the overvoltage indication signal controls the driving circuit to adjust a duty ratio of the switching control signal, and/or controls the zero-crossing detection circuit to enable the zero-crossing detection circuit to adjust the zero-crossing reference value according to the overvoltage indication signal.

Optionally, when the overvoltage indication signal indicates that the output voltage is smaller than the expected value, the zero-crossing reference value is equal to a first preset value, and when the overvoltage indication signal indicates that the output voltage is greater than/equal to the expected value, the zero-crossing reference value is equal to a second preset value, where the first preset value is greater than the second preset value.

According to a third aspect of the present invention, there is also provided a zero-crossing detection method for providing a zero-crossing indication signal according to a signal to be detected, wherein the signal to be detected is responsive to an inductor current provided by an inductor, the inductor is charged when a power switch tube is turned on, and is discharged to realize a follow current when the power switch tube is turned off, and the power switch tube is used for converting an input voltage into an output voltage, the zero-crossing detection method comprising: judging whether the inductive current is reduced to zero or not according to a zero-crossing reference value and the signal to be detected, and providing a zero-crossing indication signal representing a judgment result; detecting a freewheel time of the inductor; and adjusting the zero-crossing reference value according to the freewheel time.

Optionally, when the detected freewheel time is short, the output voltage is high, the zero-crossing reference value is adjusted to lower the sensitivity of zero-crossing detection, and when the detected freewheel time is long, the output voltage is low, the zero-crossing reference value is adjusted to increase the sensitivity of zero-crossing detection.

Optionally, the step of adjusting the zero-crossing reference value includes: the zero-crossing reference value is adjusted continuously low or stepwise as the freewheel time increases.

Optionally, the zero-crossing reference value is adjusted down in a stepwise manner as the freewheeling time increases, when the freewheeling time at different times is in the same one of the preset time intervals, the corresponding zero-crossing reference value is the same, the length of each time interval is a fixed value, or the peak current of the inductive current corresponding to the time interval is positively correlated, or the amplitude of the output voltage corresponding to the time interval is negatively correlated, and the output voltage is provided by the power switching tube and the switching power supply circuit where the inductor is located.

Optionally, the step of detecting the freewheel time includes: starting timing from an initial value to obtain a timing signal when the power switch tube is turned off, wherein the timing signal represents the freewheeling time of the inductor from the time when the power switch tube is turned off; and stopping timing when the zero-crossing indication signal indicates that the inductor current has dropped to zero.

Optionally, the step of adjusting the zero-crossing reference value includes: adjusting the zero-crossing reference value in dependence on a comparison of the timing signal and at least one reference time value such that the zero-crossing reference value decreases stepwise with increasing freewheel time.

Optionally, the step of providing the zero-crossing indication signal includes: converting the signal to be detected into resonance sampling voltage according to a conversion coefficient; and providing the zero-crossing indication signal according to a comparison result of the resonant sampling voltage and a first reference voltage, wherein the zero-crossing reference value is positively correlated with the first reference voltage and negatively correlated with the conversion coefficient.

Optionally, the conversion factor increases continuously or in a stepwise manner as the freewheel time increases.

Optionally, the first reference voltage is continuously decreased or stepwise decreased with an increase in the freewheel time.

Optionally, the step of adjusting the zero-crossing reference value includes: when the power driving tube is turned off, starting to charge a first capacitor by using a charging current, so that a first end of the first capacitor provides a timing voltage for representing the freewheeling time; when the zero-crossing indication signal indicates that the inductor current has dropped to zero, the first terminal of the first capacitor is reset to an initial potential that indicates the initial value; and adjusting the first reference voltage and/or the conversion coefficient according to the timing voltage or a digital signal corresponding to the timing voltage so as to adjust the zero-crossing reference value.

Optionally, the second end of the power driving tube is coupled to the current output end of the inductor to provide the signal to be detected.

Optionally, the conversion coefficient is positively correlated to a time constant of a filter, an input end of the filter is coupled to the second end of the power driving tube, and an output end of the filter provides the resonant sampling voltage.

Optionally, the conversion coefficient is a voltage division coefficient of a voltage division resistance network, an input end of the voltage division resistance network is coupled with the second end of the power driving tube, and an output end of the voltage division resistance network provides the resonance sampling voltage.

Optionally, the control end of the power driving tube is coupled to the current output end of the inductor to provide the signal to be detected.

Optionally, the conversion coefficient is a total resistance value of a detection resistance unit, and the detection resistance unit is coupled between the current output end and a reference ground and provides the resonance sampling voltage related to the total resistance value under the action of the signal to be detected.

Optionally, the step of providing the zero-crossing indication signal includes: and delaying the zero-crossing indicating signal to filter out narrow pulses with pulse widths smaller than a preset pulse width in the zero-crossing indicating signal.

Optionally, the step of providing the zero-crossing indication signal further includes: and adjusting the preset pulse width according to the follow current time, so that the preset pulse width is inversely related to the follow current time.

According to the zero-crossing detection circuit, the zero-crossing detection method and the switching power supply circuit provided by the embodiment of the invention, the sensitivity of zero-crossing detection can be adjusted according to the freewheeling time of the inductive current, so that the zero-crossing detection circuit is suitable for applications with higher and lower output voltages of the switching power supply circuit, namely: when the detected follow current time is short, the representation output voltage is high, the zero-crossing detection function can be adjusted to enable the zero-crossing detection function to have low sensitivity, the low sensitivity can improve the anti-interference capability, and therefore the influence caused by interference such as burrs is weakened or eliminated; when the detected follow current time is increased, the representation output voltage is lower, the sensitivity of the zero-crossing detection function can be improved, the high sensitivity can ensure that the zero-crossing moment of the inductive current can be detected, and the condition that the zero-crossing detection function fails is avoided.

Therefore, the zero-crossing detection circuit, the zero-crossing detection method and the switching power supply circuit provided by the embodiment of the invention can adaptively complete zero-crossing detection under different output voltage amplitudes, so that the switching power supply circuit has strong anti-jamming capability and stable zero-crossing detection function, and is wide in application range.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings.

Fig. 1 shows a circuit schematic of a switching power supply circuit of an embodiment of the present invention.

Fig. 2 shows a circuit schematic of a switching power supply circuit according to another embodiment of the present invention.

Fig. 3 shows a schematic block diagram of one implementation of a controller in a first embodiment of the invention.

Fig. 4 shows a waveform diagram of a part of signals in the main circuit according to an embodiment of the present invention.

Fig. 5 shows a schematic diagram of the relationship between the zero-crossing reference value and the freewheel time in an embodiment of the invention.

Fig. 6a shows a schematic circuit diagram of one implementation of a zero crossing detection circuit of an embodiment of the present invention.

Fig. 6b shows a schematic circuit diagram of another implementation of a zero crossing detection circuit of an embodiment of the invention.

Fig. 7a to 7d show circuit schematic diagrams of various implementations of a conversion module according to an embodiment of the invention.

Fig. 8 shows a schematic waveform diagram of part of the signals in fig. 7 d.

Fig. 9 shows a schematic circuit diagram of an implementation of the delay unit shown in fig. 6 b.

Detailed Description

Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Like elements in the various figures are denoted by the same or similar reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale.

The present invention may be embodied in various forms, some examples of which are described below.

Fig. 1 shows a circuit schematic of a switching power supply circuit of a first embodiment of the present invention.

As shown in fig. 1, the switching power supply circuit 1000 includes a main circuit 1100 and a controller 1200. The switching power supply circuit 1000 of the present embodiment will be described below by taking a step-down structure as an example. However, the embodiments of the present invention are not limited thereto, and the basic idea of the present invention is also applicable to switching power supply circuits with other structures, such as a flyback structure, a boost structure, and the like.

1. Main circuit

As shown in fig. 1, the main circuit 1100 of the switching power supply circuit may include a power driving transistor M1, a diode D1, an inductor L1, a load capacitor Cout, and a sampling resistor Rcs.

The first end of the power driving tube M1 is connected with the first end of the sampling resistor Rcs, and the second end of the sampling resistor Rcs is grounded. The sampling resistor Rcs is connected in series with the power driving transistor M1, so that the sampling voltage Vcs provided by the first terminal of the sampling resistor Rcs can represent the current flowing through the power driving transistor M1.

The second terminal of the power driving transistor M1 is connected to the anode of the diode D1 and the first terminal (current output terminal) of the inductor L1 at the switch node LX, the cathode of the diode D1 is connected to the positive input terminal of the input voltage (receiving the input voltage Vin) and the first terminal of the load capacitor Cout, the second terminal of the inductor L1 is connected to the second terminal of the load capacitor Cout, and thus the voltage difference between the two terminals of the load capacitor Cout is equal to the output voltage Vout. The load capacitor Cout may be an equivalent capacitor provided by a subsequent circuit, or may be an independently arranged capacitor.

The power driving transistor M1 is, for example, an N-channel or P-channel fet. The present embodiment will be described by taking an N-channel fet as an example, where: the first terminal of the power driving transistor M1 is a source, the second terminal is a drain, and the control terminal is a gate.

As an alternative embodiment, as shown in fig. 2, the main circuit 1100 may further include an auxiliary driving transistor M2 connected in series between the first terminal of the power driving transistor M1 and the current output terminal of the inductor L1 (e.g., connected to the switch node LX), and the control terminal of the auxiliary driving transistor M2 receives the turn-on level. The auxiliary driving transistor M2 is, for example, an N-channel fet, and the conduction level is, for example, the supply voltage VCC. The main circuit 1100 shown in fig. 2 is substantially the same as the main circuit shown in fig. 1 except for the auxiliary drive tube M2, and the description of the same parts is omitted.

Further, fig. 4 shows a waveform diagram of a partial signal in the main circuit according to an embodiment of the present invention. As shown in fig. 4, in the on-phase of the power driving transistor M1 (e.g. corresponding to the high-level phase of the switch control signal GT), the inductor L1 accumulates energy so that the current flowing through the inductor L1 reaches the current peak at the off-time of the power driving transistor M1; in the turn-off stage of the power driving transistor (e.g. corresponding to the low stage of the switch control signal GT), the inductor L1 in the freewheeling state releases electric energy to charge the load capacitor, and the inductor current flowing through the inductor L1 continuously decreases; when the inductor current drops to 0, the inductor L1 ends the freewheeling state and enters the resonant state, at this time, the inductor current resonates due to the residual energy in the inductor L1, and the drain voltage VD and the gate voltage GT of the power driving transistor M1 also resonate due to the capacitive coupling; when the power drive transistor M1 is turned on again (e.g., at the bottom of the resonant valley), the inductor current rises again until the current peak is reached.

As shown in fig. 1 and fig. 2, if the voltage drop of the diode D1 is neglected, the time Tdis that the inductor current flowing through the inductor L1 drops from the peak value to 0 in the turn-off phase of the power driving transistor M1 is about:

Tdis＝L*Ipk/Vout

where L represents the inductance of inductor L1, Ipk represents the peak current flowing through inductor L1, and Vout represents the output voltage. It can be seen that the higher the output voltage Vout, the shorter the duration of the freewheeling state (hereinafter referred to as the freewheeling time) Tdis of the inductor can be detected, and thus the amplitude of the output voltage Vout can be estimated from the freewheeling time Tdis of the inductor.

At the end of the freewheeling state of the inductor, i.e. when the drain voltage of the power driver transistor M1 starts to resonate, the initial resonant amplitude corresponds to the output voltage Vout. Therefore, when the inductance L of the inductor L1 and the peak current value Ipk flowing through the inductor L1 are fixed, the higher the output voltage Vout provided by the switching power supply circuit is, the larger the corresponding initial resonance amplitude at the end of the freewheeling state is, and the shorter the freewheeling time Tdis can be detected; meanwhile, when the zero-cross detection is performed, the larger the resonance amplitude (for example, the amount of change in the drain voltage VD of the power driving transistor M1) is, the easier it is to detect the change in the current signal/voltage signal, and thus, the more accurately it is possible to detect whether the inductor current has reached 0.

2. Controller

As shown in fig. 1, the controller 1200 of the switching power supply circuit is configured to provide a switching control signal GT to the control terminal of the power driver M1. The controller 1200 may include: a zero-cross detection circuit 1210, a current detection circuit 1220, and a switch drive circuit 1230.

In the embodiment of the present invention, the controller 1200 may operate in an discontinuous conduction mode or a critical conduction mode. The discontinuous conduction mode is: after the inductor current provided by the inductor L1 is detected to be reduced to 0, the power driving tube M1 is switched from the off state to the on state after a period of time is delayed; the critical conduction mode is: when the current provided by the inductor L1 is detected to drop to 0, the power driving tube M1 is switched from the off state to the on state immediately. Both modes of operation require the zero crossing detection circuit 1210 to know whether the inductor current flowing through the inductor L1 crosses zero.

2.1 Current detection Circuit

The current detection circuit 1220 is connected to a first terminal of the sampling resistor Rcs to receive the sampling voltage Vcs and detect the sampling voltage Vcs to generate the peak indicator signal Vpkd. The current detection circuit 1220 determines whether the current flowing through the power driving transistor M1 reaches a set peak value by detecting the amplitude of the sampling voltage Vcs, for example, and provides a peak value indicating signal Vpkd according to the detection result. As an alternative embodiment, the current detection circuit 1220 may include a voltage comparator for comparing the sampled voltage Vcs with a voltage indicative of a set peak value, thereby outputting a peak indication signal Vpkd in response to the comparison result.

2.2 zero-crossing detection circuit

The zero-crossing detection circuit 1210 is coupled to the inductor L1 (e.g., connected to the drain or gate of the power driving transistor M1 to be coupled to the current output terminal/switching node LX of the inductor L1) to obtain a signal Vts to be detected, which can represent the inductor current flowing through the inductor L1, and is configured to provide a zero-crossing indication signal Vzcd according to the signal Vts to be detected and a zero-crossing reference value ZRef, which is used to represent whether the inductor current flowing through the inductor L1 has fallen to 0.

The operation principle of the zero-crossing detection circuit 1210 may be equivalent to, for example, the following process: when the signal Vts to be detected is less than the zero-crossing reference value ZRef, the zero-crossing detection circuit 1210 provides an effective zero-crossing indication signal Vzcd to indicate that the zero-crossing of the inductor current is detected; when the signal Vts to be detected is greater than/equal to the zero-crossing reference value ZRef, the zero-crossing detection circuit 1210 provides an invalid zero-crossing indication signal Vzcd ratio indicating that the inductor current does not cross zero. However, embodiments of the invention are not limited thereto.

When the zero-crossing indication signal Vzcd indicates that the current flowing through the inductor L1 has dropped to 0 (zero crossing), which indicates that the inductor L1 cannot continue to provide enough energy, the power driving transistor M1 needs to be turned on to increase the inductor current flowing through the inductor L1, and therefore the zero-crossing indication signal Vzcd can be used to determine whether the power driving transistor M1 needs to start to be turned on.

In some embodiments, as shown in fig. 1, the zero-crossing detection circuit 1210 may be coupled to the gate of the power driving transistor M1, that is, the signal to be detected Vts may be a signal provided by the gate of the power driving transistor M1, so that the zero-crossing detection circuit 1210 can determine whether the inductive current flowing through the inductor L1 has dropped to 0 by detecting the voltage change of the gate of the power driving transistor M1 under the coupling effect of the gate-drain parasitic capacitance during the turn-off phase of the power driving transistor M1, and provide a corresponding zero-crossing indication signal Vzcd; in other embodiments, the zero-crossing detection circuit 1210 may be coupled to the drain of the power driving transistor M1, that is, the signal to be detected Vts may be a drain voltage VD provided by the power driving transistor M1, so that the zero-crossing detection circuit 1210 can determine whether the inductor current flowing through the inductor L1 has reached 0 according to the drain voltage VD and provide a corresponding zero-crossing indication signal Vzcd.

In some embodiments, the output current and/or the output voltage Vout of the switching power supply circuit 1000 may also be calculated from the actual circuit topology and the zero crossing indication signal Vzcd.

The zero-cross detection circuit 1210 provided by the embodiment of the present invention starts timing from an initial value when the power driving transistor M1 is turned off (or when it is detected that the inductor current reaches a current peak value) to detect the freewheel time Tdis of the current inductor, and adjusts the zero-cross reference value ZRef according to the detected freewheel time Tdis.

According to the analysis, the higher the output voltage Vout is, the shorter the freewheeling time Tdis of the inductor is, the larger the resonance amplitude of the inductor current is, the larger the change amplitude of the signal Vts to be detected for representing the inductor current when the zero-crossing occurs is, so that the change of the signal Vts to be detected is easier to detect, and at this time, the zero-crossing reference value ZRef can be appropriately set to a larger value to improve the anti-interference capability; when the output voltage Vout is lower, the corresponding freewheel time Tdis is longer, the resonance amplitude of the inductor current is smaller, and the variation amplitude of the signal to be detected Vts when the zero-crossing occurs is smaller, so that the variation of the signal to be detected is not easy to detect, and at this time, the zero-crossing reference value ZRef can be appropriately set to a smaller value to improve the sensitivity.

The zero-cross detection circuit 1210 provided in the embodiment of the present invention can detect the duration of the freewheeling state of the inductor to obtain the freewheeling time Tdis, and continuously decrease the zero-cross reference value ZRef (in a continuous adjustment manner as shown in fig. 5, a linear adjustment manner may be used) or in a stepwise manner (or in a stepwise manner) (in a stepwise adjustment manner as shown in fig. 5 or in another non-linear adjustment manner), or in a linear-non-linear mixed adjustment manner, along with the gradual increase of the detected freewheeling time Tdis, so as to continuously improve the sensitivity of the zero-cross detection circuit 1210 to the change of the signal to be detected, so that the zero-cross of the inductor current can be more easily detected by the zero-cross detection circuit 1210.

In some embodiments of the step-wise adjustment of the zero-crossing reference value ZRef, referring to the curve corresponding to the step-wise adjustment manner in fig. 5, the interval of the freewheel time Tdis corresponding to the same one of the zero-crossing reference values ZRef may be a fixed time interval. However, the embodiments of the present invention are not limited thereto, in other embodiments that adjust the zero-cross reference value ZRef in a segmented manner, an interval of the freewheel time Tdis corresponding to one zero-cross reference value ZRef may be set according to a peak current of the inductor current, where a duration of the interval is, for example, positively correlated with the peak current, that is, the larger the peak current is, the wider a range of the freewheel time Tdis corresponding to the corresponding one zero-cross reference value ZRef is; in further embodiments, the interval of the freewheel time Tdis corresponding to a zero-crossing reference value ZRef may be set in dependence on the amplitude of the output voltage, the duration of the interval being for example negatively correlated with the amplitude of the output voltage, i.e. the higher the output voltage, the smaller the range of the freewheel time Tdis corresponding to a respective one of the zero-crossing reference values ZRef.

It should be noted that the embodiment of the present invention is not limited to directly comparing the signal representing the zero-crossing reference value ZRef with the signal to be detected, and the zero-crossing reference value may be a value equivalent to the synergistic effect of a plurality of signals.

2.3 switch drive Circuit

The switch driving circuit 1230 is connected to the current detecting circuit 1220 and the zero crossing detecting circuit 1210, respectively, and is configured to generate a switch control signal GT according to the peak indication signal Vpkd and the zero crossing indication signal Vzcd, where the switch control signal GT controls the turn-off of the power driving transistor M1 in response to the peak indication signal Vpkd provided by the current detecting circuit 1220, and controls the turn-on of the power driving transistor M1 in response to the zero crossing indication signal Vzcd provided by the zero crossing detecting circuit 1210. As an alternative embodiment, the level-change edge (rising edge or falling edge) of the peak indicator signal Vpkd is used to determine the falling edge of the switch control signal GT, and the level-change edge of the zero-crossing indicator signal Vzcd is used to determine the rising edge of the switch control signal GT, so that the power driver M1 can be turned on and off at the right moment under the control of the switch control signal GT.

As an alternative embodiment, as shown in fig. 3, the switch driving circuit 1230 may include a logic control unit 1231 and a driving output unit 1232. The logic control unit 1231 is configured to generate a logic control signal Vgt _ pre according to the logic levels of the peak indicator signal Vpkd and the zero-crossing indicator signal Vzcd, and the driving output unit 1232 is configured to drive the logic control signal Vgt _ pre to provide the corresponding switch control signal GT to the control terminal of the power driving transistor M1.

As a non-limiting example, the logic control unit 1231 may be implemented by an RS flip-flop. Wherein, the set input terminal of the RS flip-flop may be connected to the zero-crossing detection circuit 1210 to receive the zero-crossing indication signal Vzcd, the reset input terminal of the RS flip-flop may be connected to the current detection circuit 1220 to receive the peak indication signal Vpkd, and the RS flip-flop provides the corresponding logic control signal Vgt _ pre according to the peak indication signal Vpkd and the zero-crossing indication signal Vzcd.

As a non-limiting example, the driving output unit 1232 may include at least one buffer cascaded, an input terminal of the first-stage buffer receiving the logic control signal Vgt _ pre provided by the logic control unit 1231, and an output terminal of the last-stage buffer providing the corresponding switch control signal GT.

2.4 overvoltage detection circuit

As shown in fig. 3, to implement the functions of overvoltage detection and overvoltage protection, the controller 1200 may further include an overvoltage detection circuit 1240.

The overvoltage detection circuit 1240 may determine whether the output voltage provided by the switching power supply circuit 1000 exceeds a desired value according to the freewheeling time Tdis of the inductor current provided by the zero-cross detection circuit 1210 and a preset overvoltage reference value, and provide an overvoltage indication signal Vovd according to the determination result, which may be used to control the switch driving circuit 1230 (e.g., the control logic control unit 1231) to adjust the duty ratio of the switch control signal GT and/or control the zero-cross detection circuit 1210 to cause the zero-cross detection circuit to adjust the zero-cross reference value ZRef according to the overvoltage indication signal Vovd.

As can be seen from the above analysis, since the amplitude of the output voltage Vout is in a negative correlation, even in a proportional relationship, with the freewheeling time Tdis of the inductor current, in some embodiments, the overvoltage detection circuit 1240 may compare the freewheeling time Tdis provided by the zero-cross detection circuit 1210 with the overvoltage reference value, and when the freewheeling time Tdis exceeds the maximum freewheeling time Tdis _ max represented by the overvoltage reference value, it indicates that the switching power supply circuit 1000 has an overvoltage phenomenon, i.e., the output voltage Vout exceeds the expected value.

Further, in some embodiments, when the over-voltage indication signal indicates that no over-voltage phenomenon has occurred, i.e., when the output voltage is less than the desired value, the zero-crossing detection circuit 1210 may set the zero-crossing reference value ZRef to a first preset value (an initial default value of the zero-crossing reference value) under the control of the over-voltage indication signal; when the overvoltage indicating signal represents that an overvoltage phenomenon occurs, namely when the output voltage is greater than or equal to the expected value, the zero-crossing detection circuit can set the zero-crossing reference value ZRef to be a second preset value under the control of the overvoltage indicating signal, and the second preset value is smaller than the first preset value, so that the switching of the two zero-crossing reference values is realized, and the sectional adjustment of the zero-crossing reference value ZRef is simply realized.

The operation of the switching power supply circuit of the present embodiment will be described below with reference to fig. 4.

The first stage is as follows: when the switch control signal GT is in an active level state (in this embodiment, the switch control signal GT is in a logic high level state in the active level state), the power driving transistor M1 is turned on, a current path from the positive input end of the input voltage to the ground is formed by the load, the inductor L1, the power driving transistor M1, and the sampling resistor Rcs, the inductor current flowing through the inductor L1 continuously increases, the inductor L1 stores energy, and the sampling resistor Rcs provides a sampling voltage CS representing the inductor current.

And a second stage: when the sampling voltage CS at the two ends of the sampling resistor Rcs reaches the voltage value corresponding to the set peak value of the inductor current, the switch control signal GT output by the controller 1200 is changed from the active level state to the inactive level state (in this embodiment, the switch control signal GT is at a logic low level in the inactive level state), so that the power driving tube M1 is turned off, the inductor current flowing through the inductor L1 continues current through the diode D1, the zero-crossing detection circuit 1210 starts timing to detect the inductor current-continuing time Tdis, at this time, the inductor L1, the diode D1 and the output capacitor Cout form a current-continuing circuit, the inductor L1 releases energy to the output capacitor Cout, and the inductor current flowing through the inductor L1 gradually decreases; as the detected freewheel time Tdis continuously increases, the zero-crossing detection circuit 1210 adjusts the zero-crossing reference value ZRef to adjust the sensitivity of the zero-crossing detection.

And a third stage: when the inductor current flowing through the inductor L1 is reduced to zero, the second end (drain) of the power driving transistor M1 generates resonance, and therefore, the zero-crossing detection circuit 1210 can determine whether the inductor current flowing through the inductor L1 reaches 0 by detecting the signal Vts to be detected (e.g., the drain voltage of the power driving transistor M1); when or after the zero-crossing detection circuit 1210 detects that the inductor current reaches 0 (critical conduction mode), the driving circuit 1230 may output the switch control signal GT in an active level state to turn on the power driving transistor M1.

The switching power supply circuit operates cyclically in the order of the first to third stages described above, thereby being able to adaptively maintain the output voltage Vout at a constant voltage value.

Fig. 6a shows a schematic circuit diagram of one implementation of a zero crossing detection circuit of an embodiment of the present invention. Fig. 6b shows a schematic circuit diagram of another implementation of a zero crossing detection circuit of an embodiment of the invention.

As shown in fig. 6a and 6b, the zero crossing detecting circuit of the embodiment of the present invention may include a detecting unit, which may include a converting module 1211, a reference voltage generating module 1212, and a comparator 1213, and an adjustment signal generating unit 1214. In some embodiments (as shown in fig. 6 b), the zero crossing detection circuit 1210 may further include a delay unit 1215 for filtering narrow pulses.

The reference voltage generation module 1212 is configured to generate a first reference voltage Vref 1.

The conversion module 1211 is coupled to a current output terminal (shown in fig. 1 and fig. 2) of the inductor L1 to obtain a signal to be detected Vts (e.g., a drain voltage VD of the power driving transistor M1 or a signal GT provided by a gate), and converts the signal to be detected into a resonant sampling voltage Vtr according to a conversion coefficient k, where k is a positive number.

In the following, the embodiments of the present invention will be described based on Vtr ═ k × Vts, however, the embodiments of the present invention are not limited thereto, and the resonant sampling voltage Vtr may be positively correlated with the ratio Vts/k between the signal to be detected and the conversion coefficient.

The adjustment signal generation unit 1214 is configured to start timing from an initial value when the power driving transistor M1 is turned off to detect the freewheeling time Tdis of the inductor L1 and generate an adjustment signal (e.g., the adjustment signals ST1 to ST3 shown in fig. 6a and 6 b) according to the detected freewheeling time Tdis, where the adjustment signal is applied to the reference voltage generation module 1212 to adjust the first reference voltage Vref1 and/or applied to the conversion module 1211 to adjust the conversion coefficient k, thereby implementing adjustment of the zero-crossing reference value ZRef.

For example, the adjustment signal generating unit 1214 may provide an adjustment signal ST2 according to the freewheel time Tdis, the reference voltage generating module 1212 being controlled by the adjustment signal ST2 to provide a variable first reference voltage Vref1, wherein the first reference voltage Vref1 continuously decreases or stepwise decreases with increasing freewheel time Tdis.

As an alternative embodiment, the adjustment signal generating unit 1214 may include: a first current source for providing a first charging current and a first capacitor. The first terminal of the first capacitor starts receiving the first charging current when the power driving transistor M1 is turned off to provide a timing voltage for characterizing the freewheel time Tdis, and is reset to an initial potential characterizing an initial value when the zero-crossing indication signal Vzcd characterizes that the inductor current has dropped to zero. In the adjusting signal generating unit 1214, a timing control signal may be generated according to the drain voltage VD of the power driving transistor or other signals that can indicate whether the inductor is in the freewheeling stage, and the charging and resetting of the first capacitor may be controlled according to the timing control signal. The adjustment signal generation unit 1214 may adjust the zero-cross reference value Vref according to the timing voltage or a digital signal corresponding to the timing voltage.

The comparator 1213 is configured to provide a zero crossing indication signal Vzcd according to a comparison result of the resonant sampling voltage Vtr and the first reference voltage Vref 1.

As an example, as shown in fig. 6a, the non-inverting input of the comparator 1213 receives the first reference voltage Vref1, the inverting input receives the resonant sampling voltage Vtr, and the output directly provides the zero crossing indication signal Vzcd.

As another embodiment, as shown in fig. 6b, the non-inverting input of the comparator 1213 receives the first reference voltage Vref1, the inverting input receives the resonant sampling voltage Vtr, and the output provides the zero crossing indication signal Vzcd via the delay unit 1215. The delay unit 1215 is configured to filter out narrow pulses (pulse width less than a preset pulse width) in the zero crossing indication signal Vzcd to avoid erroneously indicating a zero crossing.

The adjustment signal generating unit 1214 may further provide an adjustment signal ST3 according to the freewheel time Tdis, and the adjustment signal ST3 acts on the delay unit 1215 to adjust the preset pulse width, which is, for example, negatively correlated with the freewheel time Tdis, i.e., the shorter the freewheel time Tdis is, the longer the zero-crossing detection circuit needs to improve the anti-interference capability against the glitch and the like, so the longer the preset pulse width may be.

The zero-cross reference value ZRef in the present embodiment is defined exemplarily below. From the above analysis, the condition that the zero-crossing detection circuit 1210 outputs the valid zero-crossing indication signal Vzcd is:

Vts<ZRef (1)

in the zero-crossing detection circuit according to the embodiment of the present invention, the condition that the comparator 1213 outputs the effective zero-crossing indication signal Vzcd is as follows:

Vtr<Vref1 (2)

according to the function of the conversion module 1211 in this embodiment, it is known that:

Vtr＝Vts*k (3)

substituting equation (3) into inequality (2) yields:

as can be seen from the inequalities (1) and (4), in the present embodiment, the zero-crossing reference value ZRef used for determining whether to cross zero is Vref1/k, that is, the zero-crossing reference value ZRef is a design parameter defined by the first reference voltage Vref1 and the conversion coefficient k, and when adjusting the zero-crossing reference value ZRef, only the first reference voltage Vref1 and/or the conversion coefficient k need to be adjusted, and the zero-crossing reference value ZRef is not generated by using a circuit structure.

As shown in fig. 9, the delay unit 1215 may include: current source CS2, capacitor C10, reset switch M10, comparator U0 and inverter INV 0. The current source CS2 is used to provide a constant or charging current Ics2 that varies according to a preset trend; the capacitor C10 is connected in series between the current output end of the second current source CS2 and the reference ground; a reset switch M10 is connected in parallel with the capacitor C10, and the control end of the reset switch is connected with the output end of the comparator U0; the positive phase input end of the comparator U0 receives a second reference voltage Vref2 representing a preset pulse width, the negative phase input end is connected with the non-grounding end of the capacitor C10, and the output end provides a zero-crossing indication signal Vzcd.

The output of comparator 1213 outputs a zero crossing indication signal Vzcd via delay unit 1215. An input end of the inverter INV0 is connected to the output end of the comparator 1213, and an output end of the inverter INV0 is connected to the control end of the reset switch M10.

The following description will be given by taking the reset switch M10 as an N-channel transistor as an example, however, the embodiment of the present invention is not limited thereto, the reset switch M10 may also be a P-channel transistor, and a person skilled in the art may add the inverter INV0 or omit the inverter INV0 according to different types of transistors, and may also implement the reset switch M10 and its corresponding functions by using other structures having switching functions.

When the first reference voltage Vref1 is less than/equal to the resonant sampling voltage Vtr, the comparator 1213 outputs a low logic level, and the inverter INV0 outputs a high logic level to turn on the reset switch M10, so that the voltage Vc of the non-ground terminal of the capacitor C10 is reset to the ground reference.

When the first reference voltage Vref1 is greater than the resonant sampling voltage Vtr, the comparator 1213 outputs a high logic level, the inverter INV0 outputs a low logic level to turn off the reset switch M10, the current source CS2 starts to charge the capacitor C10, so that the voltage Vc of the non-ground terminal of the capacitor C10 starts to rise from the reference ground, and when the voltage Vc rises to be greater than the second reference voltage Vref2, which indicates that the pulse width output by the comparator 1213 is greater than the preset pulse width represented by the second reference voltage Vref2, the comparator U0 outputs a zero-crossing indication signal Vzcd of the high logic level.

The delay unit 1215 shown in fig. 9 delays the output signal of the comparator 1213 to provide the delayed zero-crossing indication signal Vzcd, thereby filtering out narrow pulses having a pulse width smaller than a preset pulse width from the zero-crossing indication signal Vzcd.

It should be noted that the circuit configuration shown in fig. 9 is only one implementation of the delay unit 1215, and the delay unit may be implemented by other circuit configurations. For example, in some other embodiments, the non-inverting input terminal and the inverting input terminal of the comparator U0 can be interchanged and the corresponding circuit structure can be adjusted accordingly, the inverter INV0 can be omitted or replaced by a buffer, etc.

As an alternative embodiment, the adjustment signal generating unit 1214 may provide the adjustment signal ST3 to the delay unit 1215 according to the freewheel time Tdis, so that at least one of the magnitude of the charging current Ics2, the capacitance value of the capacitor C10, and the second reference voltage Vref2 is changed to adjust the preset pulse width for filtering the narrow pulses. The preset pulse width decreases, for example, with increasing freewheel time Tdis, i.e. the preset pulse width is inversely related to the freewheel time.

As shown in fig. 7a and 7b, the converting module 1211 may be connected to the drain of the power driving transistor M1 (the converting module may also be connected to the drain of the power driving transistor M1 through another resistor or capacitor) to couple to the current output terminal of the inductor L1, and obtain the signal to be detected (the drain voltage VD).

Implementation mode one of the conversion module 1211

In the implementation shown in fig. 7a, the conversion module 1211 may be a filter (e.g., a high-pass filter). The conversion coefficient k of the conversion module 1211 is positively correlated with the RC time constant of the filter. The filter can filter the signal Vts to be detected so as to reduce the resonance amplitude of the signal to be detected; the zero-crossing reference value ZRef may be decreased by increasing the RC time constant while the first reference voltage Vref1 is constant.

As a specific example, as shown in fig. 7a, the conversion module 1211 includes a capacitor Ca and a resistor Ra sequentially connected in series between the drain of the power driving transistor M1 and the ground. The node connecting the capacitor Ca and the resistor Ra provides the resonant sampling voltage Vtr, and since the RC time constant of the filter is equal to the product of the capacitance value of the capacitor Ca and the resistance value of the resistor Ra, the conversion coefficient k is positively correlated with the capacitance value of the capacitor Ca and the resistance value of the resistor Ra.

The adjustment signal generating unit 1214 provides a corresponding adjustment signal ST1 according to the freewheel time Tdis, and the capacitance value of the capacitor Ca and/or the resistance value of the resistor Ra are controlled by the adjustment signal ST1, such that the capacitance value of the capacitor Ca and/or the resistance value of the resistor Ra continuously increases or stepwise increases with the increase of the freewheel time Tdis.

Implementation mode two of the conversion module 1211

In the implementation shown in fig. 7b, the conversion module 1211 may be a voltage division network (e.g., implemented by a plurality of resistors). The conversion coefficient k of the conversion module 1211 is related to the voltage dividing coefficient of the voltage dividing network.

As a specific example, as shown in fig. 7b, the conversion module 1211 includes a resistor Rb1 and a resistor Rb2 connected in series between the drain of the power driving transistor M1 and the ground in sequence, a node where the resistor Rb1 and the resistor Rb2 are connected provides the resonant sampling voltage Vtr, and the conversion coefficient k is inversely related to the ratio of the resistances of the resistor Rb1 and the resistor Rb 2.

The adjustment signal generating unit 1214 provides a corresponding adjustment signal ST1 according to the freewheel time Tdis, and the resistance values of the resistor Rb1 and/or the resistor Rb2 are controlled by the adjustment signal ST1, so that the ratio of the resistance values of the resistor Rb1 and the resistor Rb2 continuously decreases or stepwise decreases with the increase of the freewheel time Tdis.

In other embodiments, as shown in fig. 7c and 7d, the converting module 1211 may be connected to the gate of the power driving transistor M1 (the converting module may also be connected to the gate of the power driving transistor M1 through another resistor or capacitor) to couple to the current output terminal of the inductor L1 and obtain the signal to be detected.

Implementation mode three of conversion module 1211

In the implementation shown in fig. 7c, the conversion module 1211 includes an enable switch Mc1 and a detection resistance unit, and may further include a clamping element Mc 2.

The enable switch Mc1 is turned on alternately with the power driver M1, and the control terminal of the enable switch Mc1 is controlled by, for example, an inverted signal of the switch control signal GT. The enable switch Mc1 may be implemented by a transistor of the field effect transistor or the like type.

The detecting resistor unit and the enabling switch Mc1 are connected in series between the gate of the power driving transistor M1 and the reference ground, and the conversion coefficient k of the conversion module 1211 is related to the total resistance of the detecting resistor unit. When the enable switch Mc1 is turned on, under the coupling effect (for example, caused by the gate-drain parasitic capacitance of the power driving transistor M1) generated between the gate of the power driving transistor M1 and the current output terminal of the inductor L1, the gate of the power driving transistor M1 provides the signal to be detected, so that the gate voltage of the power driving transistor M1 can be detected as the resonant sampling voltage Vtr.

The clamping element Mc2 is connected in parallel with the detection resistance unit. When the switching control signal GT turns off the power driving transistor M1, the clamping element Mc2 limits the gate voltage (i.e., the resonant sampling voltage Vtr) of the power driving transistor M1 so that the gate voltage does not exceed the set threshold and the power driving transistor M1 cannot be turned on by mistake. The clamping element Mc2 may be implemented by a PNP transistor or an NPN transistor, for example, when a PNP transistor is used as the clamping element Mc2, an emitter is connected to the first end of the sensing resistor unit, and a base and a collector are connected to the second end of the sensing resistor unit. In some embodiments, a first terminal of the detection resistance unit may be coupled to the gate of the power driving transistor M1 via the enable switch Mc1, and a second terminal of the detection resistance unit is connected to the ground reference; in other embodiments, the first terminal of the sensing resistor unit may be directly coupled to the gate of the power driving transistor M1, and the second terminal of the sensing resistor unit is connected to the ground reference via the enable switch Mc 1.

The adjustment signal generating unit 1214 provides a corresponding adjustment signal ST1 according to the freewheel time Tdis, and the total resistance value of the sensing resistor unit is controlled by the adjustment signal ST1, so that the total resistance value of the sensing resistor unit continuously increases or increases stepwise with the increase of the freewheel time Tdis.

As an alternative embodiment, as shown in fig. 7c, the detection resistance unit may include a plurality of first detection resistances Rc _1 to Rc _ n, and may further include a plurality of first detection switches Sc _1 to Sc _ n, where n is a natural number greater than 1. In an alternative embodiment, the number of the first detection switches may be different from the number of the first detection resistors.

The first end of each first detection resistor is respectively connected with the reference ground through a corresponding first detection switch, the second ends of the first detection resistors are mutually connected, and the enabling switch Mc1 is connected between the first end of each first detection resistor and the reference ground in series or between a common connection point of the second ends of the first detection resistors and the control end of the power driving tube M1 in series.

The adjustment signal generating unit 1214 provides signals for controlling the plurality of first detection switches, the signals including a plurality of adjustment signals ST1 (which may also be referred to as a plurality of sub-signals, which may be a plurality of analog signals or multi-bit data of digital signals), and the plurality of adjustment signals ST1 respectively control the turn-on and turn-off of the corresponding first detection switches to adjust the total resistance value of the detection resistance unit.

As a preferred embodiment, at the initial turn-on time of the enable switch Mc1, each first detection switch is turned on under the control of a corresponding regulation signal ST1, and each first detection switch is sequentially turned off by a corresponding one of the regulation signals ST1 as the freewheel time Tdis increases, so that the total resistance value of the detection resistance unit can be increased stepwise as the freewheel time Tdis increases.

As another alternative embodiment, as shown in fig. 7d, the detection resistance unit may include a plurality of second detection resistances Rd _1 to Rd _ m, and may further include a plurality of second detection switches Sd _1 to Sd _ m, where m is a natural number greater than 1. In an alternative embodiment, the number of the second detection switches may be different from the number of the first detection resistors.

The plurality of second detection resistors Rd _1 to Rd _ M are sequentially connected in series between the control end of the power driving transistor M1 and the reference ground, the connection node between every two adjacent second detection resistors is respectively connected with the reference ground through a corresponding second detection switch, and the enable switch Mc1 is connected in series between the first second detection resistor Rd _1 and the control end of the power driving transistor M1 or between the last second detection resistor Rd _ n and the reference ground.

The adjustment signal generating unit 1214 provides a plurality of adjustment signals ST1 (which may be a plurality of analog signals, or multi-bit data of digital signals), and the plurality of adjustment signals ST1 respectively control the on and off of the corresponding second detection switches to adjust the total resistance of the detection resistor units.

As a preferred embodiment, as shown in fig. 8, at the time of turning on of the enable switch Mc1, the plurality of second detection switches are sequentially turned on and off under the control of the respective adjustment signals ST1[1: m ] as the freewheel time Tdis increases, so that the total resistance value of the detection resistance unit can be increased stepwise as the freewheel time Tdis increases.

The embodiment of the invention also provides the zero-crossing detection circuit and the zero-crossing detection method.

In accordance with the present invention, as set forth above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The scope of the invention should be determined from the following claims.

Claims

1. A zero-crossing detection circuit for providing a zero-crossing indication signal based on a signal to be detected, the signal to be detected being responsive to an inductor current provided by an inductor, the inductor being charged when a power switching tube is on and discharged to enable freewheeling when the power switching tube is off, the power switching tube being configured to convert an input voltage to an output voltage, the zero-crossing detection circuit comprising:

the detection unit is used for judging whether the inductive current is reduced to zero or not according to the zero-crossing reference value and the signal to be detected and providing the zero-crossing indication signal representing the judgment result; and

and the adjusting signal generating unit is used for detecting the follow current time of the inductor and adjusting the zero-crossing reference value according to the follow current time.

2. A zero-crossing detection circuit as claimed in claim 1,

the output voltage is higher when the freewheel time detected by the adjustment signal generation unit is shorter, the adjustment signal generation unit adjusts the zero-cross reference value so that the sensitivity of the zero-cross detection circuit is adjusted to be low,

when the freewheel time detected by the adjustment signal generation unit is long, the output voltage is low, and the adjustment signal generation unit adjusts the zero-cross reference value so that the sensitivity of the zero-cross detection circuit is increased.

3. A zero-crossing detection circuit as claimed in claim 1, wherein the adjustment signal generation unit adjusts the zero-crossing reference value down continuously or stepwise as the freewheel time increases.

4. A zero-crossing detection circuit according to claim 1, wherein the adjustment signal generation unit decreases the zero-crossing reference value stepwise as the freewheel time increases,

when the free-wheeling time at different moments is in the same one of a plurality of preset time intervals, the corresponding zero-crossing reference values are the same,

the length of each time interval is a fixed value, or the peak current of the inductive current corresponding to the time interval is positively correlated, or the amplitude of the output voltage corresponding to the time interval is negatively correlated.

5. A zero-crossing detection circuit as claimed in claim 1, wherein the adjustment signal generation unit starts timing from an initial value to obtain a timing signal when the power switching tube is turned off, and adjusts the zero-crossing reference value according to the timing signal,

wherein the adjustment signal generation unit stops timing when the zero-crossing indication signal indicates that the inductor current has dropped to zero, and the timing signal indicates a freewheeling time that the inductor has elapsed since the power switching tube was turned off.

6. A zero-crossing detection circuit as claimed in claim 5, wherein the adjustment signal generation unit adjusts the zero-crossing reference value in accordance with a comparison of the timing signal and at least one reference time value such that the zero-crossing reference value decreases stepwise with an increase in the freewheel time.

7. A zero-crossing detection circuit as claimed in claim 1, wherein the detection unit comprises:

the conversion module is used for converting the signal to be detected into resonance sampling voltage according to a conversion coefficient;

the reference voltage generating module is used for generating a first reference voltage; and

a comparison module providing the zero crossing indication signal according to a comparison result of the resonant sampled voltage and the first reference voltage,

wherein the zero-crossing reference value is positively correlated with the first reference voltage and negatively correlated with the conversion coefficient.

8. A zero-crossing detection circuit as claimed in claim 7, wherein the adjustment signal generation unit comprises:

a first current source providing a charging current;

a first capacitor having a first terminal that begins to receive the charging current when the power drive transistor is turned off to provide a clocking voltage indicative of the freewheel time and is reset to an initial potential indicative of the initial value when the zero-crossing indication signal indicates that the inductor current has dropped to zero,

the adjusting unit adjusts the first reference voltage and/or the conversion coefficient according to the timing voltage or a digital signal corresponding to the timing voltage so as to adjust the zero-crossing reference value.

9. A zero-crossing detection circuit as claimed in claim 7, wherein the converting module is coupled to the second end of the power driving transistor to couple to the current output terminal of the inductor and obtain the signal to be detected.

10. A zero-crossing detection circuit as claimed in claim 9, wherein the conversion module comprises a second capacitor and a first resistor connected in series between the second terminal of the power driving transistor and a reference ground, a node connecting the second capacitor and the first resistor provides the resonant sampled voltage, and the conversion coefficient is positively related to a product of a capacitance value of the second capacitor and a resistance value of the first resistor.

11. A zero-crossing detection circuit as claimed in claim 10, wherein the adjustment signal generation unit provides a corresponding first adjustment signal in dependence on the freewheel time,

and the capacitance value of the second capacitor and/or the resistance value of the first resistor continuously increase or increase in a stepped manner along with the increase of the free-wheeling time under the control of the first adjusting signal.

12. A zero-crossing detection circuit as claimed in claim 9, wherein the conversion module comprises a second resistor and a third resistor connected in series between the second end of the power driving transistor and the reference ground, the node where the second resistor and the third resistor are connected provides the resonant sampled voltage, and the conversion coefficient is negatively related to the ratio of the resistance values of the second resistor and the third resistor.

13. A zero-crossing detection circuit as claimed in claim 12, wherein the adjustment signal generating unit provides a corresponding second adjustment signal according to the freewheel time, the resistance value of the second resistor and/or the third resistor is controlled by the second adjustment signal,

under the action of the second adjusting signal, the ratio of the resistance values of the second resistor and the third resistor is continuously reduced or is reduced in a step mode along with the increase of the free-wheeling time.

14. A zero-crossing detection circuit as claimed in claim 7, wherein the adjustment signal generating unit provides a corresponding third adjustment signal according to the freewheel time, the reference voltage generating module is controlled by the third adjustment signal to provide the variable first reference voltage,

wherein the first reference voltage decreases continuously or in steps with an increase in the freewheel time.

15. A zero-crossing detection circuit as claimed in claim 7, wherein the conversion module is connected to the control terminal of the power driving transistor to couple with the current output terminal of the inductor and obtain the signal to be detected.

16. A zero-crossing detection circuit as claimed in claim 15, wherein the conversion module comprises:

the enabling switch is alternatively conducted with the power driving tube;

a sensing resistance unit connected in series with the enable switch between a control terminal of the power driving transistor and a reference ground, the conversion coefficient being positively correlated with a resistance value of the sensing resistance unit,

when the enable switch is turned on, the control end of the power driving tube provides the resonance sampling voltage according to the signal to be detected under the coupling action of the control end of the power driving tube and the current output end of the inductor.

17. A zero-crossing detection circuit as claimed in claim 16, wherein the conversion module further comprises a clamping element in parallel with the detection resistance unit,

when the power driving tube is turned off, the clamping element clamps the resonance sampling voltage, so that the resonance sampling voltage does not exceed a set threshold value and the power driving tube cannot be turned on.

18. A zero-crossing detection circuit as claimed in claim 16, wherein the adjustment signal generating unit provides a corresponding fourth adjustment signal according to the freewheel time, the resistance value of the detection resistor unit is controlled by the fourth adjustment signal,

wherein the total resistance value of the detection resistance unit is continuously increased or is increased in a stepwise manner along with the increase of the free-wheeling time.

19. A zero-crossing detection circuit as claimed in claim 18, wherein the detection resistance unit includes a plurality of first detection resistances and a plurality of first detection switches,

the first end of each first detection resistor is respectively connected with the reference ground through a corresponding first detection switch, the second ends of the plurality of first detection resistors are interconnected, the enabling switch is connected between the first end of each first detection resistor and the reference ground in series or between a common connection point of the second ends of the plurality of first detection resistors and the control end of the power driving tube in series,

and the multiple sub-signals of the fourth adjusting signal respectively control the on and off of each first detection switch so as to adjust the total resistance value of the detection resistance unit.

20. A zero-crossing detection circuit as claimed in claim 19, wherein the plurality of first detection switches are all turned on under the control of the fourth adjustment signal at the initial turn-on time of the enable switch, and are sequentially turned off by respective sub-signals of the fourth adjustment signal as the freewheel time increases.

21. A zero-crossing detection circuit as claimed in claim 18, wherein the detection resistors comprise a plurality of second detection resistors and a plurality of second detection switches,

the second detection resistors are sequentially connected in series between the control end of the power driving tube and a reference ground, a connection node between every two second detection resistors is respectively connected with the reference ground through a corresponding second detection switch, the enabling switch is connected in series between the second detection resistors and the control end of the power driving tube or between the second detection resistors and the reference ground,

and the plurality of sub-signals of the fourth adjusting signal respectively control the on and off of each second detection switch so as to adjust the resistance value of the detection resistor.

22. A zero-crossing detection circuit as claimed in claim 21,

and at the initial conduction moment of the enabling switch, the plurality of second detection switches are all conducted under the control of the fourth adjusting signal, and the plurality of second detection switches are sequentially turned off by corresponding sub-signals of the fourth adjusting signal along with the increase of the free-wheeling time.

23. A zero-crossing detection circuit as claimed in claim 6, wherein the comparison module comprises:

and a positive phase input end of the first comparator receives the first reference voltage, a negative phase input end of the first comparator receives the resonance sampling voltage, and an output end of the first comparator provides the zero-crossing indication signal.

24. A zero-crossing detection circuit as claimed in claim 23, further comprising a delay unit connected to the output of the first comparator for filtering out narrow pulses of the zero-crossing indication signal having a pulse width less than a preset pulse width.

25. A zero-crossing detection circuit as claimed in claim 24, wherein the adjustment unit provides a fifth adjustment signal to the delay unit in dependence on the freewheel time to adjust the preset pulse width such that the preset pulse width is inversely related to the freewheel time.

26. A switching power supply circuit, comprising:

a zero-crossing detection circuit as claimed in any one of claims 1 to 25;

a load capacitor providing the output voltage;

the control end of the power driving tube is controlled by a switch control signal;

the inductor is used for providing an inductor current, and the inductor current flows to the current output end of the inductor through the current input end of the inductor;

and the driving circuit provides the switch control signal according to the zero-crossing indication signal.

27. The switching power supply circuit according to claim 26, further comprising an auxiliary driving transistor connected in series between the current output terminal of the inductor and the second terminal of the power driving transistor, wherein a control terminal of the auxiliary driving transistor receives a conduction level for conducting the auxiliary driving transistor.

28. The switching power supply circuit according to claim 26, further comprising:

the sampling resistor is connected between the first end of the power driving tube and the reference ground in series; and

a current detection circuit coupled to the first end of the power driving tube to obtain a current sampling voltage, and determining whether the inductor current has reached the current peak value according to the current sampling voltage, and providing a peak value indication signal representing the determination result,

wherein the drive circuit provides the switch control signal in accordance with the zero crossing indication signal and the peak indication signal.

29. The switching power supply circuit according to claim 26, further comprising an overvoltage detection circuit for judging whether said output voltage exceeds a desired value based on said freewheel time and an overvoltage reference value and providing an overvoltage indication signal based on the judgment result,

the over-voltage indication signal controls the driving circuit to adjust a duty cycle of the switch control signal and/or controls the zero-crossing detection circuit to cause the zero-crossing detection circuit to adjust the zero-crossing reference value according to the over-voltage indication signal.

30. The switching power supply circuit according to claim 29,

when the over-voltage indication signal indicates that the output voltage is less than the desired value, the zero-crossing reference value is equal to a first preset value,

when the over-voltage indication signal indicates that the output voltage is greater than/equal to the desired value, the zero-crossing reference value is equal to a second preset value,

the first preset value is greater than the second preset value.

31. A zero-crossing detection method for providing a zero-crossing indication signal according to a signal to be detected, the signal to be detected being responsive to an inductor current provided by an inductor, the inductor being charged when a power switching tube is turned on and discharged to realize a follow current when the power switching tube is turned off, the power switching tube being configured to convert an input voltage to an output voltage, the zero-crossing detection method comprising:

judging whether the inductive current is reduced to zero or not according to a zero-crossing reference value and the signal to be detected, and providing a zero-crossing indication signal representing a judgment result;

detecting a freewheel time of the inductor; and

adjusting the zero-crossing reference value according to the freewheel time.

32. A zero-crossing detection method as claimed in claim 31,

when the detected freewheel time is short, the output voltage is high, the zero-crossing reference value is adjusted such that the sensitivity of zero-crossing detection is adjusted low,

when the detected freewheel time is longer, the output voltage is lower, and the zero-crossing reference value is adjusted such that the sensitivity of zero-crossing detection is adjusted higher.

33. A zero-crossing detection method as claimed in claim 31, wherein the step of adjusting the zero-crossing reference value comprises:

the zero-crossing reference value is adjusted continuously low or stepwise as the freewheel time increases.

34. A zero-crossing detection method as claimed in claim 30, characterized in that the zero-crossing reference value is stepped down as the freewheel time increases,

the length of each time interval is a fixed value, or the peak current of the inductive current corresponding to the time interval is positively correlated, or the amplitude of the output voltage corresponding to the time interval is negatively correlated, and the output voltage is provided by the power switch tube and the switching power supply circuit where the inductor is located.

35. A zero-crossing detection method as claimed in claim 31, wherein the step of detecting the freewheel time comprises:

starting timing from an initial value to obtain a timing signal when the power switch tube is turned off, wherein the timing signal represents the freewheeling time of the inductor from the time when the power switch tube is turned off; and

and stopping timing when the zero-crossing indication signal indicates that the inductive current has dropped to zero.

36. A zero-crossing detection method as claimed in claim 35, wherein the step of adjusting the zero-crossing reference value comprises:

adjusting the zero-crossing reference value in dependence on a comparison of the timing signal and at least one reference time value such that the zero-crossing reference value decreases stepwise with increasing freewheel time.

37. A zero-crossing detection method as claimed in claim 31, wherein the step of providing the zero-crossing indication signal comprises:

converting the signal to be detected into resonance sampling voltage according to a conversion coefficient; and

providing the zero crossing indication signal based on a comparison of the resonant sampled voltage and a first reference voltage,

38. A zero-crossing detection method as claimed in claim 37, wherein the conversion factor increases continuously or in a stepwise manner with an increase in the freewheel time.

39. A zero-crossing detection method as claimed in claim 37, wherein the first reference voltage is continuously or stepwise decreased as the freewheel time increases.

40. A zero-crossing detection method as claimed in claim 37, wherein the step of adjusting the zero-crossing reference value comprises:

when the power driving tube is turned off, starting to charge a first capacitor by using a charging current, so that a first end of the first capacitor provides a timing voltage for representing the freewheeling time;

when the zero-crossing indication signal indicates that the inductor current has dropped to zero, the first terminal of the first capacitor is reset to an initial potential that indicates the initial value; and

and adjusting the first reference voltage and/or the conversion coefficient according to the timing voltage or a digital signal corresponding to the timing voltage so as to adjust the zero-crossing reference value.

41. A zero-crossing detection method as claimed in claim 37, wherein the second terminal of the power driving transistor is coupled to the current output terminal of the inductor to provide the signal to be detected.

42. A zero-crossing detection method as claimed in claim 41, wherein the conversion coefficient is positively correlated to a time constant of a filter, an input terminal of the filter is coupled to the second terminal of the power driving tube, and an output terminal of the filter provides the resonant sampling voltage.

43. A zero-crossing detection method as claimed in claim 41, wherein the conversion factor is a voltage dividing factor of a voltage dividing resistor network, an input terminal of the voltage dividing resistor network is coupled to the second terminal of the power driving transistor, and an output terminal of the voltage dividing resistor network provides the resonant sampling voltage.

44. A zero-crossing detection method as claimed in claim 37, wherein a control terminal of the power driving transistor is coupled to a current output terminal of the inductor to provide the signal to be detected.

45. A zero-crossing detection method as claimed in claim 45, wherein the conversion coefficient is a total resistance of a detection resistance unit, the detection resistance unit is coupled between the current output terminal and a reference ground, and provides the resonance sampling voltage related to the total resistance under the action of the signal to be detected.

46. A zero-crossing detection method as claimed in claim 31, wherein the step of providing the zero-crossing indication signal comprises:

and delaying the zero-crossing indicating signal to filter out narrow pulses with pulse widths smaller than a preset pulse width in the zero-crossing indicating signal.

47. A zero-crossing detection method as claimed in claim 46, wherein the step of providing the zero-crossing indication signal further comprises:

and adjusting the preset pulse width according to the follow current time, so that the preset pulse width is inversely related to the follow current time.