CN115995979A - Quick-response flyback converter and control method thereof - Google Patents
Quick-response flyback converter and control method thereof Download PDFInfo
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Abstract
The invention provides a flyback converter with quick response and a control method thereof, wherein the flyback converter comprises the following components: transformer, main switching tube and control circuit, this control circuit includes: the feedback unit is used for generating a compensation signal according to an output feedback signal of the flyback converter; the first control unit is used for controlling the switching frequency of the flyback converter to enter a frequency conversion stage along with the output feedback signal or the change of the compensation signal, and adjusting the frequency change slope of the flyback converter in the frequency conversion stage according to the first sampling signal. The frequency change slope of the flyback converter in the frequency conversion stage is adjusted according to the output voltage, so that the frequency change slope is slower in low-voltage output, loop control is stable, output power can be continuously adjusted, dynamic response is fast, and the system can achieve both fast dynamic response and loop stability in the full output voltage range.
Description
Technical Field
The invention relates to the technical field of switching power supplies, in particular to a flyback converter with quick response and a control method thereof.
Background
The flyback converter has the advantages of simple circuit structure and low cost, and is widely applied to low-power supplies and various power adapters. The conventional flyback converter currently comprises a conventional flyback converter (shown in fig. 1 a), an active clamp flyback converter (shown in fig. 1 b) and an asymmetric half-bridge flyback converter (shown in fig. 1 c), wherein a primary side switching tube Q1 is a main switching tube, a switching tube Q2 is an auxiliary switching tube, and a secondary side diode D1 is a rectifying tube in fig. 1b and 1 c. Each flyback converter mainly stores energy in a primary side energy storage element of the converter during the conduction period of the main switching tube Q1, and the energy stored in the primary side energy storage element is transferred to a secondary side part after the switching tube Q1 is turned off.
The closed-loop control scheme of the existing flyback converter mainly sets corresponding thresholds f and vcs_ref for controlling the on and off of the main switching tube Q1 according to the compensation signal Vcomp, as shown in fig. 2, the frequency-limiting threshold (which can be used herein to characterize the switching frequency of the flyback converter) and the current threshold vcs_ref are both curves related to the compensation signal Vcomp, wherein the frequency-limiting threshold f has a minimum frequency-limiting value and a maximum frequency-limiting value, and thus the switching frequency of the flyback converter includes the minimum switching frequency f min Stage, highest switching frequency f max Stage and at the lowest switching frequency f min And a highest switching frequency f max Frequency conversion stage between. To meet the high frequency requirement, the slope of the curve of the frequency limiting threshold f and Vcomp is steeper during the frequency conversion phase. Based on the closed-loop control scheme, the switching frequency is lower at low-voltage output, and the highest switching frequency f of the flyback converter is higher for the direct-current working point of a low frequency band under the same disturbance max The larger the frequency variation amplitude is, the larger the maximum switching frequency f is max The system loop response is too fast, and the system stability is poor, corresponding to the V1-V2 stage in fig. 2.
To ensure system stability over the full output voltage range, it is necessary to slow down the loop response, but this can affect the dynamic performance of the system. For example, when the flyback converter operates in QR mode, the low-voltage output down-converter will enter quasi-resonant state earlier, corresponding to the change of the compensation signal Vcomp, but the power P is unchanged, the equivalent gain is 0, the response is too slow, and the output ripple of the converter will be increased, corresponding to the V2-V3 stage in fig. 2. Thus, existing control schemes have difficulty guaranteeing both system dynamic and steady state performance from the peripheral loop. In fig. 2, a solid line corresponds to an expected setting case at full-range output, a broken line a corresponds to a case at actual low-voltage output, and a broken line b corresponds to a case at actual high-voltage output.
Accordingly, there is a need to provide an improved solution to overcome the above technical problems in the prior art.
Disclosure of Invention
In order to solve the technical problems, the invention provides a flyback converter with quick response and a control method thereof, wherein the frequency change slope of the flyback converter in a frequency conversion stage is adjusted according to output voltage, so that the frequency change slope is slower during low-voltage output, loop control is stable, output power can be continuously adjusted, dynamic response is quick, and a system can realize both quick dynamic response and loop stability in a full output voltage range.
According to a first aspect of the present invention there is provided a fast response flyback converter comprising: the transformer, main switch tube and with the control circuit that main switch tube is connected, wherein, control circuit includes:
the feedback unit is used for generating a compensation signal according to an output feedback signal of the flyback converter;
the first control unit is used for controlling the switching frequency of the flyback converter to enter a frequency conversion stage along with the change of the output feedback signal or the compensation signal, and adjusting the frequency change slope of the flyback converter in the frequency conversion stage according to the first sampling signal.
Optionally, the first control unit obtains a conducting signal for controlling the main switching tube to be conducted according to the first sampling signal and the compensating signal, so as to adjust the frequency change slope of the flyback converter in the frequency conversion stage.
Optionally, the switching frequency of the flyback converter includes a lowest switching frequency and a highest switching frequency, and the frequency conversion stage is a stage between the lowest switching frequency and the highest switching frequency.
Optionally, the frequency change slope of the flyback converter in the frequency conversion stage is positively correlated with the output voltage of the flyback converter.
Optionally, the first control unit includes:
a timing threshold adjustment unit configured to adjust a timing threshold according to a superimposed signal of the compensation signal and the first sampling signal, a magnitude of the timing threshold being inversely related to a magnitude of the superimposed signal;
a timing unit configured to start timing when a turn-on signal of the main switching tube is detected;
and the first comparison unit is configured to trigger to generate a conduction signal of the main switching tube in the next switching cycle when the timing value of the timing unit reaches the timing threshold value.
Optionally, the first control unit includes:
a charging unit configured to charge a preset first capacitor with a first charging current in each switching cycle of the flyback converter;
the voltage resetting unit is configured to reset the voltage of the first capacitor according to the conduction signal of the main switching tube;
a first comparison unit configured to trigger generation of a turn-on signal of the main switching tube when a voltage across the first capacitor rises to a first voltage threshold,
wherein the first charging current is obtained based on a superimposed signal of the compensation signal and the first sampling signal, and the first voltage threshold is a preset fixed value.
Optionally, the first control unit includes:
a charging control unit configured to obtain a first charging current according to the compensation signal, and charge a first capacitor with the first charging current;
a first processing circuit configured to perform subtraction processing on the first sampling signal and a first voltage threshold signal to obtain a second voltage threshold,
and the second comparison unit is configured to trigger to generate a conduction signal of the main switching tube when the voltage of two ends of the first capacitor rises to the second voltage threshold value and trigger to reset the voltage of the first capacitor.
Optionally, the transformer comprises an auxiliary winding, the first sampled signal being obtained based on a sample-and-hold of the auxiliary winding signal.
Optionally, the first control unit is further configured to generate a current threshold from the compensation signal and to obtain the turn-off signal of the main switching tube when a second sampling signal characterizing the excitation current of the flyback converter reaches the current threshold.
Optionally, during the frequency conversion phase, the current threshold is constant.
According to a second aspect of the present invention, there is provided a control method of a fast-response flyback converter, the flyback converter comprising a transformer and a main switching tube, the control method comprising:
generating a compensation signal according to an output feedback signal of the flyback converter;
and after the flyback converter follows the output feedback signal or the compensation signal to enter a frequency conversion stage, adjusting the frequency change slope of the flyback converter in the frequency conversion stage according to a first sampling signal representing the output voltage of the flyback converter.
Optionally, adjusting the frequency change slope of the flyback converter in the frequency conversion stage according to the first sampling signal includes: and obtaining a conduction signal for controlling the conduction of the main switching tube according to the first sampling signal and the compensation signal, so as to adjust the frequency change slope of the flyback converter in the frequency conversion stage.
Optionally, the frequency change slope of the flyback converter in the frequency conversion stage is positively correlated with the output voltage of the flyback converter.
Optionally, the switching frequency of the flyback converter includes a lowest switching frequency and a highest switching frequency, and the frequency conversion stage is a stage between the lowest switching frequency and the highest switching frequency.
Optionally, the transformer comprises an auxiliary winding, the first sampled signal being obtained based on a sample-and-hold of the auxiliary winding signal.
The beneficial effects of the invention at least comprise:
according to the embodiment of the invention, the frequency change slope of the flyback converter in the frequency conversion stage is adjusted according to the sampling signal representing the output voltage, so that the frequency change slope is slower during low-voltage output, a loop is easier to stabilize, the output power can be continuously adjusted, the output ripple is reduced, and the system can realize both fast dynamic response and loop stability in the full output voltage range.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
Drawings
FIG. 1a is a schematic diagram of a circuit configuration of a conventional QR flyback converter;
FIG. 1b shows a schematic circuit diagram of an active clamp flyback converter;
FIG. 1c is a schematic diagram showing a circuit configuration of an asymmetric half-bridge flyback converter according to the prior art;
FIG. 2 is a graph showing the relationship between the control threshold and the power of the flyback converter according to the compensation signal;
fig. 3 is a schematic circuit diagram of a fast-response flyback converter according to an embodiment of the present invention;
fig. 4a shows a schematic structural diagram of a first control unit provided according to a first embodiment of the present invention;
fig. 4b shows a schematic structural diagram of a first control unit provided according to a second embodiment of the present invention;
fig. 4c shows a schematic structural diagram of a first control unit provided according to a third embodiment of the present invention;
FIG. 5 is a graph showing the control threshold and power as a function of compensation signal according to an embodiment of the present invention;
fig. 6 shows a flow chart of a control method of a fast response flyback converter according to an embodiment of the present invention.
Detailed Description
In order that the invention may be readily understood, a more complete description of the invention will be rendered by reference to the appended drawings. Preferred embodiments of the present invention are shown in the drawings. The invention may, however, be embodied in different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
In the present invention, the technical solution of the present invention will be exemplified by only a QR flyback converter. It should be appreciated that the disclosed solution is also applicable to other types of flyback converters such as active clamp flyback converters, asymmetric half-bridge flyback converters AHB, etc.
As shown in fig. 3, in an embodiment of the present invention, a fast response flyback converter (also referred to herein as a flyback converter) includes: a transformer TR including a primary winding Np, a secondary winding Ns, and an auxiliary winding Na, a main switching tube Q1, and a control circuit 100. The excitation inductance and leakage inductance of the primary winding Np are equivalent to inductances Lm and Lk, respectively.
One end of the primary winding Np is connected with an input end of the input voltage Vin, the other end of the primary winding Np is connected with a drain electrode of the main switching tube Q1, and a source electrode of the main switching tube Q1 is connected with a reference ground through a sampling resistor Rcs. The gate of the main switching tube Q1 is connected to the control circuit 100, and the capacitor C1 is a parasitic capacitance of the main switching tube Q1. The main switching tube Q1 transfers energy from the primary side portion of the flyback converter to the secondary side portion through periodic switching. In some possible embodiments, the main switching transistor Q1 is an NMOS field effect transistor or GAN device.
The secondary side portion of the transducer includes: a rectifying tube (e.g. diode or field effect transistor) D1 and an output capacitance Co. Taking diode D1 as an example, its anode is connected to the secondary winding Ns and its cathode is connected to the output of the flyback converter. The positive pole of output capacitor Co is connected with the output of flyback converter, and output capacitor Co's negative pole is connected with reference ground, and the homonymous end of secondary winding Ns is also connected with reference ground simultaneously. Further, the output end of the flyback converter is connected with a load, and the load receives the electric energy (such as voltage and current) converted by the flyback converter. In some examples, the power converted by the flyback converter is also passed through a filter before reaching the load. In some examples, the filter is a subcomponent of the flyback converter, an external component of the flyback converter, and/or a subcomponent of the load. In any case, the load may perform a function using filtered or unfiltered electrical energy from the flyback converter. Alternatively, the load may include, but is not limited to, a computing device and related components or any other type of electrical device and/or circuitry that receives voltage or current from the flyback converter.
The control circuit 100 includes: a feedback unit 110, a first control unit 120, and a driver 130.
The feedback unit 110 is configured to generate the compensation signal Vcomp according to an output feedback signal (such as a feedback signal of the output voltage Vo or a feedback signal of the output current Io) of the flyback converter. The feedback unit 110 specifically includes a voltage feedback loop for obtaining the compensation signal Vcomp from sampling the output voltage Vo, and a current feedback loop. The circuit structure of the feedback unit 110 may be an existing conventional circuit structure, for example, the compensation signal Vcomp is obtained by resistive sampling and comparing by a comparator, and capacitance compensation, which is specifically understood with reference to the prior art, and the present invention is not limited thereto.
The first control unit 120 receives a first sampling signal Vs representing the output voltage Vo of the flyback converter, is used for controlling the switching frequency f of the flyback converter to enter the frequency conversion stage following the output feedback signal of the flyback converter or the change of the compensation signal Vcomp, and adjusts the frequency change slope of the flyback converter in the frequency conversion stage according to the first sampling signal Vs.
In this embodiment, the first control unit 120 is specifically configured to obtain a conducting signal for controlling the main switching tube Q1 to be conducted according to the first sampling signal Vs and the compensation signal Vcomp, so as to adjust the frequency change slope of the flyback converter in the frequency conversion stage according to the output voltage Vo of the flyback converter. The on signal of the main switching transistor Q1 may be, for example, a control signal Vgs1 in a high-level state.
Referring to fig. 5, a relationship curve between a switching frequency f of the flyback converter and a compensation signal Vcomp is shown as fig. 5, where when a voltage value of the compensation signal Vcomp is smaller than a preset value V1, the switching frequency f of the flyback converter is set to be unchanged at a corresponding minimum switching frequency (denoted as fmin), and in this stage, the system mainly adjusts an off time of the main switching tube Q1 by adjusting a current threshold vcs_ref, that is, adjusts an on time of the main switching tube Q1 to change a duty ratio under the condition that the voltage value of the compensation signal Vcomp is unchanged, so as to adjust the output voltage Vo. When the voltage value of the compensation signal Vcomp is greater than the preset value V1 and less than the preset value V3, the set current threshold vcs_ref remains unchanged, and in this stage, the system mainly adjusts the on time of the main switching tube Q1 by adjusting the switching frequency f of the flyback converter between the lowest switching frequency fmin and the highest switching frequency, so as to realize the adjustment of the output power, which is the frequency conversion stage of the flyback converter. The case when the voltage value of the compensation signal Vcomp is greater than the preset value V3 is similar to the case when it is smaller than V1, except that: when the voltage value of the compensation signal Vcomp is greater than the preset value V3, the switching frequency f of the flyback converter is set to be unchanged at the corresponding highest switching frequency (denoted fmax).
In the frequency conversion stage, the first control unit 120 controls the change slope of the switching frequency f of the flyback converter (i.e., the frequency change slope) to be positively correlated with the output voltage Vo of the flyback converter. That is, the first control unit 120 controls the change slope of the switching frequency f of the flyback converter to increase with an increase of the output voltage Vo of the flyback converter and to decrease with a decrease of the output voltage Vo of the flyback converter, as shown in fig. 5, when the output voltage Vo of the flyback converter has the highest valueAt the maximum value Vomax, the first control unit 120 controls the frequency change slope of the flyback converter to be the maximum, and at this time, the highest switching frequency value f of the flyback converter max_Vomax Maximum; when the output voltage Vo of the flyback converter has the minimum value Vomin, the first control unit 120 controls the frequency variation slope of the flyback converter to be minimum, and the highest switching frequency value f of the flyback converter is the same max_Vomin Minimum. The first control unit 120 reduces the frequency change slope of the flyback converter when low-voltage input is performed, so that the feedback loop of the system is easier to stabilize, and in the process, the current threshold vcs_ref is basically kept unchanged or the change amplitude is small, so that the output power can be continuously adjusted, thereby reducing the output ripple and being beneficial to the normal performance of the power transmission of the system.
The circuit structure and principle of the first control unit 120 in the different embodiments of the present invention will be described with reference to fig. 4a to 4c and fig. 5:
example 1
In this embodiment, as shown in fig. 4a, the first control unit 120 includes: timing threshold adjustment unit 121, timing unit 122, comparison unit 123, off control unit 124, and RS flip-flop 125. Wherein the timing threshold adjusting unit 121 is configured to adjust the timing threshold Tr in accordance with the superimposed signal vcomp+vs of the compensation signal Vcomp and the first sampling signal Vs, and the magnitude of the timing threshold Tr is inversely related to the magnitude of the superimposed signal vcomp+vs. The timer unit 122 is configured to start timing when detecting that the on signal of the main switching tube Q1 is valid in the last switching period, i.e., the main switching tube Q1 is turned on. The comparing unit 123 is configured to output a turn-on trigger signal to the set terminal of the RS flip-flop 125 when the timing value T1 of the timing unit 122 reaches the timing threshold Tr, thereby triggering the RS flip-flop 125 to output the control signal Vgs1 of the high level to turn on the main switching tube Q1, and simultaneously triggering the timing unit 122 to restart timing. The first sampled signal Vs is a signal sampled and obtained by the sample-and-hold module 200 based on the signal of the auxiliary winding Na, and can be used to characterize the output voltage Vo information of the flyback converter.
The off control unit 124 is configured to respond to the compensation signalVcomp generates a current threshold Vcs_ref and obtains the turn-off signal of the main switching transistor Q1 when the second sampling signal Vcs reaches the current threshold Vcs_ref. Wherein the turn-off signal of the main switch Q1 may be, for example, a control signal Vgs1 in a low-level state, and the second sampling signal Vcs is a signal obtained by sampling based on the sampling resistor Rcs, and may be used to characterize the exciting current of the flyback converter (denoted as i Lm ) Information. Specifically, the circuit structure and the working principle of the turn-off control unit 124 can be understood with reference to the prior art, and the detailed description thereof is omitted herein since it does not affect the solution of the technical problem of the present invention.
Referring to fig. 5, in the stage where the compensation signal Vcomp is smaller than V1, the timing threshold adjusting unit 121 constantly outputs a larger timing threshold Tr, so that the switching frequency f of the flyback converter is constantly maintained at the lowest switching frequency, and meanwhile, the current threshold vcs_ref increases with the increase of the compensation signal Vcomp in this stage, that is, the frequency requirement of the flyback converter in the working mode when the output power P is not high is satisfied, and the requirement of adjusting the output voltage Vo of the flyback converter is also satisfied.
In the frequency conversion stage, the timing threshold outputted by the timing threshold adjusting unit 121 decreases as the superimposed signal vcomp+vs increases. The first sampling signal Vs increases with an increase in the output voltage Vo, and the superimposed signal vcomp+vs increases by a larger amount with an increase in the first sampling signal Vs, so that the timing threshold Tr output by the timing threshold adjusting unit 121 decreases by a larger amount with an increase in the output voltage Vo, the manifestation in the switching frequency is: the slope of the change in the switching frequency f increases with an increase in the output voltage Vo, and decreases with a decrease in the output voltage Vo. Therefore, when the flyback converter outputs low voltage, the frequency change slope of the flyback converter is slower, so that the feedback loop of the system is easier to stabilize, and the normal transmission of the power P of the system is facilitated. At the same time, the current threshold vcs_ref remains substantially constant during this phase as the compensation signal Vcomp increases.
In the phase where the compensation signal Vcomp is greater than V3, the timing threshold adjustment unit 121 constantly outputs a smaller timing threshold Tr so that the switching frequency f of the flyback converter is constantly maintained at the highest switching frequency, and the higher the output voltage Vo, the higher the highest switching frequency of the switching frequency f of the flyback converter. At the same time, the current threshold vcs_ref continues to increase with an increase in the compensation signal Vcomp during this phase.
Based on the above description, the present embodiment can realize normal transmission of the system power P in the full output voltage range.
Example two
In this embodiment, as shown in fig. 4b, the first control unit 120 includes: a charging unit 126, a voltage resetting unit 127, a comparing unit 128, an RS flip-flop 125, and a turn-off control unit 124.
Wherein the charging unit 126 is configured to charge the preset first capacitor Cf with the first charging current in each switching cycle of the flyback converter. Illustratively, the charging unit 126 includes, for example, a voltage-controlled current source I5. The voltage-controlled current source I5 is connected in series with the first capacitor Cf, and the voltage-controlled current source I5 is controlled by the superimposed signal vcomp+vs of the compensation signal Vcomp and the first sampling signal Vs to provide the first charging current.
The voltage reset unit 127 is configured to voltage reset the first capacitor Cf according to the on signal of the main switching transistor Q1. Illustratively, the voltage reset unit 127, for example, a switch K3, the switch K3 being connected in parallel with the first capacitor Cf, and the switch K3 being configured to be controlled to be turned on when the on signal of the main switching tube Q1 is active or to be controlled to be turned on according to the on trigger signal of the main switching tube Q1, thereby providing a voltage reset path for the first capacitor Cf.
The comparison unit 128 is configured to output a turn-on trigger signal to the set terminal of the RS flip-flop 125 when the voltage Vcf across the first capacitor Cf rises to the first voltage threshold, thereby triggering the RS flip-flop 125 to output the control signal Vgs1 of high level to turn on the main switching transistor Q1 while triggering the voltage reset unit 127 to perform voltage reset on the first capacitor Cf. The first voltage threshold is a preset fixed value Vref1.
In this embodiment, the duration of one switching cycle of the flyback converter corresponds to the sum of the charging duration when the voltages at the two ends of the first capacitor Cf are charged from the initial potential point to the first voltage threshold Vref1 and the duration when the voltages at the two ends of the first capacitor Cf are reset from the first voltage threshold Vref1 to the initial potential point.
It should be noted that, in this embodiment, only the circuit structure portion for providing the charging current and the voltage reset to the first capacitor Cf in the frequency conversion stage is shown, and the circuit structure portion for providing the constant charging current to the first capacitor Cf in the constant frequency stage does not affect the solution of the technical problem of the present invention, so it is not described herein, and can be understood with reference to the prior art.
The structure and function of the off control unit 124 can be understood with reference to the first embodiment, and will not be described herein.
Referring to fig. 5, in the stage where the compensation signal Vcomp is smaller than V1, the charging current of the first capacitor Cf is constant, so that the switching frequency f of the flyback converter is kept constant at the lowest switching frequency, and meanwhile, the current threshold vcs_ref increases with the increase of the compensation signal Vcomp in this stage, which not only meets the frequency requirement of the flyback converter in the working mode when the output power P is not high, but also meets the regulation requirement of the output voltage Vo of the flyback converter.
In the frequency conversion stage, the first charging current increases with an increase in the superimposed signal vcomp+vs. The first sampling signal Vs increases with an increase in the output voltage Vo, and the superimposed signal vcomp+vs increases by a larger amount with an increase in the first sampling signal Vs, so that the first charging current increases by a larger amount with an increase in the output voltage Vo, which is manifested in a switching frequency: the slope of the change in the switching frequency f increases with an increase in the output voltage Vo, and decreases with a decrease in the output voltage Vo. Therefore, when the flyback converter outputs low voltage, the frequency change slope of the flyback converter is slower, so that the feedback loop of the system is easier to stabilize, and the normal transmission of the power P of the system is facilitated. Meanwhile, the current threshold vcs_ref is constant with an increase in the compensation signal Vcomp during this stage.
In the phase when the compensation signal Vcomp is greater than V3, the charging current of the first capacitor Cf is constant, so that the switching frequency f of the flyback converter is kept constant at the highest switching frequency, and the higher the output voltage Vo, the higher the highest switching frequency of the switching frequency f of the flyback converter. At the same time, the current threshold vcs_ref continues to increase with an increase in the compensation signal Vcomp during this phase.
Based on the above description, the present embodiment can realize normal transmission of the system power P in the full output voltage range.
It can be appreciated that the circuit structure of the first control unit 120 in this embodiment is simple.
Example III
In this embodiment, as shown in fig. 4c, the first control unit 120 includes: a charge control unit 129, a voltage reset unit 131, a processing unit 132, a comparison unit 133, an RS flip-flop 125, and a turn-off control unit 124.
The charging control unit 129 is configured to obtain a first charging current according to the compensation signal Vcomp in each switching period of the flyback converter, and charge the preset first capacitor Cf with the first charging current. Illustratively, the charge control unit 129 includes, for example, a voltage controlled current source I6. The voltage-controlled current source I6 is connected in series with the first capacitor Cf, and the voltage-controlled current source I6 is controlled by the compensation signal Vcomp to provide a first charging current.
The voltage reset unit 131 is configured to perform voltage reset on the first capacitor Cf according to the on signal of the main switching transistor Q1. Illustratively, the voltage reset unit 131 is, for example, a switch K3, where the switch K3 is connected in parallel with the first capacitor Cf, and the switch K3 is configured to be controlled to be turned on when the on signal of the main switching tube Q1 is active or to be controlled to be turned on according to the on trigger signal of the main switching tube Q1, thereby providing a voltage reset path for the first capacitor Cf.
The processing unit 132 is configured to perform subtraction processing on the first sampling signal Vs and the first voltage threshold signal to obtain a second voltage threshold. The first voltage threshold signal is a preset fixed value Vref1, the second voltage threshold is a difference signal Vref1-k×vs between the preset fixed value Vref1 and the k-times first sampling signal Vs, and k is a positive number. The processing unit 132 is illustratively a subtractor circuit.
The comparison unit 133 is configured to output a turn-on trigger signal to the set terminal of the RS flip-flop 125 when the voltage Vcf across the first capacitor Cf rises to the second voltage threshold, thereby triggering the RS flip-flop 125 to output the control signal Vgs1 of the high level to turn on the main switching transistor Q1 while triggering the voltage reset unit 127 to perform voltage reset on the first capacitor Cf.
The structure and function of the off control unit 124 can be understood with reference to the first embodiment, and will not be described herein.
Referring to fig. 5, in the frequency conversion stage, the first sampling signal Vs increases with an increase in the output voltage Vo, and the second voltage threshold decreases by a larger amount with an increase in the first sampling signal Vs, so that the second voltage threshold decreases by a larger amount with an increase in the output voltage Vo, which is manifested in a switching frequency: the slope of the change in the switching frequency f increases with an increase in the output voltage Vo, and decreases with a decrease in the output voltage Vo. Therefore, when the flyback converter outputs low voltage, the frequency change slope of the flyback converter is slower, so that the feedback loop of the system is easier to stabilize, and the normal transmission of the system power P is facilitated. Meanwhile, the current threshold vcs_ref is constant with an increase in the compensation signal Vcomp during this stage.
Further, the present invention also provides a control method of a flyback converter with fast response, which can be used in the flyback converters described in the foregoing fig. 3 to 5. As shown in fig. 6, the control method includes performing the steps of:
in step S1, a compensation signal is generated from an output feedback signal of the flyback converter.
In step S2, after the flyback converter follows the output feedback signal or the compensation signal to enter the frequency conversion stage, the frequency change slope of the flyback converter in the frequency conversion stage is adjusted according to the first sampling signal representing the output voltage of the flyback converter.
In this embodiment, adjusting the frequency change slope of the flyback converter in the frequency conversion stage according to the first sampling signal includes: and obtaining a conduction signal for controlling the conduction of the main switching tube according to the first sampling signal and the compensation signal, so as to adjust the frequency change slope of the flyback converter in the frequency conversion stage. The switching frequency of the flyback converter is positively correlated with the output voltage of the flyback converter in the frequency change slope of the frequency conversion stage.
Optionally, in some embodiments of the present invention, obtaining a conduction signal for controlling conduction of the main switching tube according to the first sampling signal and the compensation signal further includes: adjusting a timing threshold according to the superimposed signal of the compensation signal and the first sampling signal, wherein the magnitude of the timing threshold is inversely related to the magnitude of the superimposed signal; starting timing when the on signal of the main switching tube is detected; triggering and generating a conduction signal of the main switching tube in the next switching period when the timing value reaches the timing threshold value. Wherein the first sampled signal is sample-and-hold obtained based on the auxiliary winding.
In other embodiments of the present invention, obtaining a conduction signal for controlling conduction of the main switching tube according to the first sampling signal and the compensation signal further includes: charging a preset first capacitor by using a first charging current in each switching period of the flyback converter; triggering to generate a conduction signal of the main switching tube when the voltage at two ends of the first capacitor rises to a first voltage threshold value; and voltage resetting is carried out on the first capacitor according to the conduction signal of the main switching tube. The first charging current is obtained based on a superposition signal of the compensation signal and the first sampling signal, and the first voltage threshold is a preset fixed value.
In still other embodiments of the present invention, obtaining a conduction signal for controlling conduction of the main switching tube according to the first sampling signal and the compensation signal further includes: charging a preset first capacitor by using a first charging current in each switching period of the flyback converter; subtracting the first sampling signal and the first voltage threshold signal to obtain a second voltage threshold; triggering to generate a conduction signal of the main switching tube when the voltage at two ends of the first capacitor rises to a second voltage threshold value; and voltage resetting is carried out on the first capacitor according to the conduction signal of the main switching tube. The first charging current is obtained based on the compensation signal, and the first voltage threshold is a preset fixed value.
It should be noted that, the specific implementation of each step in the control method of the flyback converter described above may refer to the foregoing embodiment of the flyback converter, which is not described herein again.
In summary, the embodiment of the invention adjusts the frequency change slope of the flyback converter in the frequency conversion stage according to the sampling signal of the output voltage, so that the frequency change slope is slower during low-voltage output, the loop is easier and more stable, the output power can be continuously adjusted, the dynamic response is fast, and the system can realize both dynamic performance and steady-state performance in the whole output voltage range.
It should be noted that, all types of thresholds described herein represent ideal values, and in practical applications, other values within the allowable error range corresponding to the ideal values may also be sampled. Meanwhile, the term "constant" as used herein is to be understood to include both the case of maintaining the value unchanged and the case of slightly fluctuating around the value, within the allowable range of the error of the value.
Finally, it should be noted that: it is apparent that the above examples are only illustrative of the present invention and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. And obvious variations or modifications thereof are contemplated as falling within the scope of the present invention.
Claims (15)
1. A fast response flyback converter comprising: the transformer, main switch tube and with the control circuit that main switch tube is connected, wherein, control circuit includes:
the feedback unit is used for generating a compensation signal according to an output feedback signal of the flyback converter;
the first control unit is used for controlling the switching frequency of the flyback converter to enter a frequency conversion stage along with the change of the output feedback signal or the compensation signal, and adjusting the frequency change slope of the flyback converter in the frequency conversion stage according to the first sampling signal.
2. The flyback converter according to claim 1, wherein the first control unit obtains a conduction signal for controlling the conduction of the main switching tube according to the first sampling signal and the compensation signal, so as to adjust the frequency change slope of the flyback converter in a frequency conversion stage.
3. The flyback converter of claim 1, wherein the switching frequency of the flyback converter comprises a lowest switching frequency and a highest switching frequency, the conversion stage being a stage between the lowest switching frequency and the highest switching frequency.
4. The flyback converter of claim 1, wherein a frequency change slope of the flyback converter during a frequency conversion phase is positively correlated with an output voltage of the flyback converter.
5. The flyback converter of claim 2, wherein the first control unit comprises:
a timing threshold adjustment unit configured to adjust a timing threshold according to a superimposed signal of the compensation signal and the first sampling signal, a magnitude of the timing threshold being inversely related to a magnitude of the superimposed signal;
a timing unit configured to start timing when a turn-on signal of the main switching tube is detected;
and the first comparison unit is configured to trigger to generate a conduction signal of the main switching tube in the next switching cycle when the timing value of the timing unit reaches the timing threshold value.
6. The flyback converter of claim 2, wherein the first control unit comprises:
a charging unit configured to charge a preset first capacitor with a first charging current in each switching cycle of the flyback converter;
the voltage resetting unit is configured to reset the voltage of the first capacitor according to the conduction signal of the main switching tube;
a first comparison unit configured to trigger generation of a turn-on signal of the main switching tube when a voltage across the first capacitor rises to a first voltage threshold,
wherein the first charging current is obtained based on a superimposed signal of the compensation signal and the first sampling signal, and the first voltage threshold is a preset fixed value.
7. The flyback converter of claim 2, wherein the first control unit comprises:
a charging control unit configured to obtain a first charging current according to the compensation signal, and charge a first capacitor with the first charging current;
a first processing circuit configured to perform subtraction processing on the first sampling signal and a first voltage threshold signal to obtain a second voltage threshold,
and the second comparison unit is configured to trigger to generate a conduction signal of the main switching tube when the voltage of two ends of the first capacitor rises to the second voltage threshold value and trigger to reset the voltage of the first capacitor.
8. The flyback converter of claim 1, wherein the transformer comprises an auxiliary winding, the first sampled signal being obtained based on a sample-and-hold of the auxiliary winding signal.
9. The flyback converter of claim 1, wherein the first control unit is further configured to generate a current threshold from the compensation signal and to obtain the turn-off signal of the main switching tube when a second sampling signal representative of the excitation current of the flyback converter reaches the current threshold.
10. The flyback converter of claim 7, wherein the current threshold is constant during the frequency conversion phase.
11. A control method of a fast response flyback converter, the flyback converter comprising a transformer and a main switching tube, wherein the control method comprises:
generating a compensation signal according to an output feedback signal of the flyback converter;
and after the flyback converter follows the output feedback signal or the compensation signal to enter a frequency conversion stage, adjusting the frequency change slope of the flyback converter in the frequency conversion stage according to a first sampling signal representing the output voltage of the flyback converter.
12. The control method of claim 11, wherein adjusting the frequency change slope of the flyback converter at the variable frequency stage according to the first sampling signal comprises: and obtaining a conduction signal for controlling the conduction of the main switching tube according to the first sampling signal and the compensation signal, so as to adjust the frequency change slope of the flyback converter in the frequency conversion stage.
13. The control method of claim 12, wherein a frequency change slope of the flyback converter during a frequency conversion phase is positively correlated with an output voltage of the flyback converter.
14. The control method of claim 11, wherein the switching frequencies of the flyback converter include a lowest switching frequency and a highest switching frequency, and the conversion stage is a stage between the lowest switching frequency and the highest switching frequency.
15. The control method according to any one of claims 11-14, wherein the transformer comprises an auxiliary winding, the first sampled signal being obtained based on a sample-and-hold of the auxiliary winding signal.
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| CN202211527610.8A CN115995979A (en) | 2022-11-30 | 2022-11-30 | Quick-response flyback converter and control method thereof |
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| CN202211527610.8A CN115995979A (en) | 2022-11-30 | 2022-11-30 | Quick-response flyback converter and control method thereof |
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| CN115995979A true CN115995979A (en) | 2023-04-21 |
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