CN113315378B - Control method, control circuit, flyback converter and electronic equipment - Google Patents

Control method, control circuit, flyback converter and electronic equipment Download PDF

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Publication number
CN113315378B
CN113315378B CN202110443827.XA CN202110443827A CN113315378B CN 113315378 B CN113315378 B CN 113315378B CN 202110443827 A CN202110443827 A CN 202110443827A CN 113315378 B CN113315378 B CN 113315378B
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voltage
flyback converter
circuit
primary side
control method
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CN113315378A (en
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罗九兵
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Shanghai Hanmai Electronic Technology Co ltd
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Shanghai Hanmai Electronic Technology Co ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/083—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the ignition at the zero crossing of the voltage or the current
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention provides a control method, a control circuit, a flyback converter and an electronic device. The control method is applied to a secondary side control circuit of a flyback converter and comprises the following steps: obtaining the current of a secondary rectifier tube of the flyback converter, and controlling the secondary rectifier tube to be disconnected when the current of the secondary rectifier tube is equal to a threshold current; wherein the threshold current is a negative value. Compared with the prior art, the control method has smaller switching loss.

Description

Control method, control circuit, flyback converter and electronic device
Technical Field
The invention belongs to the field of control and regulation of converters, relates to a control method, and particularly relates to a control method, a control circuit, a flyback converter and an electronic device.
Background
Flyback converters, also known as single-ended Flyback or Buck-Boost converters, are known for their output to gain energy when the primary winding is disconnected from the power supply. The flyback converter is widely applied to a low-power supply and various power adapters due to the advantages of simple circuit structure, low cost and the like.
Referring to fig. 1A, a typical flyback converter topology is shown. In order to improve the conversion efficiency of the flyback converter, the flyback converter is usually controlled by a quasi-resonance control method in the conventional manner, specifically, referring to fig. 1B, a parasitic capacitor of the primary side MOS transistor M1 and a primary coil of the transformer form an LC oscillating circuit; after the freewheeling of the secondary rectifier M2 is completed (i.e. I)M20, corresponding to time t1 in fig. 1B) turns off M2, at which time the drain voltage V of M1drainWill oscillate with time, and turning on the primary side MOS transistor M1 when the voltage oscillates to the lowest point (corresponding to time t2 in fig. 1B) can reduce the switching loss. Theoretically, the lowest point has a voltage value of Vbulk-Nps×VoutWherein Nps is the primary and secondary turns ratio of the transformer. However, in practical applications, the inventor finds that high switching loss still exists in the manner that the secondary rectifier M2 is turned off after the freewheeling of the secondary rectifier M2 is completed.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, an object of the present invention is to provide a control method, a control circuit, a flyback converter, and an electronic device, which are used to solve the problem of high switching loss in the prior art.
In order to achieve the above and other related objects, a first aspect of the present invention provides a control method, a control circuit, a flyback converter, and an electronic device, which are applied to a secondary side control circuit of the flyback converter, where the control method includes: obtaining the current of a secondary rectifier tube of the flyback converter, and controlling the secondary rectifier tube to be disconnected when the current of the secondary rectifier tube is equal to a threshold current; wherein the threshold current is a negative value.
In an embodiment of the first aspect, the control method further includes: and if the primary circuit of the flyback converter works in a non-zero voltage switching-on state in the current period, adjusting the threshold current to the current negative direction.
In an embodiment of the first aspect, the control method further includes: and if the primary circuit of the flyback converter works in a zero voltage switching-on state in the current period and works in a non-zero voltage switching-on state in the previous period, adjusting the threshold current to the positive current direction.
In an embodiment of the first aspect, the control method further includes: and acquiring the drain voltage of the secondary rectifier tube of the flyback converter, and judging whether the primary circuit of the flyback converter works in a zero-voltage switching-on state or not according to the drain voltage of the secondary rectifier tube of the flyback converter.
A second aspect of the present invention provides another control method, applied to a primary side control circuit of a flyback converter, including: the method comprises the steps of obtaining the drain voltage of a primary side MOS tube of a flyback converter, and controlling the primary side MOS tube to be conducted when the drain voltage of the primary side MOS tube oscillates to a threshold voltage; the threshold voltage is a variable voltage value and is determined by the drain voltage of the primary side MOS tube.
In an embodiment of the second aspect, the control method further includes: if the drain voltage of the primary side MOS tube meets a zero voltage switching-on condition in the current period, setting the threshold voltage of the next period as zero voltage; otherwise, the threshold voltage of the next cycle is set to be the same as the threshold voltage of the current cycle.
In an embodiment of the second aspect, the control method further includes: when the working time of a primary circuit of the flyback converter in a zero-voltage opening state is greater than a time threshold, setting the threshold voltage as an initial threshold voltage, wherein the initial threshold voltage is different from the zero voltage.
A third aspect of the present invention provides a control circuit for controlling a primary side circuit and/or a secondary side circuit of a flyback converter, the control circuit comprising: a primary side control circuit, which controls the primary side circuit of the flyback converter by adopting the control method of any one of the second aspects of the invention; and/or a secondary side control circuit, which controls the secondary side circuit of the flyback converter by adopting the control method of any one of the first aspect of the invention.
A fourth aspect of the present invention provides a flyback converter including: a primary side circuit; a secondary side circuit; a primary side control circuit, which controls the primary side circuit of the flyback converter by adopting the control method of any one of the second aspects of the invention; the secondary side control circuit controls the secondary side circuit of the flyback converter by adopting the control method of any one of the first aspects of the invention.
A fifth aspect of the invention provides an electronic device comprising a flyback converter according to the fourth aspect of the invention.
As described above, the control method, the control circuit, the flyback converter, and the electronic device according to the present invention have the following advantages:
the control method comprises the steps that the secondary rectifying tube is controlled to be disconnected when the current of the secondary rectifying tube is equal to a negative threshold current, and the current flowing through the secondary rectifying tube is a negative current in a time period from the completion of the follow current of the secondary rectifying tube to the disconnection, wherein the negative current can be used as the initial oscillation energy of a transformer to increase the oscillation amplitude of the drain voltage of the primary MOS tube. Therefore, compared with the scheme that the secondary side rectifying tube is disconnected after the follow current is completed, the control method of the invention enables the lowest point of the drain voltage of the primary side MOS tube in the oscillation process to be lower, so that the switching loss is smaller when the primary side MOS tube is conducted at the lowest point.
In addition, the control method can adjust the threshold current according to the drain voltage of the secondary rectifier tube of the flyback converter. As long as the adjustment amount is small enough when the threshold current is adjusted each time, the control method can realize Zero Voltage switching on (ZVS) of the primary side MOS transistor by adjusting the threshold current for multiple times, so as to reduce the switching loss of the primary side MOS transistor as much as possible.
Drawings
Fig. 1A is a diagram illustrating an example of a conventional flyback converter topology.
Fig. 1B is a signal waveform diagram illustrating a flyback converter controlled by a conventional quasi-resonant control method.
Fig. 2A is a flowchart illustrating a control method according to an embodiment of the invention.
Fig. 2B is a signal waveform diagram of the flyback converter controlled by the control method according to the present invention.
Fig. 3A is a waveform diagram of signals when the flyback converter is controlled by the control method according to the present invention.
FIG. 3B is a circuit diagram of a threshold current adjustment circuit employed in an embodiment of the control method of the present invention.
FIG. 4 is a flowchart illustrating a control method according to an embodiment of the present invention.
Fig. 5 is a circuit diagram of a flyback converter according to an embodiment of the invention.
Fig. 6 is a flowchart illustrating a control method of the flyback converter in an embodiment of the invention.
Description of the element reference numerals
M1 primary side MOS tube
M2 secondary side rectifier tube
S11-S12
S41-S42
S61-S67
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict.
It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than being drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of each component in actual implementation may be changed arbitrarily, and the layout of the components may be more complicated. Moreover, in this document, relational terms such as "first," "second," and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.
In order to improve the conversion efficiency of the flyback converter, the conventional method usually adopts a quasi-resonance control method to control the flyback converter, that is: after the freewheeling of the secondary rectifier M2 is completed (i.e. I)M20), M2 is turned off, and the drain voltage V of the primary side MOS transistor M1 is at this timedrainThe primary side MOS transistor M1 is turned on when the voltage oscillates to the lowest point along with the oscillation of the transformer coil, so that the switching loss can be reduced. Theoretically, the voltage value of the lowest point is Vbulk-Nps×VoutWherein Nps is the primary and secondary turns ratio of the transformer. However, in practical applications, the inventor finds that high switching loss still exists in the manner that the secondary rectifier M2 is turned off after the freewheeling of the secondary rectifier M2 is completed. Furthermore, due to the different amplitudes of the global grid voltage, VbulkAlso different. Therefore, for the same flyback converter, the design can ensure that the flyback converter is at low Vbulk(e.g., 90V) has a lower minimum voltage value, howeverWhen V isbulkAt higher voltages (e.g. 380V), the lowest voltage is still high, and there is still a high switching loss.
In view of the above problems, the present invention provides a control method. The control method comprises the steps that the secondary rectifying tube is controlled to be disconnected when the current of the secondary rectifying tube is equal to a negative threshold current, and the current flowing through the secondary rectifying tube is a negative current in a time period from the completion of the follow current of the secondary rectifying tube to the disconnection, wherein the negative current can be used as the initial oscillation energy of a transformer to increase the oscillation amplitude of the drain voltage of the primary MOS tube. Therefore, compared with the scheme that the secondary side rectifying tube is disconnected after the follow current is completed, the control method of the invention enables the lowest point of the drain voltage of the primary side MOS tube in the oscillation process to be lower, so that the switching loss is smaller when the primary side MOS tube is conducted at the lowest point.
In an embodiment of the present invention, the control method is applied to a secondary side control circuit of a flyback converter, where the secondary side control circuit is used to control on and off of a secondary side circuit in the flyback converter. For example, the secondary control circuit may control the secondary circuit by adjusting a gate voltage of the secondary rectifier to turn on and off the secondary rectifier.
Referring to fig. 2A, the control method in the embodiment includes:
and S11, obtaining the current of the secondary rectifier tube of the flyback converter.
And S12, controlling the secondary rectifier tube to be disconnected when the current of the secondary rectifier tube is equal to a threshold current. The threshold current is a negative value, and the value of the threshold current can be set according to an empirical value. The determination of whether the current of the secondary rectifier tube is equal to the threshold current may be performed by a current comparator.
It should be noted that, in this embodiment, a direction from bottom to top of the secondary winding is taken as a positive direction of the current, and the threshold current being a negative value means that the direction of the threshold current is a direction from top to bottom of the secondary winding. In practice, the positive direction may be defined in other ways, and the direction of the threshold current may change accordingly, for example, when the direction of the secondary winding from top to bottom is defined as the positive direction of the current, the threshold current is a positive value.
Specifically, referring to fig. 2B, the freewheeling of the secondary rectifier is completed at time t1, i.e. the current I of the secondary rectifier at time t1M20. Thereafter, keeping the secondary rectifier tube on, thus IM2Will continue to decrease in value. At time t3, IM2Equal to the threshold current, and at the moment, the secondary rectifier tube is controlled to be disconnected.
After the secondary side rectifying tube is disconnected, the drain voltage of the primary side MOS tube generates LC oscillation, and when the drain voltage of the primary side MOS tube oscillates to the lowest point (time t 4), the switching loss can be reduced by controlling the conduction of the primary side MOS tube, and the switching loss is reduced as the lowest point is lower.
For the primary side MOS tube, the oscillation period of the drain voltage of the primary side MOS tube is related to the excitation inductance and the parasitic capacitance of the primary side MOS tube, and the oscillation amplitude of the drain voltage of the primary side MOS tube is related to the energy stored on the transformer at the moment of disconnecting the secondary side rectifier tube: when the secondary rectifier tube is disconnected, the higher the energy stored in the transformer is, the larger the oscillation amplitude of the drain voltage of the primary MOS tube is, and thus the lower the lowest point of the drain voltage of the primary MOS tube is. In this embodiment, since the current value of the secondary rectifier is equal to the threshold current when the secondary rectifier is turned off, a negative current exists in the secondary circuit when the secondary rectifier is turned off, and the negative current serves as the initial oscillation energy of the transformer to increase the oscillation amplitude of the drain voltage of the primary MOS transistor. Compared with the existing scheme, the oscillation amplitude of the original side MOS tube in the embodiment is larger, and the lowest point of the drain voltage is lower, so that the switching loss is smaller.
In this embodiment, the secondary control circuit may control the secondary rectifier tube to be turned on by using the prior art, for example, when the turn-off duration of the secondary rectifier tube reaches a preset value, the secondary rectifier tube is controlled to be turned on, which is not described herein for the sake of brevity.
As mentioned above, controlling the secondary rectifier to be turned off at the threshold current reduces the lowest point of the drain voltage of the primary MOS transistor, so that zero-voltage turn-on of the primary MOS transistor can be achieved by properly setting the threshold current, so as to reduce the switching loss as much as possible. To achieve the object, in an embodiment of the invention, the control method further includes: if the primary circuit of the flyback converter works in a non-zero voltage opening state in the current period, adjusting the threshold current to the current negative direction; and/or if the primary circuit of the flyback converter works in a zero voltage switching-on state in the current period and works in a non-zero voltage switching-on state in the previous period, adjusting the threshold current to the positive current direction. The primary side circuit works in a zero voltage switching-on state, namely that the switching-on voltage of the primary side MOS tube (namely the drain voltage when the primary side MOS tube is switched on) is zero voltage, the primary side circuit works in a non-zero voltage switching-on state, namely that the switching-on voltage of the primary side MOS tube is a value except zero voltage, and the zero voltage means that the voltage value is zero or approximately zero.
Specifically, referring to fig. 3A, the flyback converter is controlled by a quasi-resonant control method in a first period, at this time, the primary side circuit operates in a non-zero voltage on state, and the threshold current is adjusted to a negative direction in the period. Preferably, the adjustment amount of the threshold current is a fixed value at each adjustment. Referring to fig. 3B, a 4-bit 16-step threshold current adjusting circuit is shown, through which the threshold current can be adjusted.
Because the threshold current is adjusted towards the negative direction in the first period, the oscillation amplitude of the drain voltage of the primary side MOS tube is increased in the second period, but the zero voltage switching-on condition is not reached, so that the threshold voltage of the primary side MOS tube is kept unchanged, and at the moment, the primary side circuit works in a non-zero voltage switching-on state. The zero voltage switching-on condition means that the lowest point of the drain voltage of the primary side MOS tube is equal to zero voltage. The primary circuit still works in a non-zero voltage switching-on state in the second period, so that the threshold current is continuously adjusted towards the negative direction in the second period.
Because the threshold current is further adjusted to the negative direction in the second period, the oscillation amplitude of the primary side MOS tube is further increased in the third period, and the drain voltage of the primary side MOS tube reaches a zero-voltage switching-on condition, at the moment, the threshold voltage of the primary side MOS tube in the next period (namely, the fourth period) is set to be zero voltage, and the primary side circuit starts to work in a zero-voltage switching-on state from the fourth period. At this time, the threshold current is still adjusted in the negative direction during the third period.
In the fourth period, the primary side circuit works in a zero-voltage switching-on state, and the previous period (namely, the third period) does not work in the zero-voltage switching-on state, so that the threshold current is adjusted to the positive direction of the current in the fourth period. Preferably, the threshold current is adjusted in the positive direction in the fourth period by the same amount as it is adjusted in the negative direction in the third period.
Optionally, the control method further includes: and if the primary circuit of the flyback converter works in a zero-voltage opening state in the current period and the previous period, keeping the threshold current unchanged. For example, in the fifth period, the primary circuit of the flyback converter operates in the zero-voltage on state in both the current period and the previous period (i.e., the fourth period), and the threshold current is kept unchanged.
Optionally, the control method further includes: after the threshold current is adjusted to the positive direction of the current, the level of a Lock signal is pulled high in the next period, so that the threshold current is not allowed to change any more, and the flyback converter is ensured to continuously work in a zero-voltage switching-on state. For example, the threshold current is adjusted in the positive direction of the current in the fourth period, and the level of the Lock signal is pulled high in the next period (i.e., the fifth period) to keep the threshold current from changing.
In an embodiment of the present invention, the control method further includes: and acquiring the drain voltage of the secondary rectifier tube of the flyback converter, and judging whether the primary circuit of the flyback converter works in a zero-voltage switching-on state or not according to the drain voltage of the secondary rectifier tube of the flyback converter. For example,referring to fig. 1, the voltage across the primary winding of the transformer can be obtained according to the drain voltage of M2 and the turn ratio of the transformer, according to VbulkAnd the voltage across the primary winding of the transformer, the drain voltage of M1 is obtained. Therefore, whether the primary side circuit works in the zero-voltage opening state can be judged according to the drain voltage of M2.
The invention also provides another control method, which is applied to a primary side control circuit of the flyback converter; the secondary side control circuit of the flyback converter adopts the control method shown in fig. 2A to control the secondary side circuit. The primary side control circuit is used for controlling the connection and disconnection of the primary side circuit in the flyback converter. For example, the primary side control circuit can control the on and off of the primary side MOS transistor by adjusting the gate voltage of the primary side MOS transistor, thereby realizing the control of the primary side circuit.
Referring to fig. 4, in an embodiment of the present invention, the control method includes:
and S41, acquiring the drain voltage of the primary side MOS tube of the flyback converter.
And S42, controlling the conduction of the primary side MOS tube when the drain voltage of the primary side MOS tube oscillates to a threshold voltage. The threshold voltage is a variable voltage value and is determined by the drain voltage of the primary side MOS tube.
Optionally, if the drain voltage of the primary side MOS transistor satisfies the zero voltage turn-on condition in the current period, the threshold voltage of the next period is set to be zero voltage; otherwise, the threshold voltage of the next cycle is set to a non-zero voltage, e.g., the threshold voltage of the next cycle may be set to be the same as the threshold voltage of the current cycle.
For example, referring to fig. 3A, in the first period, the drain voltage of the primary side MOS transistor does not satisfy the zero voltage turn-on condition, and the threshold voltage of the next period (i.e., the second period) is set to be the same as the threshold voltage of the current period. In the third period, the drain voltage of the primary side MOS tube meets the zero voltage switching-on condition, and the threshold voltage of the next period (namely, the fourth period) is set to be zero voltage. And starting from the fourth period, the flyback converter works in a zero-voltage opening state.
In order to determine whether the drain voltage of the primary side MOS transistor satisfies a zero voltage turn-on condition, the lowest point of the drain voltage of the primary side MOS transistor in an oscillation period needs to be obtained. In order to achieve the object, in an embodiment of the present invention, a method for controlling conduction of the primary side MOS transistor includes: and in the next oscillation period, when the drain voltage of the primary side MOS tube is equal to the threshold voltage, controlling the conduction of the primary side MOS tube.
In this embodiment, the primary side control circuit may control the conduction of the primary side rectifier tube by using the prior art, for example, control the conduction of the primary side rectifier tube when the turn-off duration of the primary side rectifier tube reaches a preset value, which is not described herein in this specification.
Preferably, to prevent the input and output voltage variation from affecting the zero-voltage turn-on condition, in an embodiment of the present invention, the control method further includes: when the working time of a primary circuit of the flyback converter in a zero-voltage opening state is greater than a time threshold, setting the threshold voltage as an initial threshold voltage, wherein the initial threshold voltage is not zero voltage. And then, the primary side circuit of the flyback converter works in a non-zero voltage switching-on state, the secondary side control circuit continuously adjusts the threshold current, and the primary side control circuit adjusts the threshold voltage until the primary side circuit of the flyback converter works in a zero voltage switching-on state again. Wherein, the time threshold value can be set according to actual requirements.
In this embodiment, the control method enables the primary side control circuit to control the primary side circuit to operate in the non-zero voltage turn-on state at intervals, and enables the primary side circuit to operate in the zero voltage turn-on state again by adjusting the threshold current and the threshold voltage, thereby overcoming the influence of the change of the input voltage and the output voltage on the zero voltage turn-on condition.
Based on the above description of the control method, the present invention further provides a control circuit for controlling the primary side circuit and/or the secondary side circuit of the flyback converter. The control circuit comprises a primary side control circuit and/or a secondary side control circuit, wherein the primary side control circuit controls the primary side circuit of the flyback converter by adopting the control method of the invention, and the secondary side control circuit controls the secondary side circuit of the flyback converter by adopting the control method of the invention.
Based on the description of the control method, the invention also provides a flyback converter. Referring to fig. 5, in an embodiment of the present invention, the flyback converter includes a primary circuit, a secondary circuit, a primary control circuit, and a secondary control circuit. The primary side control circuit is connected with the primary side circuit, and the primary side circuit of the flyback converter is controlled by the control method. The secondary side control circuit is connected with the secondary side circuit, and the control method is adopted to control the secondary side circuit of the flyback converter.
Referring to fig. 6, in an embodiment of the present invention, the specific steps of controlling the flyback converter include:
s61, the primary side control circuit controls the flyback converter to operate in a quasi-resonant second valley voltage conduction state, that is: and when the drain voltage of the primary side MOS tube oscillates to the second valley voltage, controlling the conduction of the primary side circuit.
And S62, the primary side control circuit acquires the drain voltage of the primary side MOS tube and judges whether the drain voltage meets the zero voltage switching-on condition.
And S63, if the drain voltage of the primary side MOS tube does not meet the zero voltage switching-on condition, the primary side control circuit controls the primary side MOS tube to work in a second valley voltage switching-on state in the next period.
S64, if the drain voltage of the primary side MOS transistor satisfies the zero voltage turn-on condition, the primary side control circuit controls the primary side MOS transistor to operate in a first valley bottom voltage conduction state in a next period, that is: and when the drain voltage of the primary side MOS tube oscillates to the first valley voltage, controlling the conduction of the primary side circuit. Wherein the first valley bottom voltage is zero voltage.
And S65, the secondary side control circuit obtains the drain voltage of the secondary side rectifier tube and judges whether the primary side MOS tube works in a first valley bottom voltage conduction state or a second valley bottom voltage conduction state.
And S66, if the primary side MOS tube works in the second valley bottom voltage conducting state, adjusting the threshold current towards the negative current direction, and controlling the secondary side rectifier tube to be disconnected when the current of the secondary side rectifier tube is equal to the threshold current. Thereafter, step S62 is performed in the next cycle.
And S67, if the primary side MOS tube works in the first valley bottom voltage conducting state, adjusting the threshold current to the positive current direction, and controlling the secondary side rectifier tube to be disconnected when the current of the secondary side rectifier tube is equal to the threshold current. Thereafter, the Lock signal is pulled high in the next cycle, thereby no longer allowing the threshold current of the current comparator to change.
Preferably, in order to prevent the input and output voltages from affecting the zero-voltage turn-on condition, the primary side control circuit controls the primary side MOS transistor to operate in the second valley voltage turn-on state at intervals, and re-locks the primary side MOS transistor through the steps S61 to S67.
The invention also provides electronic equipment, and the electronic equipment comprises the flyback converter.
The protection scope of the control method of the present invention is not limited to the execution sequence of the steps illustrated in this embodiment, and all the solutions implemented by the steps addition, subtraction, and step replacement in the prior art according to the principle of the present invention are included in the protection scope of the present invention.
The control method comprises the steps that the secondary rectifying tube is controlled to be disconnected when the current of the secondary rectifying tube is equal to a negative threshold current, and the current flowing through the secondary rectifying tube is a negative current in a time period from the completion of the follow current of the secondary rectifying tube to the disconnection, wherein the negative current can be used as the initial oscillation energy of a transformer to increase the oscillation amplitude of the drain voltage of the primary MOS tube. Therefore, compared with the scheme that the secondary side rectifying tube is disconnected after the follow current is completed, the control method enables the lowest point of the drain voltage of the primary side MOS tube in the oscillation process to be lower, and therefore the switching loss is smaller when the primary side MOS tube is conducted at the lowest point.
In addition, no matter what the voltage value of the Vbulk is, the control method can automatically adjust the threshold current according to the drain voltage of the secondary rectifier tube of the flyback converter, and finally realize zero-voltage switching-on of the primary MOS tube so as to reduce the switching loss of the primary MOS tube as much as possible.
The control method can gradually adjust the threshold current in a plurality of cycles so that the oscillation lowest point of the drain voltage of the primary side MOS tube gradually approaches zero voltage. In addition, the control method informs the secondary side control circuit that the zero-voltage turn-on condition is not detected on the primary side through the two-valley bottom state (or more than two valley bottoms), and informs the secondary side control circuit that the zero-voltage turn-on condition is detected on the primary side through the one-valley bottom state. The zero voltage switching-on conditions of the primary side control circuit and the secondary side control circuit are transmitted through the working mode, and a primary side and a secondary side isolation communication device and a driving circuit are not needed. Moreover, the control method of the present invention can be configured to periodically release the stable condition of the lock and readjust to make the primary side circuit operate again in the zero voltage on state.
In conclusion, the present invention effectively overcomes various disadvantages of the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims (10)

1. A control method is applied to a secondary side control circuit of a flyback converter, and comprises the following steps:
obtaining the current of a secondary rectifier tube of the flyback converter, and controlling the secondary rectifier tube to be continuously conducted when the current of the secondary rectifier tube is equal to 0, until the secondary rectifier tube is controlled to be disconnected when the current of the secondary rectifier tube is equal to a threshold current; wherein the threshold current is a negative value.
2. The control method according to claim 1, characterized by further comprising:
and if the primary circuit of the flyback converter works in a non-zero voltage switching-on state in the current period, adjusting the threshold current to the current negative direction.
3. The control method according to claim 1, characterized by further comprising:
and if the primary circuit of the flyback converter works in a zero-voltage switching-on state in the current period and works in a non-zero-voltage switching-on state in the previous period, adjusting the threshold current to the positive current direction.
4. The control method according to claim 2 or 3, characterized by further comprising:
and acquiring the drain voltage of the secondary rectifier tube of the flyback converter, and judging whether the primary circuit of the flyback converter works in a zero-voltage switching-on state or not according to the drain voltage of the secondary rectifier tube of the flyback converter.
5. A control method is characterized in that the control method is applied to a primary side control circuit of a flyback converter, and comprises the following steps:
the method comprises the steps of obtaining the drain voltage of a primary side MOS tube of a flyback converter, and controlling the primary side MOS tube to be conducted when the drain voltage of the primary side MOS tube oscillates to a threshold voltage; the threshold voltage is a variable voltage value and is determined by the drain voltage of the primary side MOS tube, and a secondary side control circuit of the flyback converter controls a secondary side circuit by adopting the control method of any one of claims 1 to 4.
6. The control method according to claim 5, characterized by further comprising: if the drain voltage of the primary side MOS tube meets a zero voltage switching-on condition in the current period, setting the threshold voltage of the next period as zero voltage; otherwise, the threshold voltage of the next cycle is set to be the same as the threshold voltage of the current cycle.
7. The control method according to claim 5, characterized by further comprising:
when the working time of a primary circuit of the flyback converter in a zero-voltage opening state is greater than a time threshold, setting the threshold voltage as an initial threshold voltage, wherein the initial threshold voltage is different from the zero voltage.
8. A control circuit for controlling a primary circuit and/or a secondary circuit of a flyback converter, the control circuit comprising:
a primary side control circuit, which controls the primary side circuit of the flyback converter by adopting the control method of any one of claims 5-7; and/or
A secondary side control circuit, which controls the secondary side circuit of the flyback converter by adopting the control method of any claim 1-4.
9. A flyback converter, comprising:
a primary side circuit;
a secondary side circuit;
a primary side control circuit, which controls the primary side circuit of the flyback converter by adopting the control method of any one of claims 5-7;
a secondary side control circuit, which controls the secondary side circuit of the flyback converter by adopting the control method of any one of claims 1-4.
10. An electronic device, characterized in that the electronic device comprises the flyback converter of claim 9.
CN202110443827.XA 2021-04-23 2021-04-23 Control method, control circuit, flyback converter and electronic equipment Active CN113315378B (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109067191A (en) * 2017-12-15 2018-12-21 杰华特微电子（杭州）有限公司 Flyback power supply converter and its control method
US10218284B1 (en) * 2018-05-24 2019-02-26 Astec International Limited DC-DC power converters including a valley skipping mode and methods of operating DC-DC power converters
CN111628632A (en) * 2019-02-28 2020-09-04 立锜科技股份有限公司 Flyback power supply circuit and zero voltage switching control circuit and control method thereof
CN112054659A (en) * 2020-09-25 2020-12-08 杰华特微电子（杭州）有限公司 Zero-voltage-conduction flyback circuit and control method and control circuit thereof
CN112350581A (en) * 2020-11-02 2021-02-09 杰华特微电子（杭州）有限公司 Flyback circuit and control method and control circuit thereof

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109067191A (en) * 2017-12-15 2018-12-21 杰华特微电子（杭州）有限公司 Flyback power supply converter and its control method
US10218284B1 (en) * 2018-05-24 2019-02-26 Astec International Limited DC-DC power converters including a valley skipping mode and methods of operating DC-DC power converters
CN111628632A (en) * 2019-02-28 2020-09-04 立锜科技股份有限公司 Flyback power supply circuit and zero voltage switching control circuit and control method thereof
CN112054659A (en) * 2020-09-25 2020-12-08 杰华特微电子（杭州）有限公司 Zero-voltage-conduction flyback circuit and control method and control circuit thereof
CN112350581A (en) * 2020-11-02 2021-02-09 杰华特微电子（杭州）有限公司 Flyback circuit and control method and control circuit thereof

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