CN114884357A - Flyback converter control method and flyback converter - Google Patents

Flyback converter control method and flyback converter Download PDF

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Publication number
CN114884357A
CN114884357A CN202111615086.5A CN202111615086A CN114884357A CN 114884357 A CN114884357 A CN 114884357A CN 202111615086 A CN202111615086 A CN 202111615086A CN 114884357 A CN114884357 A CN 114884357A
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China
Prior art keywords
auxiliary
switch tube
flyback converter
main power
time
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CN202111615086.5A
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Chinese (zh)
Inventor
杨洋
黄孟意
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Joulwatt Technology Hangzhou Co Ltd
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Joulwatt Technology Hangzhou Co Ltd
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Priority to CN202111615086.5A priority Critical patent/CN114884357A/en
Publication of CN114884357A publication Critical patent/CN114884357A/en
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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
    • H02M3/33507—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 with automatic control of the output voltage or current, e.g. flyback 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
    • 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 application provides a control method for a flyback converter and the flyback converter, wherein the flyback converter comprises a main power switch tube, a transformer, a second auxiliary winding coupled with the transformer, an auxiliary switch tube connected with the second auxiliary winding and an auxiliary capacitor, and the control method is characterized by comprising the following steps of: at a first moment before the main power switch tube is switched on, switching on the auxiliary switch tube for a first time so that the main power switch tube is switched on at the lowest value of the drain-source voltage; and at the second moment after the main power switch tube is switched off, the auxiliary switch tube is switched on for the second time to charge the auxiliary capacitor.

Description

Flyback converter control method and flyback converter
Technical Field
The present invention relates to an electronic power technology, and more particularly, to a method for controlling a flyback converter and the flyback converter.
Background
Flyback converters are often used for current-isolated ac-to-dc and dc-to-dc conversion between an input and one or more outputs, and are widely used in adapters for mobile phones and notebooks due to their simple, reliable, and efficient nature. The flyback converter comprises a main power Switching tube, energy is converted by the connection and disconnection of the main power Switching tube, and in order to realize Zero Voltage Switching (ZVS) of the main power Switching tube, the flyback converter in the prior art also comprises an auxiliary Switching tube, wherein before the main power Switching tube is switched on, the auxiliary Switching tube can be switched on with proper small pulses to additionally perform reverse excitation on an excitation inductor of a transformer, and after the main power Switching tube is switched off, the ZVS of the main power Switching tube is realized by means of the energy. Therefore, the method reduces the switching loss of the main power tube by sacrificing the conduction loss of the auxiliary switching tube to a certain extent, and can be realized by using a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) with low cost and low voltage resistance by the turn ratio design of a transformer for the auxiliary switching tube.
However, the current auxiliary switching tube only carries out a method of switching on a small pulse in an open-loop or closed-loop mode in front of the main power switching tube, so that the auxiliary winding capacitor discharges to the exciting inductor, the exciting inductor reversely charges, but after the main power switching tube is switched off, the auxiliary winding capacitor needs to supplement energy, at the moment, because the auxiliary switching tube is not conducted, the auxiliary switching tube charges through the body diode to generate extra conduction loss, and particularly on occasions with high frequency, the average current passing through the body diode is relatively increased, so that the loss is further increased.
Therefore, in order to further improve the efficiency of the flyback converter, the conduction loss of the auxiliary switching tube needs to be properly reduced, and now, a control method of the flyback converter needs to be further optimized.
Disclosure of Invention
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This disclosure is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
The application aims to provide a control method of a flyback converter to meet the application occasion with strict requirements on the conduction loss of the whole system. The foregoing and other objects are achieved by the features of the independent claims. Further forms of implementation are apparent from the dependent claims, the description and the accompanying drawings, in accordance with a first aspect of the present application, there is provided a control method of a flyback converter, the flyback converter including a main power switch tube, a transformer, a second auxiliary winding coupled with the transformer, and an auxiliary switch tube and an auxiliary capacitor connected with the second auxiliary winding, the control method comprising: at a first moment before the main power switch tube is switched on, switching on the auxiliary switch tube for a first time so that the main power switch tube is switched on at the lowest value of drain-source voltage; and at a second moment after the main power switch tube is switched off, switching on the auxiliary switch tube for a second time to charge the auxiliary capacitor.
Optionally, when the flyback converter is in a critical conduction mode BCM, the first time is when an inductive current zero crossing of the flyback converter is detected; when the flyback converter is in an intermittent conduction mode DCM, the first moment is the beginning of the switching frequency of the main power switch tube.
Optionally, the first time length T GAC1 And the input voltage and the output voltage of the flyback converter meet the following conditions: t is GAC1 ＝k 1 ×V in -k 2 ×V o +T GAC1_bias Wherein V is in Is the input voltage, V o For said output voltage, T GAC1_bias Is the first minimum offset time, k 1 ，k 2 Is constant, or the first time length T GAC1 Is a fixed duration t 1 。
Optionally, the second time is a fixed time period t after the main power switch tube is detected to be turned off 2 And when the second moment is detected that the output voltage of the first auxiliary winding of the flyback converter is greater than the first threshold value, or the second moment is detected that the output voltage of the first auxiliary winding of the flyback converter is greater than the first threshold value.
Optionally, the second duration is a fixed duration t 3 。
Optionally, the second duration T GAC2 And the input voltage and the output voltage of the flyback converter meet the following conditions: t is GAC2 ＝k 3 ×V in -k 4 ×V o +T GAC2_bias Wherein V is in Is the input voltage, V o For said output voltage, T GAC2_bias Is the second minimum offset time, k 3 ，k 4 Is a constant.
Optionally, the secondThe duration and the first duration satisfy T GAC2 ＝k×T GAC1 Wherein k is a constant.
Optionally, the second time is when the drain-source voltage of the auxiliary switching tube of the flyback converter is detected to be smaller than a second threshold; and the second time duration is from the second moment to the time when the drain-source voltage of the auxiliary switching tube is detected to be greater than a third threshold value.
According to a second aspect of the present application, there is provided a flyback converter characterized by comprising: the main power switch tube is used for controlling the flyback converter to generate output voltage; the auxiliary switch tube is used for enabling the main power switch tube to be switched on at the lowest value of the drain-source voltage; and the auxiliary switching tube control circuit applies the control method to control the auxiliary switching tube.
The application provides a control method of a flyback converter and the flyback converter, and the auxiliary switch tube in the flyback converter is enabled to be in pulse conduction twice in front of and behind a main power switch tube, so that the loss of the auxiliary switch tube generated when the main power switch tube is turned off is reduced, and the efficiency of a system is improved.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present application, and those skilled in the art can obtain other drawings without inventive labor.
Fig. 1 shows a schematic diagram of a flyback converter in the prior art;
fig. 2 shows a control waveform diagram of a flyback converter in the prior art;
fig. 3 illustrates a control waveform diagram of a flyback converter according to an embodiment of the present application;
fig. 4 shows a flowchart of a control method of a flyback converter according to an embodiment of the present application;
FIG. 5 illustrates a control schematic diagram of a first turn-on of an auxiliary switch tube according to an embodiment of the present application;
FIG. 6 is a flow chart illustrating the control of the second turn-on of the auxiliary switch tube according to an embodiment of the present application;
FIGS. 7 and 8 show control diagrams of the second on-time of the auxiliary switching tube according to FIG. 6;
fig. 9 shows a control schematic diagram of the second turn-on of the auxiliary switch tube according to another embodiment of the present application.
In the following, identical reference numerals indicate identical or at least functionally identical features.
Detailed Description
Technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
For example, it should be understood that the disclosure in connection with the described method also applies to the corresponding device or system for performing the method, and vice versa. For example, if a specific method step is described, the corresponding apparatus may comprise means for performing the described method step, even if such means are not described in detail or shown in the figures. On the other hand, for example, if a specific apparatus is described on the basis of functional units, the corresponding method may comprise steps performing the described functions, even if the steps are not explicitly described or illustrated in the figures. Furthermore, it should be understood that features of the various example aspects described herein may be combined with each other, unless specifically noted otherwise.
It should be understood that, in the embodiments of the present application, a and B are connected/coupled, which means that a and B may be connected in series or in parallel, or a and B may pass through other devices, and the embodiments of the present application do not limit this.
According to the control method of the flyback converter and the flyback converter, the auxiliary switch tube is enabled to conduct the small pulse twice in front of and behind the main power switch tube, so that the conduction loss generated when the diode of the auxiliary switch tube body is conducted in front of the main power switch tube is reduced, and the efficiency of a system is improved.
Fig. 1 shows a schematic structural diagram of a prior art flyback converter, fig. 2 shows a schematic control waveform diagram of a prior art flyback converter, as shown in fig. 1, a zero-voltage-conduction flyback converter includes a main power switching tube Qp, an auxiliary switching tube Qzvs, a primary winding L1 of a transformer, a secondary winding L2, a first auxiliary winding Naux, a second auxiliary winding Nzvs, and an auxiliary capacitor C1, wherein the auxiliary switching tube Qzvs, the second auxiliary winding Nzvs, and the auxiliary capacitor C1 are connected in series, the main power switching tube and the auxiliary switching tube are field effect transistors, the first auxiliary winding Naux represents an input voltage Vin and an output voltage Vo of the flyback converter according to a turn ratio with the primary winding L1 and the secondary winding L2, a control terminal of the auxiliary switching tube Qzvs is controlled by a switch control unit 1, the switch control unit 1 is before the main power switching tube Qp is turned on, the method can reduce the switching loss of the main power switch tube Qp to a certain extent, however, after the main power switch tube Qp is turned off, the auxiliary winding capacitor C1 needs to supplement energy, at the moment, because the auxiliary switch tube Qzvs is not conducted, extra conduction loss is generated through the charging of the body diode, and particularly on the occasion of higher frequency, the loss is further increased due to the fact that the average current passing through the body diode is relatively increased.
As an example, it can be understood that by turning on the auxiliary switching tube Qzvs for the second time after the main power switching tube Qp turns off, the loss of the auxiliary switching tube Qzvs when the body diode is turned on can be reduced, and the efficiency of the whole system is improved. Fig. 3 shows a control waveform schematic diagram of an auxiliary switching tube according to an embodiment of the present application, where fig. 3(a) shows an on mode of the auxiliary switching tube Qzvs in DCM mode, and fig. 3(b) shows an on mode of the auxiliary switching tube Qzvs in CRM.
Fig. 4 is a flowchart illustrating a control method of a flyback converter according to an embodiment of the present application, where, as shown in fig. 4, the control method of the flyback converter includes steps S41-S42, and the control method of the flyback converter is used to control an auxiliary switching tube, which is coupled to a second auxiliary winding of the flyback converter, and the control method of the flyback converter can be applied to the flyback converter shown in fig. 1, for example.
In step S41, at a first time before the main power switch of the flyback converter is turned on, turning on the auxiliary switch for a first duration so that the main power switch is turned on at a lowest value of the drain-source voltage;
in step S42, the auxiliary switch is turned on for a second time period at a second time after the main power switch is turned on to charge the auxiliary capacitor.
As an example, in step S41, a first time and a first duration of the auxiliary switch tube before the main power switch tube of the flyback converter is turned on are shown in fig. 5, where fig. 5 shows a control schematic diagram of the auxiliary switch tube for the first turn-on according to an embodiment of the present application, where when the circuit is in the critical conduction mode and when the inductor current is detected to be zero, a signal is sent to enable the auxiliary switch tube to be turned on for the first duration T GAC1 When the circuit is in the discontinuous conduction mode, the switching-on frequency of the auxiliary switching tube is consistent with the self frequency of the circuit, and the first duration T GAC1 The first time period T is set in relation to the input voltage Vin and the output voltage Vo GAC1 And the input voltage and the output voltage of the flyback converter meet the following conditions: t is GAC1 ＝k 1 ×V in -k 2 ×V o +T GAC1_bias Wherein V is in For input voltage, V o To output a voltage, T GAC1_bias Is the first minimum offset time, k 1 ，k 2 As a constant, the auxiliary switch tube is turned on for a first time period T GAC1 And then shut down.
It will be appreciated that the above description only describes the auxiliary switching tubeAn embodiment of one time of opening, however, the embodiments of the present application are not limited thereto, and there may be other manners of extension and modification, for example, the first duration T GAC1 Can be set to a fixed duration t 1 。
As an example, in step S42, the auxiliary switch tube is turned on for a second time after the main power switch tube of the flyback converter is turned on, and the second turn-on logic of the auxiliary switch tube is as shown in fig. 6-8, fig. 6 shows a control flow chart of the auxiliary switch tube for the second turn-on according to the embodiment of the present application, wherein when the auxiliary switch tube Qzvs starts to be turned on for the second time, the circuit may detect that the main power switch tube is turned off for Td time, and then send a signal to enable the auxiliary switch tube to perform the second turn-on, or, when the circuit detects that the voltage Vs output by the first auxiliary winding exceeds zero, send a signal to enable the auxiliary switch tube to perform the second turn-on, it can be understood that the output voltage Vs of the first auxiliary winding is a theoretical value, and in practical applications, a turn-on condition is triggered when the output voltage of the first auxiliary winding is detected to be greater than the first threshold value, as an example, the first threshold may be 0-200 mV; or when the circuit detects that the drain-source voltage Vzvs of the auxiliary switch tube Qzvs is smaller than the second threshold value, the circuit sends a signal to enable the auxiliary switch tube to perform a second switching-on action. After the auxiliary switch tube Qzvs is conducted, timing T GAC2 And then, sending a signal to enable the auxiliary switch tube to perform a second turn-off action, or outputting a signal to enable the auxiliary switch tube to perform a second turn-off action when the circuit detects that the drain-source voltage Vzvs of the auxiliary switch tube Qzvs is greater than a third threshold value.
It can be understood that, the above describes the method for determining whether to send the second turn-on signal and the second turn-off signal, and the condition detection for controlling the turn-on and turn-off time of the auxiliary switching tube may be arbitrarily selected and combined, without limiting a certain matching relationship.
FIGS. 7 and 8 are schematic diagrams illustrating the control of the second turn-on period of the auxiliary switch tube according to FIG. 6, wherein the auxiliary switch tube is turned on for a second time period T as shown in FIG. 7 GAC2 Then is turned off, wherein the second duration T GAC2 With flyback convertersThe input voltage and the output voltage satisfy: t is GAC2 ＝k 3 ×V in -k 4 ×V o +T GAC2_bias Wherein V is in For input voltage, V o To output a voltage, T GAC2_bias Is the second minimum offset time, k 3 ，k 4 Is a constant. Alternatively, as another example, as shown in FIG. 8, the second duration may be directly proportional to the first duration, and the second duration T may be proportional to the first duration GAC2 And the first time length T GAC1 Satisfy T GAC2 ＝k×T GAC1 Wherein k is a constant.
It is understood that the above describes only one embodiment of the auxiliary switch tube at the second turn-on time, however, the embodiments of the present application are not limited thereto, and there may be other extensions and variations, for example, the second time period T GAC2 Can be set to a fixed duration t 2 。
As an example, fig. 9 shows a structure diagram of a control circuit for turning on the auxiliary switch tube for the second time according to an embodiment of the present application, such a method for setting the pulse width needs to detect the drain-source voltage Vzvs of the auxiliary switch tube Qzvs, and the second time of the second turning on may be that when the drain-source voltage Vzvs of the auxiliary switch tube Qzvs is detected to be smaller than a second threshold, a signal is sent to enable the auxiliary switch tube Qzvs to be turned on, since the conduction voltage drop of the body diode of the auxiliary switch tube Qzvs is usually-700 mV, as an embodiment, the second threshold may be-200 mV-0; when the drain-source voltage Vzvs of the auxiliary switching tube Qzvs is detected to be zero, a signal is sent to enable the auxiliary switching tube Qzvs to be turned off, it can be understood that the zero crossing of the drain-source voltage is a theoretical value, and in practical application, a turn-off condition is triggered when the drain-source voltage of the auxiliary switching tube Qzvs is detected to be greater than a third threshold, where the third threshold may be 0-20mV as an embodiment. As shown in fig. 9, the control circuit of the auxiliary switch tube includes a first comparator, a second comparator and a trigger, wherein a first input end of the first comparator receives the second threshold, a second input end of the first comparator receives the drain-source voltage of the auxiliary switch tube Qzvs, an output end of the first comparator outputs a signal to the trigger as a second turn-on signal, a second input end of the second comparator receives the third threshold, a first input end of the first comparator receives the drain-source voltage of the auxiliary switch tube Qzvs, and an output end of the second comparator outputs a signal to the trigger as a second turn-off signal.
It can be understood that, the above describes the control method for the first turn-on and the control method for the second turn-on of the auxiliary switch tube, and the two control methods can be arbitrarily selected and combined to control the turn-on and the turn-off of the auxiliary switch tube, without limiting a certain collocation relationship.
According to a second aspect of the present application, there is also provided a flyback converter including: the main power switch tube is used for controlling the flyback converter to generate output voltage; the auxiliary switching tube is used for realizing zero voltage switching-on of the main power switching tube; and the auxiliary switching tube control circuit applies the control method to control the auxiliary switching tube.
As one example, the auxiliary switching tube control circuit includes a first on control circuit and a second on control circuit, wherein the first on control circuit includes a first on signal generation circuit configured to generate a first on signal, a first off signal generation circuit configured to generate a first off signal, a first control signal generation circuit configured to receive the first on signal and the first off signal to generate a first control signal to control the auxiliary switching tube; the second on-control circuit comprises a second on-signal generating circuit configured to generate a second on-signal, a second off-signal generating circuit configured to generate a second off-signal, and a second control signal generating circuit configured to receive the second on-signal and the second off-signal to generate a second secondary control signal for controlling the auxiliary switching tube. It is understood that the first on signal may be generated according to the detected inductor current, and the first off signal may be generated by receiving the input voltage and the output voltage, generating with a timer according to the offset time, or directly setting the fixed time; similarly, the second turn-on signal may be generated according to the voltage of the detection auxiliary winding, or generated after the detection main power switch tube is turned off for a certain time, or the second turn-on signal may also be generated by detecting that the drain-source voltage of the detection auxiliary switch tube is smaller than the second threshold, the second turn-off signal may be in a direct proportion to the timing time of the first turn-off signal, or may be generated by receiving the input voltage and the output voltage, the principle is the same as that of the generation of the first turn-off signal, and details are not repeated here, and the second turn-off signal may also be generated by detecting the zero crossing of the drain-source voltage of the detection auxiliary switch tube.
It is understood that the above describes only one embodiment of the auxiliary switching tube control circuit of the flyback converter, however, the embodiments of the present application are not limited thereto, and there may be other extensions and modifications.
Any range or device value given herein may be extended or modified without loss of the effect sought. Moreover, any embodiment may be combined with another embodiment that is not explicitly prohibited.
Although the subject matter has been described in language specific to structural features and/or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as examples of implementing the claims, and other equivalent features and acts are intended to fall within the scope of the claims.
It is to be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. Embodiments are not limited to embodiments that solve any or all of the problems or embodiments having any or all of the benefits and advantages described. It should also be understood that reference to "an" item may refer to one or more of those items.
The steps of the methods described herein may be performed in any suitable order, or simultaneously where appropriate. Moreover, individual blocks may be deleted from any of the methods without departing from the spirit and scope of the subject matter described herein. Aspects of any of the embodiments described above may be combined with aspects of any of the other embodiments described to form further embodiments without sacrificing the sought after effect.
The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
It should be understood that the above description is given by way of example only and that various modifications may be made by those skilled in the art. The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this disclosure.

Claims (9)

1. A control method of a flyback converter comprises a main power switch tube, a transformer, a second auxiliary winding coupled with the transformer, and an auxiliary switch tube and an auxiliary capacitor which are connected with the second auxiliary winding, and is characterized in that the control method comprises the following steps:
turning on the auxiliary switch tube for a first time at a first moment before the main power switch tube is turned on, so that the main power switch tube is turned on at the lowest value of drain-source voltage;
and at a second moment after the main power switch tube is switched off, switching on the auxiliary switch tube for a second time to charge the auxiliary capacitor.
2. The control method according to claim 1, wherein when the flyback converter is in a critical conduction mode (BCM), the first time is when a zero crossing of an inductor current of the flyback converter is detected;
when the flyback converter is in an intermittent conduction mode DCM, the first moment is the beginning of one cycle of the main power switch tube switch.
3. Control method according to claim 1, characterized in that said first time length T GAC1 And the input voltage and the output voltage of the flyback converter meet the following conditions:
T GAC1 ＝k 1 ×V in -k 2 ×V o +T GAC1_bias
wherein, V in Is the input voltage, V o For said output voltage, T GAC1_bias Is the first minimum offset time, k 1 ，k 2 Is a constant, or alternatively,
the first duration T GAC1 Is a fixed duration t 1 。
4. The control method of claim 1, wherein the second time is a fixed time period t after the main power switch is detected to be turned off 2 In the course of time, or alternatively,
the second moment is when the output voltage of the first auxiliary winding of the flyback converter is detected to be larger than a first threshold value.
5. The control method of claim 1, wherein the second period is a fixed period t 3 。
6. Control method according to claim 1, characterized in that said second duration T GAC2 And the input voltage and the output voltage of the flyback converter meet the following conditions:
T GAC2 ＝k 3 ×V in -k 4 ×V o +T GAC2_bias
wherein, V in Is the input voltage, V o For said output voltage, T GAC2_bias Is the second minimum offset time, k 3 ，k 4 Is a constant.
7. The control method according to claim 1, whichCharacterized in that the second duration and the first duration satisfy T GAC2 ＝k×T GAC1 Wherein k is a constant.
8. The control method according to claim 1, wherein the second time is when a drain-source voltage of an auxiliary switching tube of the flyback converter is detected to be less than a second threshold;
and the second time duration is from the second moment to the time when the drain-source voltage of the auxiliary switch tube is detected to be greater than a third threshold value.
9. A flyback converter, comprising:
the main power switch tube is used for controlling the flyback converter to generate output voltage;
the auxiliary switch tube is used for enabling the main power switch tube to be switched on at the lowest value of drain-source voltage;
an auxiliary switching tube control circuit applying the control method of claims 1-8 to control the auxiliary switching tube.
CN202111615086.5A 2021-12-27 2021-12-27 Flyback converter control method and flyback converter Pending CN114884357A (en)

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Application Number Priority Date Filing Date Title
CN202111615086.5A CN114884357A (en) 2021-12-27 2021-12-27 Flyback converter control method and flyback converter

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Application Number Priority Date Filing Date Title
CN202111615086.5A CN114884357A (en) 2021-12-27 2021-12-27 Flyback converter control method and flyback converter

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Publication Number Publication Date
CN114884357A true CN114884357A (en) 2022-08-09

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