CN114039487A

CN114039487A - Asymmetric half-bridge flyback converter and control method thereof

Info

Publication number: CN114039487A
Application number: CN202110842917.6A
Authority: CN
Inventors: 许祥勇
Original assignee: Joulwatt Technology Co Ltd
Current assignee: Joulwatt Technology Co Ltd
Priority date: 2021-07-26
Filing date: 2021-07-26
Publication date: 2022-02-11

Abstract

The invention discloses an asymmetric half-bridge flyback converter and a control method thereof, wherein the control method comprises the following steps in each switching period: sampling a preset parameter of the asymmetric half-bridge flyback converter during the conduction period of the first switch tube to obtain a first sampling signal; sampling a predetermined parameter during the first conduction period of the second switching tube to obtain a second sampling signal; and comparing the magnitude of the first sampling signal with that of the second sampling signal, and controlling the second switching tube to be switched on again for the first time under the condition that the comparison result meets the requirement, otherwise, controlling the second switching tube to be switched on once in the current switching period. According to the invention, a certain judgment condition is set to determine whether the asymmetric half-bridge flyback converter needs to turn on the second switching tube twice in one switching period, so that the asymmetric half-bridge flyback converter has better working efficiency under different application conditions.

Description

Asymmetric half-bridge flyback converter and control method thereof

Technical Field

The invention relates to the technical field of asymmetric half-bridge flyback converters, in particular to an asymmetric half-bridge flyback converter and a control method thereof.

Background

With the rapid development of the power electronic field, the application of the switching converter is more and more extensive, and especially, people put forward more requirements on the switching converter with high power density, high reliability and small volume. The conventional low-power switch converter is realized by adopting a flyback topology, and has the advantages of simple structure, low cost and the like; however, the common flyback topology is a hard switch and leakage inductance energy cannot be recovered, so that the efficiency and the volume of the medium-small power converter are limited. In order to meet the trend of miniaturization, light weight and modularization of power converters, soft switching technology has become one of the hot spots of power electronic technology. The 'soft switch' refers to Zero Voltage Switch (ZVS) or zero current switch, which uses resonance principle to make the switch tube voltage (or current) of switch converter change according to sine (or quasi-sine) rule, when the voltage crosses zero, the device is switched on (or the current naturally crosses zero, the device is switched off), the switch loss is zero, thus the efficiency and switch frequency of converter are improved, and the volume of transformer and inductor is reduced. Although soft switching technology enables miniaturization, modularization, etc. of power converters, many circuits, such as LLC, become very complex, increasing the cost of medium and low power converters, often to the detriment of commercial competition. While an Asymmetric half-bridge flyback Converter (AHB) has two switches on the primary side of the transformer, which may be provided in a half-bridge configuration and driven by different Pulse Width Modulation (PWM) signals for the two switches. The inductor of an asymmetric half-bridge flyback converter is split to form a transformer so that the voltage is multiplied over the transformer-based winding ratio, with the added advantage of isolation. Meanwhile, zero-voltage switching-on of the two switching tubes can be realized under the condition that the number and complexity of devices of the common flyback converter are close, leakage inductance energy is recycled, self-driven synchronous rectification is easy to realize, the size of the transformer is reduced while the efficiency is effectively improved, and the method becomes a better application scheme.

The circuit diagram of the conventional asymmetric half-bridge flyback converter is shown in fig. 1a and 1b, wherein in fig. 1a, the upper switch tube Q2 is the second switch tube, and the lower switch tube Q1 is the first switch tube; in fig. 1b, the upper switch tube Q1 is the first switch tube, and the lower switch tube Q2 is the second switch tube, and the two circuits basically have the same working principle, except that the winding positions are different. Taking fig. 1b as an example, the operating waveforms of the semiconductor device operating in the discontinuous mode (DCM mode) are as shown in fig. 2, and Vgs _ Q1 and Vgs _ Q2 are the first switching tube Q1 and the second switching tube Q, respectively2, a driving voltage signal waveform; i.e. i_LmIs the waveform of the exciting current on the primary winding Np; vaux is the voltage across the auxiliary winding Na; vds _ Q1 is the drain-source voltage of the first switch tube. In order to prevent the first switch Q1 and the second switch Q2 from being shared, a certain dead time is required to be left in the driving voltage signals supplied to the first switch Q1 and the second switch Q2.

Referring to fig. 2, in order to implement Zero Voltage Switching (ZVS) of the asymmetric half-bridge flyback converter in the DCM mode, the second switching tube Q2 needs to be additionally turned on once in each switching period, and a negative excitation current is generated at the primary side portion of the asymmetric half-bridge flyback converter by additionally turning on the second switching tube Q2 for a period of time (corresponding to a time period t4-t5), so as to implement zero voltage switching of the first switching tube Q1. However, when the existing scheme realizes zero-voltage switching-on of the first switching tube Q1, the performance is not sufficiently optimized, and the two aspects are mainly shown as follows:

1. in order to optimize efficiency, the second switch tube Q2 needs to be turned on again at the resonant oscillation peak of the drain-source voltage Vds _ Q1 of the first switch tube, but because the input voltage Vin of the system has disturbance such as power frequency ripple, the phenomenon of switching the number of resonant oscillation cycles in a steady state exists, and the problem of audio noise is caused.

2. When the load is light, the resonance oscillation can be damped to be nearly absent, at the moment, the drain-source voltage Vds _ Q1 of the first switch tube is close to Vi-N Vo, and in the application that the input voltage Vin is low and the output voltage Vo is high, the second switch tube Q2 is additionally turned on once, so that the optimization of the system efficiency is not facilitated, and the system efficiency is even deteriorated.

Therefore, there is a need to provide an improved technical solution to overcome the above technical problems in the prior art.

Disclosure of Invention

In order to solve the technical problem, the invention provides an asymmetric half-bridge flyback converter and a control method thereof, wherein a certain judgment condition is set to determine whether the asymmetric half-bridge flyback converter in the DCM mode needs to turn on the second switching tube twice in one switching period, so that the asymmetric half-bridge flyback converter has better working efficiency under different application conditions.

According to a first aspect of the present disclosure, there is provided a control method for an asymmetric half-bridge flyback converter, the asymmetric half-bridge flyback converter including a first switching tube and a second switching tube constituting a half bridge, a transformer and a controller, the control method including, in each switching cycle:

sampling a first preset parameter of the asymmetric half-bridge flyback converter during the conduction period of the first switch tube to obtain a first sampling signal;

sampling a second preset parameter of the asymmetric half-bridge flyback converter during the first conduction period of the second switching tube to obtain a second sampling signal;

and comparing the magnitude of the first sampling signal with that of the second sampling signal, and controlling the second switching tube to be additionally switched on for the first time under the condition that the comparison result meets the requirement, otherwise, controlling the second switching tube to be switched on once in the current switching period.

Optionally, the asymmetric half-bridge flyback converter operates in discontinuous mode.

Optionally, the transformer includes a primary winding, a secondary winding, and an auxiliary winding, the first predetermined parameter and the second predetermined parameter are voltages at two ends of any winding in the transformer, and the comparison result is a comparison operation result of an absolute value of the first sampling signal and an absolute value of the second sampling signal.

Optionally, in order to satisfy the requirement when the comparison result is that the absolute value of the first sampled signal is greater than the product of the absolute value of the second sampled signal and k1,

wherein the value range of k1 is 0.5-5.

Optionally, when the comparison result is that the difference between the absolute value of the first sampling signal and the absolute value of the second sampling signal is greater than a is satisfied,

wherein the value range of a is larger than zero.

Optionally, the first predetermined parameter and the second predetermined parameter are both voltages across the auxiliary winding.

Optionally, the first predetermined parameter and the second predetermined parameter are both currents flowing through a voltage detection pin of a controller of the asymmetric half-bridge flyback converter, the comparison result is a comparison operation result of an absolute value of the first sampling signal and an absolute value of the second sampling signal,

the voltage detection pin of the controller is connected with one end of an auxiliary winding in the transformer through a resistance element, and the other end of the auxiliary winding is connected with a reference ground.

Optionally, in order to satisfy the requirement when the comparison result is that the absolute value of the first sampled signal is greater than the product of the absolute value of the second sampled signal and k2,

wherein the value range of k2 is 0.5-5.

Optionally, the first predetermined parameter is the on-time of the first switch tube, the second predetermined parameter is the first on-time of the second switch tube, and the comparison result is that the first sampling signal is smaller than the product of the second sampling signal and k3,

wherein the value range of k3 is 0.5-5.

Optionally, after controlling the second switching tube to be additionally turned on for a first time, the control method further includes:

and judging whether the first switching tube is switched on at zero voltage in the next switching period, if so, reducing the first time by a first step time, otherwise, increasing the first time by a second step time.

Optionally, reducing the first time by a first further duration comprises:

and delaying a turn-off signal for controlling the turn-off of the second switch tube for a first overlap subtraction time, and then providing the delayed turn-off signal to a control end of the second switch tube, wherein the first overlap subtraction time is the difference between the first time and the first step duration.

Optionally, increasing the first time by a second step length comprises:

and delaying a turn-off signal for controlling the turn-off of the second switching tube for a first superposition time, and then providing the delayed turn-off signal to a control end of the second switching tube, wherein the first superposition time is the sum of the first time and the second stepping time.

According to a second aspect of the present disclosure, there is provided another control method for an asymmetric half-bridge flyback converter, the asymmetric half-bridge flyback converter including a first switching tube and a second switching tube forming a half bridge, a transformer and a controller, the control method including:

sampling output voltage information of the asymmetric half-bridge flyback converter during the first conduction period of the second switching tube to obtain a first sampling signal;

and comparing the first sampling signal with the voltage threshold, and controlling the second switching tube to be switched on again for the first time under the condition that the comparison result meets the requirement, otherwise, controlling the second switching tube to be switched on once in the current switching period.

Optionally, when the first sampling signal is greater than the voltage threshold, the second switching tube is turned on again for the first time, and otherwise, the second switching tube is controlled to be turned on once in the current switching period.

Optionally, the transformer includes a primary winding, a secondary winding, and an auxiliary winding, and the voltage across any one of the windings in the transformer is sampled to obtain the first sampling signal.

According to a third aspect of the present disclosure, there is provided an asymmetric half-bridge flyback converter operating in discontinuous mode, the asymmetric half-bridge flyback converter comprising:

a transformer including a primary winding, a secondary winding, and an auxiliary winding;

the first switching tube and the second switching tube are connected between the input voltage input end and the reference ground in series;

the excitation inductor is connected between the drain electrode of the second switching tube and the same-name end of the primary winding in the transformer;

a first capacitor connected between a reference ground and a synonym terminal of the primary winding; and

a controller respectively connected with the first switch tube and the second switch tube,

wherein the controller includes:

the first control unit is configured to sample a first predetermined parameter of the asymmetric half-bridge flyback converter during the conduction period of the first switching tube and sample a second predetermined parameter of the asymmetric half-bridge flyback converter during the first conduction period of the second switching tube, and the first control unit is further configured to compare the two sampling results and control the conduction times of the second switching tube in one switching period according to the comparison result.

A second control unit configured to provide a driving signal for controlling the first switching tube to be turned on/off.

Optionally, the first predetermined parameter and the second predetermined parameter are both voltages across any winding in the transformer.

Optionally, the first predetermined parameter and the second predetermined parameter are both voltages across the auxiliary winding, and the asymmetric half-bridge flyback converter further includes:

the voltage detection circuit comprises a first resistor and a second resistor which are connected between a first end and a second end of the auxiliary winding in series, and a connection node of the first resistor and the second resistor is connected with a voltage detection pin of the controller.

Optionally, the first predetermined parameter and the second predetermined parameter are both currents flowing through a voltage detection pin of a controller of the asymmetric half-bridge flyback converter, and the asymmetric half-bridge flyback converter further includes:

the third resistor is connected between a voltage detection pin of the controller and a first end of an auxiliary winding in the transformer, and a second end of the auxiliary winding is connected with a reference ground;

the third switching tube is connected between the voltage detection pin of the controller and the reference ground;

and the third control unit is connected with the control end of the third switching tube and used for controlling the third switching tube to be switched on during the switching-on period of the first switching tube and the second switching tube.

Optionally, the first predetermined parameter is a turn-on time of the first switching tube, and the second predetermined parameter is a first turn-on time of the second switching tube.

Optionally, the first control unit further comprises:

controlling the second switch tube to be conducted twice in the current switching period under the condition that the comparison result meets the requirement, recording the second conduction time as the first time,

the requirement is satisfied when the absolute value of the sampled signal of the first predetermined parameter is greater than the product of the absolute value of the sampled signal of the second predetermined parameter and K1 or is satisfied when the absolute value of the sampled signal of the first predetermined parameter is greater than the product of the absolute value of the sampled signal of the second predetermined parameter and K2, wherein K1 and K2 are both in the range of 0.5 to 5.

Optionally, the controller further comprises:

an adaptive adjustment unit configured to adaptively adjust the magnitude of the first time according to the turn-on condition of the second switching tube in a next switching period of a specific switching period of the asymmetric half-bridge flyback converter,

wherein the second switch tube is conducted twice in each specific switch period.

The invention has the following beneficial effects:

1. in each switching period in the DCM mode, by comparing an absolute value of a predetermined parameter of the asymmetric half-bridge flyback converter during the conduction period of the main switch with an absolute value of a predetermined parameter of the asymmetric half-bridge flyback converter during the conduction period of the second switching tube, it can be accurately determined whether the asymmetric half-bridge flyback converter in the DCM mode needs to turn on the second switching tube twice in one switching period, and further, a deterioration influence of additionally turning on the second switching tube once again in an application where a load is light, an input voltage is low, and an output voltage is high on a system efficiency can be avoided, so that the asymmetric half-bridge flyback converter can have better working efficiency when realizing zero-voltage turning on under different application conditions.

2. And a hiccup mode is also arranged between the BCM mode (critical mode) and the DCM mode, so that the second turn-on times of the second switching tube appearing in every N switching periods can be reduced, and the system efficiency is further optimized.

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 shows a schematic circuit diagram of an asymmetric half-bridge flyback converter in the prior art;

fig. 1b shows a schematic circuit diagram of another asymmetric half-bridge flyback converter in the prior art;

fig. 2 shows a timing waveform diagram of a conventional asymmetric half-bridge flyback converter in discontinuous mode (DCM mode);

fig. 3 shows a schematic circuit diagram of an asymmetric half-bridge flyback converter provided according to a first embodiment of the present disclosure;

fig. 4 shows a schematic circuit diagram of an asymmetric half-bridge flyback converter provided according to a second embodiment of the present disclosure;

fig. 5 illustrates a timing waveform diagram of an asymmetric half-bridge flyback converter provided according to an embodiment of the present disclosure in discontinuous mode (DCM mode);

fig. 6 shows a flowchart of a control method of an asymmetric half-bridge flyback converter provided according to an embodiment of the present disclosure.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

The present invention will be described in detail below with reference to the accompanying drawings.

As shown in fig. 3 and 4, in the present disclosure, an asymmetric half-bridge flyback converter includes: the transformer TR comprises a primary winding Np, a secondary winding Ns and an auxiliary winding Na, a first switching tube Q1 and a second switching tube Q2 which form a half bridge, an excitation inductor Lm, a first capacitor Cr and a controller 100.

The drain of the first switch tube Q1 is connected to the input end of the input voltage Vin, and the gate of the first switch tube Q1 is connected to the controller 100; the drain of the second switch Q2 is connected to the source of the first switch Q1, the source of the second switch Q2 is connected to ground, the gate of the second switch Q2 is connected to the controller 100, and the capacitors C1 and C2 are junction capacitors of the first switch Q1 and the second switch Q2, respectively. In the same switching period, the first switching tube Q1 and the second switching tube Q2 are turned on in time-sharing mode to transfer the input voltage Vin from the primary side portion to the secondary side portion of the transformer TR. In one possible embodiment, the first switching transistor Q1 and the second switching transistor Q2 are both NMOS field effect transistors.

One end of the excitation inductor Lm is connected with the drain electrode of the second switching tube Q2, and the other end of the excitation inductor Lm is connected with the dotted end of the primary winding Np; one end of the first capacitor Cr is connected to the synonym end of the primary winding Np, and the other end of the first capacitor Cr is connected to the reference ground. In this embodiment, the first capacitor Cr is a resonant capacitor.

The secondary side part of the asymmetric half-bridge flyback converter comprises: a rectifier diode D1 and an output capacitor Co. The anode of the rectifier diode D1 is connected with the synonym terminal of the secondary winding Ns, and the cathode of the rectifier diode D1 is connected with the output terminal of the asymmetric half-bridge flyback converter; the positive pole of the output capacitor Co is connected with the output end of the asymmetric half-bridge flyback converter, the negative pole of the output capacitor Co is connected with the reference ground, and meanwhile, the dotted terminal of the secondary winding Ns is also connected with the reference ground. Further, the output terminal of the asymmetric half-bridge flyback converter is connected to a load, and the load receives the electric energy (such as voltage and current) converted by the asymmetric half-bridge flyback converter. In some examples, the power converted by the asymmetric half-bridge flyback converter also passes through a filter before reaching the load. In some examples, the filter is a subcomponent of the asymmetric half-bridge flyback converter, an external component of the asymmetric half-bridge flyback converter, and/or a subcomponent of the load. In any case, the load may perform a function using filtered or unfiltered power from the asymmetric half-bridge flyback converter. Alternatively, the load may include, but is not limited to, a computing device and associated components, such as a microprocessor, electrical components, circuitry, laptop computer, desktop computer, tablet computer, mobile phone, battery, speaker, lighting unit, automotive/marine/aeronautical/train associated components, motor, transformer, or any other type of electrical device and/or circuitry that receives a voltage or current from a flyback converter.

The controller 100 includes: a first control unit 110, a second control unit 120 and an adaptive adjustment unit 130. The second control unit 120 is connected to the gate of the first switch Q1, the first control unit 110 is connected to the gate of the second switch Q2, and the adaptive adjustment unit 130 is connected to the auxiliary winding Na via the voltage detection pin Vs of the controller 100.

The first control unit 110 is configured to sample a first predetermined parameter of the asymmetric half-bridge flyback converter during the turn-on period of the first switching tube Q1, and sample a second predetermined parameter of the asymmetric half-bridge flyback converter during the first turn-on period of the second switching tube Q2, and the first control unit 110 is further configured to compare the two sampling results and control the turn-on times of the second switching tube Q2 in one switching period according to the comparison result.

For example, a sample-and-hold unit, a sampling unit, and a comparison unit may be provided in the first control unit 110.

When the asymmetric half-bridge flyback converter is determined to operate in the discontinuous mode (DCM mode), the sample-and-hold unit is configured to sample and hold a first predetermined parameter of the asymmetric half-bridge flyback converter during a conducting period of the first switching tube Q1 in each switching period in the DCM mode, and obtain a first sampling signal according to a sampling result.

The sampling unit is used for sampling a second preset parameter of the asymmetric half-bridge flyback converter during the first conduction period of the second switching tube and obtaining a second sampling signal according to a sampling result.

The comparing unit is respectively connected to the sample-and-hold unit and the sampling unit, and is configured to receive the second sampling signal and the held first sampling signal, compare the first sampling signal with the second sampling signal, and trigger the first control unit 110 to control the second switching tube Q2 to be turned on twice in the current switching period if the comparison result meets the requirement, that is, the second switching tube Q2 is turned on for the first time after the preset time when the second switching tube Q2 is turned off for the first time; or in case the comparison result does not meet the requirement, the first control unit 110 is triggered to control the second switching tube Q2 to be turned on only once in the current switching period.

It is understood that the first predetermined parameter and the second predetermined parameter of the asymmetric half-bridge flyback converter may be the same or different. For example, based on the operation principle of the transformer TR, the voltage across the primary winding Np, the voltage across the secondary winding Ns, and the voltage Vaux across the auxiliary winding Na in the transformer TR all have a certain proportional relationship. Furthermore, in some embodiments, the first predetermined parameter and the second predetermined parameter of the asymmetric half-bridge flyback converter are both voltages across any winding of the transformer TR, wherein the voltages across the auxiliary winding Na are preferred. At this time, the comparison result of the comparison unit in the first control unit 110 on the first sampling signal and the second sampling signal is the comparison operation result on the absolute value of the first sampling signal and the absolute value of the second sampling signal. Exemplarily, taking a predetermined parameter as an example of the voltage across the auxiliary winding Na, in this case, referring to fig. 3, the asymmetric half-bridge flyback converter further includes: a first resistor R1 and a second resistor R2. The first resistor R1 and the second resistor R2 are sequentially connected in series between the different-name end and the same-name end of the auxiliary winding Na, and a connection node of the first resistor R1 and the second resistor R2 is connected to a voltage detection pin Vs of the controller 100.

Alternatively, in this embodiment, the voltage across the auxiliary winding Na may be sampled by the voltage detection pin Vs of the controller 100 after being divided by the first resistor R1 and the second resistor R2. Alternatively, the controller 100 may directly sample the voltage across the auxiliary winding Na.

Further, in this embodiment, after the comparison by the comparison unit, if the absolute value of the first sampling signal (denoted as Vaux1) is greater than the product of the absolute value of the second sampling signal (denoted as Vaux2) and k1, that is, Vaux1> k1 × Vaux2, or if the difference between the absolute value of the first sampling signal Vaux1 and the absolute value of the second sampling signal Vaux2 is greater than a, the comparison unit triggers the first control unit 110 to control the second switching tube Q2 to be turned on twice in the current switching period; if the absolute value of the first sampling signal is less than or equal to the product of the absolute value of the second sampling signal and k1, i.e. Vaux1 is less than or equal to k1 × Vaux2, or if the difference between the absolute value of the first sampling signal Vaux1 and the absolute value of the second sampling signal Vaux2 is less than or equal to a, the comparing unit triggers the first control unit 110 to control the second switch Q2 to be turned on only once in the current switching period. Wherein, the value range of k1 is 0.5 to 5, and the value range of a is larger than zero.

Referring to fig. 5, the operation principle of the asymmetric half-bridge flyback converter in the DCM mode in one switching period is as follows:

in the time period from t0 to t1, the second driving signal Vgs _ Q1 is at a high level, and the first switch Q1 is turned on. In the time period, the energy at the input end of the input voltage Vin is excited to the transformer TR through a loop of the first switching tube Q1, the excitation inductor Lm, the primary winding Np and the first capacitor Cr, and the excitation current i_LmFirst decreasing linearly from negative to zero and then increasing linearly. In the process, the excitation inductor Lm, the transformer TR and the first capacitor Cr store energy, and the secondary rectifier diode D1 is turned off in the negative direction.

Meanwhile, during this period, the sample-and-hold unit in the first control unit 110 sample-and-hold the voltage across the auxiliary winding Na, and thus obtains a first sample signal.

At time t1, the second driving signal Vgs _ Q1 goes low and the first switching transistor Q1 is turned off.

During the period t1-t2, the first switch tube Q1 is in the off state, and the second switch tube Q2 is not turned on, which is the dead time. In the dead time, because the excitation inductor Lm and the primary winding Np follow current, the junction capacitor C1 of the first switching tube Q1, the junction capacitor C2 of the second switching tube Q2, the first capacitor Cr, the excitation inductor Lm and the primary winding Np resonate to extract energy of the junction capacitor C2 of the second switching tube Q2, so that the drain-source voltage Vds _ Q2 of the second switching tube Q2 decreases, the junction capacitor C1 of the first switching tube Q1 is charged at the same time, and the drain-source voltage Vds _ Q1 of the first switching tube Q1 increases. At the same time, the voltage Vaux on the auxiliary winding Na rises from the negative voltage during this time period.

At time t2, the junction capacitor voltage of the first switch Q1 reaches the highest, the junction capacitor voltage of the second switch Q2 is pulled to zero, the first driving signal Vgs _ Q2 becomes high, the second switch Q2 is turned on, and the zero-voltage turn-on of the second switch Q2 can be realized. At the same time, the voltage Vaux over the auxiliary winding Na also reaches a maximum.

In the time period from t2 to t3, in the secondary side part of the asymmetric half-bridge flyback converter, the rectifier diode D1 is conducted in the forward direction, the energy stored in the primary side of the transformer TR begins to be released to the secondary side, and the exciting current i_LmThe linearity decreases.

Meanwhile, during this period, the sampling unit in the first control unit 110 samples the voltage across the auxiliary winding Na, and thus obtains a second sampling signal.

At time t3, the first control unit 110 controls the second switch tube Q2 to turn off for the first time. Meanwhile, at time t3, excitation current i_LmLinearly down to near zero current.

In the time period from t3 to t4, the first switch tube Q1 and the second switch tube Q2 are both in an off state. During the time period, the junction capacitor C1 of the first switch tube Q1, the junction capacitor C2 of the second switch tube Q2, the first capacitor Cr, the excitation inductor Lm and the primary winding Np resonate, and a resonant waveform is generated between the drain and source electrodes of the first switch tube Q1 and across the auxiliary winding Na.

Meanwhile, after time t3, the sample-and-hold unit and the sampling unit in the first control unit 110 respectively transmit the first sampling signal and the second sampling signal obtained by respective sampling to the comparison unit for comparison, and output corresponding comparison results.

Further, if the comparison result output by the comparison unit does not meet the requirement, in the current switching cycle, triggering a timing circuit in the asymmetric half-bridge flyback converter to start timing at a zero-crossing detection time (ZCD) when the voltage Vaux on the auxiliary winding Na drops to zero, stopping timing when the timing duration of the timing circuit reaches a duration corresponding to a preset third time Td, and triggering the second control unit 120 to output a second driving signal Vgs _ Q1 with a high level when timing is finished, so as to control the first switching tube Q1 to be turned on and start a new switching cycle.

If the comparison result output by the comparison unit meets the requirement, the first control unit 110 is triggered to output the first driving signal Vgs _ Q2 at the high level again at time t4 in the current switching cycle to control the second switching transistor Q2 to be additionally turned on again. Meanwhile, the timing circuit in the asymmetric half-bridge flyback converter starts timing from the time t 4.

In the time period from t4 to t5, the second switching tube Q2 is in a conducting state, and since the excitation inductor Lm and the first capacitor Cr resonate, the energy stored in the first capacitor Cr is also released to the secondary side through the forward process, and the excitation current i_LmGo into the negative direction.

At the time t5, the timing duration of the timing circuit reaches the duration corresponding to the preset first time and stops timing. Meanwhile, the first control unit 110 is triggered to output the first driving signal Vgs _ Q2 of a low level when the timing is stopped to control the second switching tube Q2 to turn off for the second time.

In the time period from t5 to t6, the first switch tube Q1 and the second switch tube Q2 are both in an off state because of the excitation current i_LmThe excitation inductor Lm and the primary winding Np follow current, so that the junction capacitor C1 of the first switching tube Q1, the junction capacitor C2 of the second switching tube Q2, the first capacitor Cr, the excitation inductor Lm and the primary winding Np resonate, and the negative excitation current i_LmThe energy of a junction capacitor C1 of a first switch tube Q1 is extracted, the drain-source voltage Vds _ Q1 of the first switch tube Q1 drops, and meanwhile, a junction capacitor C2 of a second switch tube Q2 is charged, and the drain-source voltage of a second switch tube Q2 is chargedThe voltage Vds _ Q1 rises. At the same time, the voltage Vaux across the auxiliary winding Na also drops linearly.

At time t6, the voltage Vaux on the auxiliary winding Na drops to zero, which is determined to be the zero-crossing detection time (ZCD). Meanwhile, the timing circuit in the asymmetric half-bridge flyback converter starts to time from the moment.

At the time t7, the timing duration of the timing circuit reaches the duration corresponding to the preset third time Td and stops timing. At this time, the junction capacitor voltage of the second switch Q2 reaches the highest, the junction capacitor voltage of the first switch Q1 is pumped to zero voltage, and the second drive signal Vgs _ Q1 becomes high level, achieving zero voltage turn-on of the first switch Q1. This completes a cycle and then continues to repeat the operation according to the same operation.

Based on the above description of fig. 3 and 5, it can be seen that, during the period that the first switching tube Q1 is turned on, the absolute value Vaux1 | - (Na/Np) | (Vin-N × Vo) |, of the first sampling signal obtained after the sampling and holding; during the period that the second switch Q2 is turned on, the absolute value Vaux2 of the sampled second sampling signal is (Na/Np) × N × Vo. Na is the number of turns of the auxiliary winding, Np is the number of turns of the primary winding, Vin is input voltage, N is the turn ratio of the primary winding to the secondary winding, and Vo is output voltage.

In other embodiments, the first predetermined parameter and the second predetermined parameter of the asymmetric half-bridge flyback converter are both currents flowing through the voltage detection pin Vs of the controller 100 of the asymmetric half-bridge flyback converter, and the scheme may be applied to a controller chip where some pins do not support negative voltage. Specifically, the first predetermined parameter is the current flowing into the voltage detection pin Vs of the controller 100 during the conduction period of the first switch Q1, and the second predetermined parameter is the current flowing out of the voltage detection pin Vs of the controller 100 during the first conduction period of the second switch Q2. At this time, the comparison result of the comparison unit in the first control unit 110 on the first sampling signal and the second sampling signal is the comparison operation result on the absolute value of the first sampling signal and the absolute value of the second sampling signal. Further, referring to fig. 4, the asymmetric half-bridge flyback converter further includes: a third resistor RFB1, a third switching tube Q3, and a third control unit 140. The third resistor RFB1 is connected between the voltage detection pin Vs of the controller 100 and the different-name terminal of the auxiliary winding Na, and the same-name terminal of the auxiliary winding Na is connected to the reference ground; the third switching tube Q3 is connected between the voltage detection pin Vs of the controller 100 and the reference ground; and the third control unit 140 is connected to the control terminal of the third switch Q3 for controlling the conduction of the third switch Q3 during the conduction period of the first switch Q1 and the second switch Q2.

Optionally, in this embodiment, the third switching tube Q3 may be integrated inside the controller 100, or may be disposed outside the controller 100, which is not limited in the present invention. And in one possible embodiment, the third switching transistor Q3 is an NMOS field effect transistor.

In this embodiment, the operation principle of the asymmetric half-bridge flyback converter in one switching cycle in the DCM mode is substantially the same as that described in the foregoing embodiment with reference to fig. 5, and therefore, the description thereof is omitted. The differences are only that: in the present embodiment, the sampling and holding unit performs sampling and holding during the on period of the first switch Q1, and the sampling unit performs sampling during the on period of the second switch Q2, which are both the current Is flowing through the voltage detection pin Vs of the controller 100. Meanwhile, at the time when the first switching transistor Q1 is turned on and the time when the second switching transistor Q2 is turned on, the third control unit 140 outputs a high-level third driving signal Vgs _ Q3 to the gate of the third switching transistor Q3 to control the third switching transistor Q3 to be turned on.

Further, in this embodiment, after the comparison by the comparison unit, if the absolute value (denoted as Is1) of the first sampling signal Is greater than the product of the absolute value (denoted as Is2) of the second sampling signal and k2, that Is, Is1> k2 × Is2, the comparison unit triggers the first control unit 110 to control the second switch Q2 to be turned on twice in the current switching period; if the first sampling signal Is1 Is smaller than or equal to the product of the second sampling signal Is2 and k2, i.e., Is1 Is2 Is2, the comparing unit triggers the first control unit 110 to control the second switch Q2 to be turned on only once in the current switching period. Wherein the value range of k2 is 0.5 to 5, and preferably, the value range of k2 is 0.8 to 2.

Further, as can be seen from FIG. 4, theIn one embodiment, the first sampling signal obtained after the sample and hold is performed during the period that the first switch transistor Q1 is turned on

A second sampling signal obtained after sampling during the conduction period of the second switch tube Q2

Na is the number of turns of the auxiliary winding, Np is the number of turns of the primary winding, Vin is the input voltage, N is the turns ratio of the primary winding to the secondary winding, Vo is the output voltage, and RFB1 is the resistance of the third resistor.

In still other embodiments, the first predetermined parameter of the asymmetric half-bridge flyback converter is the on-time of the first switch Q1, and the second predetermined parameter of the asymmetric half-bridge flyback converter is the first on-time of the second switch Q2.

In this embodiment, the operation principle of the asymmetric half-bridge flyback converter in one switching cycle in the DCM mode is substantially the same as that described in the foregoing embodiment with reference to fig. 5, and therefore, the description thereof is omitted. The differences are only that: in this embodiment, the sampling and holding unit performs sampling and holding during the on period of the first switch Q1 to obtain the on time of the first switch Q1, and the sampling unit performs sampling during the on period of the second switch Q2 to obtain the on time of the second switch Q2. For example, in this embodiment, the sample-and-hold unit and the sampling unit may be configured as a timer or a counter to start timing when the first switch Q1 is turned on and the second switch Q2 is turned on for the first time, and stop timing when the first switch Q1 is turned off and the second switch Q2 is turned off for the first time, respectively.

Further, in this embodiment, after the comparison by the comparison unit, if the first sampling signal (denoted as Ton _ Q1) is smaller than the product of the second sampling signal (denoted as Ton _ Q2) and k3, that is, Ton _ Q1< k3 × Ton _ Q2, the comparison unit triggers the first control unit 110 to control the second switching tube Q2 to conduct twice in the current switching period; if the first sampling signal Ton _ Q1 is greater than or equal to the product of the second sampling signal Ton _ Q2 and k3, i.e., Ton _ Q1 ≧ k3 × Ton _ Q2, the comparing unit triggers the first control unit 110 to control the second switch Q2 to be turned on only once in the current switching period. Wherein the value range of k3 is 0.5 to 5, and preferably, the value range of k3 is 0.8 to 2.

It should be noted that, in each of the foregoing embodiments, the sample-and-hold unit and the sampling unit are respectively used to sample the first sampling signal and the second sampling signal. However, in the present disclosure, it is also possible to use only one sampling unit in the first control unit 110, and configure the sampling unit to sample the first predetermined parameter during the on period of the first switch Q1, transmit the sampling result to the register or buffer for buffering after the first switch Q1 is turned off, sample the second predetermined parameter by the sampling unit during the first on period of the second switch Q2, and then only need to simultaneously transmit the buffered signal and the signal sampled during the first on period of the second switch Q2 to the comparison unit for comparison. Therefore, resources can be saved, and the production cost can be reduced.

According to the method and the device, a certain judgment condition is set for the asymmetric half-bridge flyback conversion in the DCM mode, the deterioration influence of additionally turning on a second switching tube for one time in the application with a light load, low input voltage and high output voltage on the system efficiency can be avoided, and the asymmetric half-bridge flyback converter can have better working efficiency when realizing zero-voltage turning on under different application conditions.

Further, in the present disclosure, the second control unit 120 is configured to provide a driving signal Vgs _ Q1 that controls the first switching tube Q1 to be turned on and/or off. For example, the second control unit 120 is configured to sample the voltage Vaux across the auxiliary winding Na in each switching period, and generate a turn-on signal to control the turn-on of the first switching tube Q1, i.e., the driving signal Vgs _ Q1 in a high-level state, after delaying the voltage Vaux across the auxiliary winding Na by a third time Td from a high-to-low zero-crossing time. Wherein the third time Td is equal to the resonant cycle time of the asymmetric half-bridge flyback converter multiplied by x, wherein x includes but is not limited to one of 1/5, 9/40, 1/4, 7/24, 1/3, and x may be any real value in the range of 1/5 to 1/3, preferably 1/4.

The controller 100 further comprises an adaptive adjustment unit 130. The adaptive adjustment unit 130 is configured to adaptively adjust the magnitude of the first time according to the turn-on condition of the second switching tube Q2 in a next switching period of a specific switching period of the asymmetric half-bridge flyback converter. The second switch Q2 is turned on twice in each specific switching period.

For example, based on the foregoing detection method, if it is determined that the second switching transistor Q2 needs to be controlled to be turned on twice in some specific switching cycles (e.g. the 10 th switching cycle and the 13 th switching cycle) after the asymmetric half-bridge flyback converter is turned on, and the second switch Q2 is controlled to be turned on only once in the 11 th and 12 th switching periods, after the second switch Q2 is controlled to be turned on twice in the 10 th switching period, the adaptive adjustment unit 130 will determine whether the first switch Q1 is turned on (i.e. turned on at zero voltage) in the next switching period of the 10 th switching period, i.e. the 11 th switching period, when detecting that the first switching transistor Q1 is turned on hard in the 11 th switching period, the adaptive adjustment unit may generate a first adjustment signal to increase the second on-time of the second switching transistor Q2 by a second step duration in the 13 th switching period (i.e., to increase the first time by the second step duration); when detecting that the first switching transistor Q1 is turned on at zero voltage in the 11 th switching period, the adaptive adjustment unit may generate a second adjustment signal to decrease the second on-time of the second switching transistor Q2 by a first further period in the 13 th switching period (i.e., decrease the first time by the first further period). Therefore, the self-adaptive adjustment of the zero voltage switching of the first switching tube Q1 can be realized, so that the zero voltage switching of the asymmetric half-bridge flyback converter is closer to an ideal state. The method for determining whether the first switch Q1 is turned on at zero voltage in a certain switching period and the required circuit structure of the adaptive adjustment unit 130 can be understood with reference to the prior art, and will not be described in detail here.

Optionally, the first step duration and the second step duration may be the same or different, and the present invention is not limited thereto.

Further, in the present disclosure, the controller 100 may be configured to determine the mode of the asymmetric half-bridge flyback converter according to the size of the load of the asymmetric half-bridge flyback converter, for example, when the controller 100 detects that the load is greater than or equal to the first threshold, it may be determined that the asymmetric half-bridge flyback converter at this time operates in the BCM mode (critical mode); when the load is detected to be smaller than or equal to the second threshold, the asymmetric half-bridge flyback converter can be judged to work in a DCM mode; when the load is detected to be larger than the second threshold and smaller than the first threshold, it can be determined that the asymmetric half-bridge flyback converter is operated in the BUR mode at the moment. The BUR mode is a hiccup mode added between the BCM mode and the DCM mode, in order to reduce the influence on the system efficiency when the second switch Q2 needs to be turned on for the second time (since the second switch Q2 is also turned on hard, the system efficiency is affected). Of course, in other embodiments of the disclosure, the controller 100 may also be configured to determine the mode of the asymmetric half-bridge flyback converter by using other determination methods, which is not described herein again.

Specifically, in the BCM mode, the first control unit 110 may be configured to control the second switching tube Q2 to turn off after delaying for a second time; in the DCM mode, the first control unit 110 may be configured to control the second switch Q2 according to the methods described in the foregoing embodiments, which are not described herein again. In the BUR mode, the first control unit 110 may be configured to cycle through N switching cycles (each N switching cycle includes N-1 BCM cycles and 1 DCM cycle) as a BUR cycle, wherein the second switching tube Q2 is controlled to turn off after delaying for a second time in the first N-1 switching cycles of each N switching cycles, and the second switching tube Q2 is controlled in the nth switching cycle of each N switching cycles according to the methods described in the foregoing embodiments. In this way, the number of times of second turn-on of the second switching tube Q2 occurring in every N switching cycles is reduced, so that the purpose of optimizing the system efficiency can be achieved. Wherein N is an integer greater than 1.

Referring to fig. 6, fig. 6 is a flowchart illustrating a control method of an asymmetric half-bridge flyback converter according to an embodiment of the present disclosure, which may be used in the asymmetric half-bridge flyback converters described in fig. 3 to 5.

As shown in fig. 6, in the present disclosure, the method of controlling the flyback converter includes performing steps S01 to S05.

Specifically, in step S01, a first predetermined parameter of the asymmetric half-bridge flyback converter is sampled during the period that the first switching tube is turned on, so as to obtain a first sampling signal.

In step S02, a second predetermined parameter of the asymmetric half-bridge flyback converter is sampled during the first turn-on period of the second switching tube, so as to obtain a second sampling signal.

In some embodiments, the first predetermined parameter and the second predetermined parameter are both the voltage across any winding of the transformer TR, preferably across the auxiliary winding Na. At this time, the comparison result of the comparison unit in the first control unit 110 on the first sampling signal and the second sampling signal is the comparison operation result on the absolute value of the first sampling signal and the absolute value of the second sampling signal. For example, the predetermined parameter is taken as the voltage across the auxiliary winding Na, and the sampling of the first predetermined parameter of the asymmetric half-bridge flyback converter during the conduction period of the first switch tube is to perform sampling and holding on the voltage across the auxiliary winding Na by using the sample-and-hold unit in the first control unit 100 during the conduction period of the first switch tube Q1 (for example, during the time period from t0 to t1 in fig. 5). And, sampling a second predetermined parameter of the asymmetric half-bridge flyback converter during the first turn-on period of the second switching tube, that is, sampling the voltage across the auxiliary winding Na by using the sampling unit in the first control unit 100 during the first turn-on period of the second switching tube Q2 (for example, during the time period t2-t3 in fig. 5).

In other embodiments, the first predetermined parameter and the second predetermined parameter are both currents flowing through the voltage sense pin Vs of the controller 100 of the asymmetric half-bridge flyback converter. At this time, the comparison result of the comparison unit in the first control unit 110 on the first sampling signal and the second sampling signal is the comparison operation result on the absolute value of the first sampling signal and the absolute value of the second sampling signal. Furthermore, sampling the first predetermined parameter of the asymmetric half-bridge flyback converter during the turn-on period of the first switching tube is to sample and hold the current flowing into the voltage detection pin Vs of the controller 100 by using the sample and hold unit in the first control unit 100 during the turn-on period of the first switching tube Q1 (e.g., during the time period t0-t1 in fig. 5). And, sampling the second predetermined parameter of the asymmetric half-bridge flyback converter during the first turn-on period of the second switching tube, that is, sampling the current flowing out of the voltage detection pin Vs of the controller 100 by using the sampling unit in the first control unit 100 during the first turn-on period of the second switching tube Q2 (for example, during the time period t2-t3 in fig. 5).

In still other embodiments, the first predetermined parameter is the on-time of the first switch Q1, and the sampling of the first predetermined parameter of the asymmetric half-bridge flyback converter during the on-time of the first switch Q1 is to start the timing at the on-time of the first switch Q1 (e.g., at time t0 in fig. 5), stop the timing at the off-time of the first switch Q1 (e.g., at time t1 in fig. 5), and buffer the timing result.

The second predetermined parameter is the first on-time of the second switch Q2, and the sampling of the second predetermined parameter of the asymmetric half-bridge flyback converter during the first on-time of the second switch Q2 is to start the timing at the first on-time of the second switch Q2 (e.g., at time t2 in fig. 5) and stop the timing at the first off-time of the second switch Q1 (e.g., at time t3 in fig. 5).

In step S03, the magnitudes of the first and second sampled signals are compared. Wherein, the step S04 is executed if the comparison result satisfies the requirement, and the step S05 is executed if the comparison result does not satisfy the requirement.

In particular, when the first predetermined parameter and the second predetermined parameter are both the voltage across the auxiliary winding Na, the absolute value Vaux1 of the first sampled signal and the absolute value Vaux2 of the second sampled signal are compared by a comparison unit in the first control unit 110, and when the comparison result is that the absolute value Vaux1 of the first sampled signal is greater than the product of the absolute value Vaux2 of the second sampled signal and k1, or if the difference between the absolute value Vaux1 of the first sampling signal and the absolute value Vaux2 of the second sampling signal is greater than a, trigger the step S04, and when the comparison result is that the absolute value Vaux1 of the first sampled signal is less than or equal to the product of the absolute value Vaux2 of the second sampled signal and k1, or if the difference between the absolute value Vaux1 of the first sampling signal and the absolute value Vaux2 of the second sampling signal is less than or equal to a, triggering to execute step S05, where the value range of k1 is 0.5 to 5, and the value range of a is greater than zero.

When the first predetermined parameter and the second predetermined parameter are both currents flowing through the voltage detection pin Vs of the controller 100 of the asymmetric half-bridge flyback converter, the comparison unit in the first control unit 110 compares the absolute value Is1 of the first sampling signal with the absolute value Is2 of the second sampling signal, and triggers the execution of step S04 when the comparison result Is that the absolute value Is1 of the first sampling signal Is greater than the product of the absolute values Is2 and k2 of the second sampling signal, and triggers the execution of step S05 when the comparison result Is that the absolute value Is1 of the first sampling signal Is less than or equal to the product of the absolute values Is2 and k2 of the second sampling signal, wherein the value range of k2 Is 0.5 to 5, and preferably, the value range of k2 Is 0.8 to 2.

When the first predetermined parameter is the on-time of the first switch Q1 and the second predetermined parameter is the first on-time of the second switch Q2, the comparison unit in the first control unit 110 compares the magnitudes of the first sampling signal Ton _ Q1 and the second sampling signal Ton _ Q2, and triggers the execution of step S04 when the comparison result is that the first sampling signal Ton _ Q1 is smaller than the product of the second sampling signal Ton _ Q2 and k3, and triggers the execution of step S05 when the comparison result is that the first sampling signal Ton _ Q1 is greater than or equal to the product of the second sampling signal Ton _ Q2 and k3, wherein the value of k3 ranges from 0.5 to 5.

It is understood that k1, k2 and k3 may or may not be the same.

In step S04, the second switch tube is controlled to be additionally turned on for a first time.

After the second switch Q2 is turned off for the first time, the first driving signal Vgs _ Q2 with a high level may be provided to the gate of the second switch Q2 again after a certain time interval to control the second switch Q2 to conduct for the second time additionally, and the second conducting time may be set as the first time, so that the second switch Q2 is turned on twice in the current switching period. For a specific method, reference may be made to the foregoing description of fig. 5, which is not repeated herein.

Further, after step S04, the control method further includes: and judging whether the first switching tube is switched on at zero voltage in the next switching period, if so, reducing the first time by a first step time, otherwise, increasing the first time by a second step time. Specifically, reference may be made to the foregoing description of the adaptive adjustment unit 130, which is not described herein again.

In step S05, the second switch tube is controlled to conduct once in the current switching period.

After the second switching tube Q2 is turned off for the first time, triggering a timing circuit in the asymmetric half-bridge flyback converter to start timing at a zero-crossing detection time (ZCD) when the voltage Vaux on the auxiliary winding Na drops to zero, and triggering the second control unit 120 to output a second driving signal Vgs _ Q1 with a high level when the timing duration reaches a duration corresponding to a preset third time Td, so as to control the first switching tube Q1 to be turned on, so that the second switching tube Q2 is turned on only once in the current switching period.

Further, the present disclosure also provides another control method for an asymmetric half-bridge flyback converter, which can also be used in the asymmetric half-bridge flyback converters described in fig. 3 to 5. The control method comprises the following steps: sampling output voltage information of the asymmetric half-bridge flyback converter during the first conduction period of the second switching tube to obtain a first sampling signal; and comparing the first sampling signal with the voltage threshold, and controlling the second switching tube to be switched on again for the first time under the condition that the comparison result meets the requirement, otherwise, controlling the second switching tube to be switched on once in the current switching period.

In this embodiment, the manner of obtaining the first sampling signal includes: and sampling the voltage at two ends of any winding in the transformer during the first conduction period of the second switching tube to obtain the first sampling signal. The first sampling signal is in a proportional relation with the output voltage of the asymmetric half-bridge flyback converter, and represents the information of the output voltage.

Further, in this embodiment, the asymmetric half-bridge flyback converter operates in discontinuous mode. And specifically, when the first sampling signal is greater than the voltage threshold, controlling the second switching tube to be switched on again for the first time, otherwise, controlling the second switching tube to be switched on once in the current switching period. Here, the voltage threshold is set to a certain appropriate value, for example, when the fluctuation range of the output voltage is between 10 to 20V, the voltage threshold may be set to 16V, and thus, the efficiency may be maximally improved.

Further, the present disclosure also provides another control method of an asymmetric half-bridge flyback converter, which can also be used in the asymmetric half-bridge flyback converters described in the foregoing fig. 3 to 5. The control method comprises the following steps: judging the working mode of the asymmetric half-bridge flyback converter based on the load size of the asymmetric half-bridge flyback converter; under the condition that the working mode of the asymmetric half-bridge flyback converter is judged to be a critical mode, the second switching tube is controlled to be turned off after delaying for a second time; in the case that the working mode of the asymmetric half-bridge flyback converter is determined to be the discontinuous mode, controlling the second switching tube according to the control method as described in fig. 6; and under the condition that the working mode of the asymmetric half-bridge flyback converter is determined to be the hiccup mode, controlling the second switching tube to be turned off after delaying for a second time in the first N-1 switching cycles in each N switching cycles, and controlling the second switching tube according to the control method described in the figure 6 in the Nth switching cycle in each N switching cycle, wherein N is an integer greater than 1.

For example, the operation mode of the asymmetric half-bridge flyback converter may be determined as a critical mode when the load is greater than or equal to a first threshold, may be determined as a discontinuous mode when the load is less than or equal to a second threshold, and may be determined as a hiccup mode when the load is greater than the second threshold and less than the first threshold.

In summary, according to the technical scheme of the disclosure, it can be determined whether the asymmetric half-bridge flyback converter in the DCM mode needs to turn on the second switching tube twice in one switching period by setting a certain determination condition, so that the asymmetric half-bridge flyback converter has better working efficiency under different application conditions. Meanwhile, the problem of audio noise can be effectively improved.

On the other hand, the hiccup mode is arranged between the BCM mode (critical mode) and the DCM mode, so that the second-time switching-on times of the second switching tube occurring in every N switching periods can be reduced, and the system efficiency is further optimized.

Finally, it should be noted that: it should be understood that the above examples are only for clearly illustrating the present invention and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.

Claims

1. A control method of an asymmetric half-bridge flyback converter, the asymmetric half-bridge flyback converter comprises a first switch tube and a second switch tube which form a half bridge, a transformer and a controller, and in each switch period, the control method comprises the following steps:

and comparing the magnitude of the first sampling signal with that of the second sampling signal, and controlling the second switching tube to be switched on again for the first time under the condition that the comparison result meets the requirement, otherwise, controlling the second switching tube to be switched on once in the current switching period.

2. The control method of claim 1 wherein the asymmetric half-bridge flyback converter operates in discontinuous mode.

3. The control method of claim 1, wherein the transformer includes a primary winding, a secondary winding, and an auxiliary winding, the first predetermined parameter and the second predetermined parameter are each a voltage across any one of the windings of the transformer,

the comparison result is a comparison operation result of the absolute value of the first sampling signal and the absolute value of the second sampling signal.

4. The control method according to claim 3, wherein a requirement is satisfied when the comparison result is that the absolute value of the first sampled signal is larger than the product of the absolute value of the second sampled signal and k1,

wherein the value range of k1 is 0.5-5.

5. The control method according to claim 3, wherein a requirement is satisfied when the comparison result is that the difference between the absolute value of the first sampled signal and the absolute value of the second sampled signal is greater than a,

wherein the value range of a is larger than zero.

6. A control method according to claim 3, wherein the first and second predetermined parameters are both the voltage across the auxiliary winding.

7. The control method according to claim 1, wherein the first predetermined parameter and the second predetermined parameter are both currents flowing through a voltage detection pin of a controller of the asymmetric half-bridge flyback converter, the comparison result is a comparison operation result of an absolute value of the first sampling signal and an absolute value of the second sampling signal,

8. The control method according to claim 7, wherein a requirement is satisfied when the comparison result is that the absolute value of the first sampled signal is greater than the product of the absolute value of the second sampled signal and k2,

wherein the value range of k2 is 0.5-5.

9. The control method according to claim 1, wherein the first predetermined parameter is the conduction time of the first switch tube, the second predetermined parameter is the first conduction time of the second switch tube, and the comparison result is that the first sampling signal is smaller than the product of the second sampling signal and k3,

wherein the value range of k3 is 0.5-5.

10. The control method of claim 1, wherein after controlling the second switching tube to be additionally turned on for a first time, the control method further comprises:

11. A control method of an asymmetric half-bridge flyback converter, the asymmetric half-bridge flyback converter comprises a first switching tube and a second switching tube which form a half bridge, a transformer and a controller, and the control method comprises the following steps:

12. The control method according to claim 11, wherein when the first sampling signal is greater than the voltage threshold, the second switching tube is turned on again for a first time, and otherwise, the second switching tube is controlled to be turned on once in a current switching period.

13. The control method of claim 11, wherein the asymmetric half-bridge flyback converter operates in discontinuous mode.

14. The control method according to claim 11, wherein the transformer comprises a primary winding, a secondary winding and an auxiliary winding, and the first sampling signal is obtained by sampling a voltage across any one of the windings in the transformer.

15. An asymmetric half-bridge flyback converter, wherein the asymmetric half-bridge flyback converter comprises:

the excitation inductor is connected between the common connection point of the first switching tube and the second switching tube and the transformer;

a first capacitor connected between a reference ground and the primary winding; and

wherein the controller includes:

the first control unit is configured to sample a first preset parameter of the asymmetric half-bridge flyback converter during the conduction period of the first switching tube and sample a second preset parameter of the asymmetric half-bridge flyback converter during the first conduction period of the second switching tube, and the first control unit is further configured to compare the two sampling results and control the conduction times of the second switching tube in one switching period according to the comparison result;

16. The asymmetric half-bridge flyback converter of claim 15, wherein the first predetermined parameter and the second predetermined parameter are both voltages across any winding in the transformer.

17. The asymmetric half-bridge flyback converter of claim 16, wherein the first predetermined parameter and the second predetermined parameter are both voltages across the auxiliary winding, and further comprising:

18. The asymmetric half-bridge flyback converter of claim 15, wherein the first predetermined parameter and the second predetermined parameter are each a current flowing through a voltage sense pin of a controller of the asymmetric half-bridge flyback converter, and further comprising:

19. The asymmetric half-bridge flyback converter of claim 15, wherein the first predetermined parameter is a turn-on time of the first switching tube and the second predetermined parameter is a first turn-on time of the second switching tube.

20. An asymmetric half-bridge flyback converter according to any of claims 15-19, wherein the first control unit further comprises:

21. The asymmetric half-bridge flyback converter of claim 20, wherein the controller further comprises:

the self-adaptive adjusting unit is configured to self-adaptively adjust the size of the first time according to whether the second switch tube is in a zero-voltage switching condition in the next switching period of the asymmetric half-bridge flyback converter.