A method for controlling mode switching of a power converter

Abstract

The present invention discloses a method for controlling the mode switching of a power converter, which relates to the field of integrated circuits. The method for controlling the mode switching of the power converter includes the following steps: Step 1: The power converter is powered on and starts to output; Step 2: When the resonance number of the AC waveform is less than 1, the working mode of the power converter is CCM mode power supply; Step 3: When the resonance number of the AC waveform is greater than or equal to 1 and less than or equal to 4, the working module of the power converter is QR mode; Step 4: When the resonance number of the AC waveform is greater than 4, the working module of the power converter is DCM mode; The method for controlling the mode switching of the power converter further includes a control device. Compared with the prior art, the beneficial effects of the present invention are: The present invention controls the conduction state of the power tube according to different waveform resonance numbers, realizes the seamless switching of the CCM, QR, and DCM working modes of the power converter, and improves the conversion efficiency, EMI and other indicators of the power converter.

Description

Technical Field

[0001] The present invention relates to the field of integrated circuits, and specifically to a method for controlling the mode switching of a power converter. Background Art

[0002] Conversion efficiency is a very important indicator of a power converter. The conversion efficiency is related to parameters such as the switching frequency, the on-resistance of the power transistor, and the parasitic capacitance of the power transistor. For the control chip of the power converter, it is necessary to optimize the system operating frequency, the on-time of the power transistor, the operating mode, etc. under different load conditions to maximize the average efficiency of the power converter.

[0003] Currently, most power converters on the market adopt the discontinuous conduction mode (DCM) as the operating mode. This control mode is simple to operate and the system has good stability. The disadvantages are that the operating frequency is relatively low and the efficiency is relatively low; the quasi-resonant (QR) operating mode has an improvement in frequency and efficiency compared to the discontinuous conduction mode. However, since the power transistor is turned on near the resonant valley, the spectrum is relatively concentrated and the EMI is relatively poor; the continuous conduction mode (CCM) has a relatively high operating frequency, but there are easy system stability problems.

[0004] The above several operating modes are combined into a new control strategy for the power converter. However, due to the advantages and disadvantages of each operating mode itself, it is necessary to optimize the relevant key parameters in the circuit design to meet the increasing demands of users; for example, users will test indicators such as the EMI and conversion efficiency of the power converter at each load point. These indicators are related to the operating mode, operating frequency, etc., and often conflict with each other. Therefore, it is necessary to optimize the method for controlling the mode switching to improve indicators such as the conversion efficiency and EMI. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for controlling the mode switching of a power converter to solve the problems raised in the above background art.

[0006] To achieve the above purpose, the present invention provides the following technical solution:

[0007] A method for controlling the mode switching of a power converter includes the following steps:

[0008] Step 1: The power converter is powered on and starts to output.

[0009] Step 2: When the resonance number of the alternating current waveform is less than 1, the operating mode of the power converter is the CCM mode for power supply.

[0010] Step 3: When the resonance number of the alternating current waveform is greater than or equal to 1 and less than or equal to 4, the operating mode of the power converter is the QR mode.

[0011] Step 4: When the resonance number of the alternating current waveform is greater than 4, the operating mode of the power converter is the DCM mode.

[0012] The power converter mode switching control method further includes a control device, and the control device includes:

[0013] A power conversion control unit 100, configured to select different mode outputs according to the number of resonances and control the power transistor 140 to conduct;

[0014] The power transistor 140, configured to conduct to ground so that current flows into the input side of the transformer 110;

[0015] A sampling resistor 141, configured to sample the current flowing through the power transistor 140 and output it to the power conversion control unit 100;

[0016] The transformer 110, configured to supply power to the output feedback circuit 120 and the output rectification and filtering circuit 130 through the output side;

[0017] The output feedback circuit 120, configured to feedback the number of resonances on the output side of the transformer 110 to the power conversion control unit 100;

[0018] The output rectification and filtering circuit 130, configured to convert the alternating current input by the transformer 110 into direct current for output;

[0019] The output end of the power conversion control unit 100 is connected to the G pole of the power transistor 140, the D pole of the power transistor 140 is connected to one end of the input side of the transformer 110, the S pole of the power transistor 140 is connected to the sampling resistor 141 and the first input end of the power conversion control unit 100, the other end of the sampling resistor 141 is grounded, the other end of the input side of the transformer 110 is connected to the input voltage, the output side of the transformer 110 is connected to the input end of the output feedback circuit 120 and the input end of the output rectification and filtering circuit 130, and the output end of the feedback circuit 120 is connected to the second input end of the power conversion control unit 100.

[0020] As a further solution of the present invention: in step 1: the power conversion control unit 100 is powered on to output a voltage to the G pole of the power transistor 140, and then stores energy through the excitation of the transformer 110; when the power transistor 140 is turned off, the transformer 110 demagnetizes and transfers energy to the output feedback circuit 120 and the output rectification and filtering circuit 130; after the demagnetization energy transfer of the transformer 110 is completed, the excitation inductor of the transformer 110 and the junction capacitance LC of the power transistor 140 resonate to generate alternating current on the input side of the transformer 110, and the alternating current is input to the D pole of the power transistor 140 again, and so on.

[0021] As a further solution of the present invention: In step 2: When the resonance number of the AC waveform on the output side of the transformer 110 is less than 1, that is, the resonance number of the waveform of the feedback signal FB of the feedback circuit 120 is less than 1, the feedback signal FB is output to the power conversion control unit 100. The power conversion control unit 100 controls the voltage level of the G pole of the power transistor 140 according to the feedback signal FB. The transformer 110 reciprocally magnetizes to store energy and demagnetizes to output energy, and the system operates in the CCM mode.

[0022] As a further solution of the present invention: In step 3: When the resonance number of the AC waveform on the output side of the transformer 110 is greater than or equal to 1 and less than or equal to 4, that is, the resonance number of the waveform of the feedback signal FB of the feedback circuit 120 is greater than or equal to 1 and less than or equal to 4, the feedback signal FB is output to the power conversion control unit 100. The power conversion control unit 100 controls the voltage level of the G pole of the power transistor 140 according to the feedback signal FB. The transformer 110 reciprocally magnetizes to store energy and demagnetizes to output energy, and the system operates in the QR mode.

[0023] As a further solution of the present invention: In step 4: When the resonance number of the AC waveform on the output side of the transformer 110 is greater than 4, that is, the resonance number of the waveform of the feedback signal FB of the feedback circuit 120 is greater than 4, the feedback signal FB is output to the power conversion control unit 100. The power conversion control unit 100 controls the voltage level of the G pole of the power transistor 140 according to the feedback signal FB. The transformer 110 reciprocally magnetizes to store energy and demagnetizes to output energy, and the system operates in the DCM mode.

[0024] As a further solution of the present invention: The feedback circuit 120 includes a resistor R1 and a resistor R2. One end of the resistor R1 is connected to one side of the output side of the transformer 110, the other end of the resistor R1 is connected to the resistor R2 and the second input end of the power conversion control unit 100, the other end of the resistor R2 is grounded, and the other side of the output side of the transformer 110 is grounded.

[0025] As a further solution of the present invention: The power conversion control unit 100 includes a power transistor conduction trigger circuit 150, a comparator 151, a shaping circuit 152, a combinational logic circuit 153, a power transistor turn-off trigger circuit 154, a flip-flop 155, and a power transistor drive circuit 156. The output terminal of the power transistor conduction trigger circuit 150 is connected to the input terminal of the combinational logic circuit 153. The output terminal of the comparator 151 is connected to the input terminal of the shaping circuit 152. The output terminal of the shaping circuit 152 is connected to the input terminal of the combinational logic circuit 153. The output terminal of the combinational logic circuit 153 is connected to the input terminal of the flip-flop 155. The output terminal of the power transistor turn-off trigger circuit 154 is connected to the input terminal of the flip-flop 155. The output terminal of the flip-flop 155 is connected to the input terminal of the power transistor drive circuit 156. The input terminal of the power transistor conduction trigger circuit 150 is connected to the non-inverting input terminal of the comparator 151 and the output terminal of the feedback circuit 120. The inverting input terminal of the comparator 151 is connected to the reference voltage source V01. The input terminal of the power transistor turn-off trigger circuit 154 is connected to the S pole of the power transistor 140. The output terminal of the power transistor drive circuit 156 is connected to the G pole of the power transistor 140.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention controls the conduction state of the power transistor according to different waveform resonance numbers, realizes seamless switching of the CCM, QR, and DCM working modes of the power converter, and improves the conversion efficiency, EMI and other indicators of the power converter. Description of the Drawings

[0027] Figure 1 It is a system schematic diagram of a power converter mode switching control method.

[0028] Figure 2 It is a mode switching block diagram of a power converter mode switching control method.

[0029] Figure 3 It is a mode switching waveform diagram of a power converter mode switching control method.

[0030] Figure 4 It is an internal circuit diagram of the power conversion control unit.

[0031] In the figure: Power conversion control unit - 100, Transformer - 110, Output feedback circuit - 120, Output rectification and filtering circuit - 130, Power transistor - 140, Sampling resistor - 141, Trigger circuit 150, Comparator 151, Shaping circuit 152, Combinational logic circuit 153, Power transistor turn-off trigger circuit 154, Flip-flop 155, Power transistor drive circuit 156. Detailed Embodiment

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] Please refer to Figure 1 , a power converter mode switching control method, comprising the following steps:

[0034] Step 1: The power converter is powered on and starts to output.

[0035] Step 2: When the resonance number of the AC waveform is less than 1, the power converter operates in the CCM mode to supply power.

[0036] Step 3: When the resonance number of the AC waveform is greater than or equal to 1 and less than or equal to 4, the power converter operating module is in the QR mode.

[0037] Step 4: When the resonance number of the AC waveform is greater than 4, the power converter operating module is in the DCM mode.

[0038] The power converter mode switching control method further includes a control device, and the control device includes:

[0039] A power conversion control unit 100, configured to select different mode outputs according to the resonance number and control the power transistor 140 to conduct.

[0040] The power transistor 140 is used to conduct to ground, so that current flows into the input side of the transformer 110.

[0041] The sampling resistor 141 is used to sample the current flowing through the power transistor 140 and output it to the power conversion control unit 100.

[0042] The transformer 110 is used to supply power to the output feedback circuit 120 and the output rectification and filtering circuit 130 through the output side.

[0043] The output feedback circuit 120 is used to feedback the resonance number of the output side of the transformer 110 to the power conversion control unit 100.

[0044] The output rectification and filtering circuit 130 is used to convert the alternating current input by the transformer 110 into direct current for output.

[0045] The output terminal of the power conversion control unit 100 is connected to the G pole of the power transistor 140. The D pole of the power transistor 140 is connected to one end of the input side of the transformer 110. The S pole of the power transistor 140 is connected to the sampling resistor 141 and the first input terminal of the power conversion control unit 100. The other end of the sampling resistor 141 is grounded. The other end of the input side of the transformer 110 is connected to the input voltage. The output side of the transformer 110 is connected to the input terminal of the output feedback circuit 120 and the input terminal of the output rectification and filtering circuit 130. The output terminal of the feedback circuit 120 is connected to the second input terminal of the power conversion control unit 100.

[0046] In this embodiment: Please refer to Figures 1 to 3 , in step 1: The power conversion control unit 100 is powered on to output a voltage to the G pole of the power transistor 140, and then stores energy through the excitation of the transformer 110. When the power transistor 140 is turned off, the transformer 110 demagnetizes and transfers energy to the output feedback circuit 120 and the output rectification and filtering circuit 130. After the demagnetization energy transfer of the transformer 110 is completed, the excitation inductor of the transformer 110 and the junction capacitance LC of the power transistor 140 resonate to generate an alternating current on the input side of the transformer 110, and the alternating current is input to the D pole of the power transistor 140 again, and so on.

[0047] The power transistor 140 can be an NMOS transistor, whose D pole and S pole are used as the current input terminal and the current output terminal respectively, and whose G pole is used as the switch control terminal;

[0048] The output rectification and filtering circuit 130 includes a rectifier diode, a filter capacitor, and an output resistor. The rectifier diode converts the alternating current into direct current, and the filter capacitor and the output resistor are used to filter the generated direct current. The input voltage VIN is input to the input side of the transformer 110.

[0049] In this embodiment: Please refer to Figures 1 to 3 , in step 2: When the resonance number of the alternating current waveform on the output side of the transformer 110 is less than 1 (such as 0), that is, the resonance number of the waveform of the feedback signal FB of the feedback circuit 120 is less than 1, the feedback signal FB is output to the power conversion control unit 100. The power conversion control unit 100 controls the voltage level of the G pole of the power transistor 140 according to the feedback signal FB. The transformer 110 reciprocally stores energy through excitation and outputs energy through demagnetization, and the system operates in the CCM mode.

[0050] The feedback signal FB is connected to the power conversion control unit 100, mainly generating two control signals. One is the enable signal ON_en for turning on the power transistor 140; the other is the generation of the valley signal V (n) ; The power conversion control unit 100 generates a control signal ModeControl signal through the valley signal V (n) ; The ModeControl signal is at the first valley V (1)((Waveform resonance number is 1) and the fourth valley V (4) is high level between (waveform resonance number is 4), and other states are low level; when the waveform resonance number is less than 1, the ModeControl signal is low level and ineffective, and the enable signal ON_en controls the G pole of the power transistor 140 to be high level, thereby controlling the output and completing the CCM mode output.)

[0051] In this embodiment: Please refer to Figures 1 to 3 , in step 3: when the waveform resonance number of the alternating current on the output side of the transformer 110 is greater than or equal to 1 and less than or equal to 4, that is, when the waveform resonance number of the feedback signal FB of the feedback circuit 120 is greater than or equal to 1 and less than or equal to 4, the feedback signal FB is output to the power conversion control unit 100. The power conversion control unit 100 controls the G pole voltage of the power transistor 140 according to the feedback signal FB. The transformer 110 reciprocally magnetizes to store energy and demagnetizes to output energy, and the system operates in the QR mode.)

[0052] When the resonance number is zero, the ModeControl signal is low level (the first paragraph). It can be seen from the combinational logic circuit 153 in Figure 2 that when the ON_en signal is high level, the ON signal is high level, and the power transistor 140 is immediately turned on, which is the CCM mode; when the resonance number is between 1 and 4, the ModeControl signal is high level (the second paragraph). Only when both the ON_en and 164 signals are high level, the ON signal is high level. At this time, the high level of 164 corresponds to the low level of 162, which corresponds to the valley of the FB signal. This stage is defined as the QR mode; in the third paragraph, the ModeControl signal is low level, and the control result is the same as that of the first paragraph, but the ON_en is no longer the straight-line output in the CCM mode, but multiple resonance outputs, and the mode is defined as the DCM mode. Please refer to the waveform diagrams of the CCM mode and the DCM mode in Figure 3 .)

[0053] In this embodiment: Please refer to Figures 1 to 3 , in step 4: when the waveform resonance number of the alternating current on the output side of the transformer 110 is greater than 4, that is, when the waveform resonance number of the feedback signal FB of the feedback circuit 120 is greater than 4, the feedback signal FB is output to the power conversion control unit 100. The power conversion control unit 100 controls the G pole voltage of the power transistor 140 according to the feedback signal FB. The transformer 110 reciprocally magnetizes to store energy and demagnetizes to output energy, and the system operates in the DCM mode.)

[0054] When the waveform resonance number is greater than 4, the ModeControl signal is at a low level and ineffective. At this time, according to the number of resonance waves of the feedback signal FB, the output frequency of the enable signal ON_en corresponds to the number of resonance waves, so as to control the conduction state of the power transistor 140 (the D pole of the power transistor 140 inputs current, and the S pole is grounded through a sampling resistor), and then control the AC frequency on the input side of the transformer 110, change the AC frequency on the output side, and the system operates in the DCM mode.

[0055] Figure 3 In [the circuit], during the conduction stage of the power transistor 140, the control circuit superimposes a periodic time deviation amount Δton on the power transistor conduction time Ton to improve the system EMI performance;

[0056] In this embodiment: Please refer to Figure 1 , the feedback circuit 120 includes a resistor R1 and a resistor R2. One end of the resistor R1 is connected to one side of the output side of the transformer 110, the other end of the resistor R1 is connected to the resistor R2 and the second input end of the power conversion control unit 100, the other end of the resistor R2 is grounded, and the other side of the output side of the transformer 110 is grounded.

[0057] The AC on the output side of the transformer 110 is grounded through the series resistors R1 and R2, and the AC (number of voltage harmonics) at the connection point of the resistors R1 and R2 is collected, and the feedback signal FB is output to the power conversion control unit 100.

[0058] In this embodiment: Please refer to Figure 4 , the power conversion control unit 100 includes a power transistor conduction trigger circuit 150, a comparator 151, a shaping circuit 152, a combinational logic circuit 153, a power transistor turn-off trigger circuit 154, a flip-flop 155, and a power transistor drive circuit 156. The output end of the power transistor conduction trigger circuit 150 is connected to the input end of the combinational logic circuit 153, the output end of the comparator 151 is connected to the input end of the shaping circuit 152, the output end of the shaping circuit 152 is connected to the input end of the combinational logic circuit 153, the output end of the combinational logic circuit 153 is connected to the input end of the flip-flop 155, the output end of the power transistor turn-off trigger circuit 154 is connected to the input end of the flip-flop 155, and the output end of the flip-flop 155 is connected to the input end of the power transistor drive circuit 156; the input end of the power transistor conduction trigger circuit 150 is connected to the non-inverting input end of the comparator 151 and the output end of the feedback circuit 120, the inverting input end of the comparator 151 is connected to the reference voltage source V01, the input end of the power transistor turn-off trigger circuit 154 is connected to the S pole of the power transistor 140, and the output end of the power transistor drive circuit 156 is connected to the G pole of the power transistor 140.

[0059] The turn-on trigger signal ON of the power transistor is generated by the FB signal, and the turn-off trigger signal OFF of the power transistor is generated by the CS signal. After the shown FB signal is compared with the reference voltage source V01 (0.1V) by the comparator 151, the 161 signal is output. This signal generates the 162 signal and the mode control ModeControl signal 163 after passing through the shaping circuit 152. The 164 signal is generated after the 162 signal is inverted. The ON signal set flip-flop 155 is generated after the logical combination of the 164 signal, the mode control signal ModeControl, and the output signal ON_en of the power transistor turn-on trigger circuit. The high level output by the flip-flop 155 conducts the power transistor 140 after passing through the level conversion of the drive circuit; after the power transistor 140 conducts, the current flowing through the power transistor continuously increases, and the voltage value of the CS signal also continuously increases after passing through the sampling resistor 141. When the CS signal reaches the set voltage threshold, the power transistor turn-off trigger circuit 154 outputs the OFF signal to reset the flip-flop 155, and the low level output by the flip-flop 155 turns off the power transistor 140 after passing through the level conversion of the drive circuit.

[0060] The mode control ModeControl signal 163 has three segments. The first low level indicates the CCM mode, the second high level indicates the QR mode, and the third low level indicates the DCM mode. The signal CS is used to feedback a signal to the power transistor turn-off trigger circuit 154 when the current on the input side of the transformer 110 is too large, and control the flip-flop 155 to stop outputting.

[0061] The working principle of the present invention is as follows: The power conversion control unit 100 selects different modes for output according to the resonance number, controls the power transistor 140 to conduct, and the power transistor 140 conducts to ground, so that current flows into the input side of the transformer 110. The sampling resistor 141 samples the current flowing through the power transistor 140 and outputs it to the power conversion control unit 100. The transformer 110 supplies power to the output feedback circuit 120 and the output rectifier and filter circuit 130 through the output side. The output feedback circuit 120 feeds back the resonance number of the output side of the transformer 110 to the power conversion control unit 100, and the output rectifier and filter circuit 130 converts the alternating current input by the transformer 110 into direct current for output; the output feedback circuit 120 outputs the feedback signal FB to the power conversion control unit 100, and the feedback signal FB carries the harmonic number of the output side of the transformer 110. The power conversion control unit 100 selects one of the CCM mode, QR mode, and DCM mode for output according to the harmonic number.

[0062] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

[0063] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A power converter mode switching control method, characterized in that this power converter mode switching control method is implemented by a control device, and the control device includes: a power conversion control unit (100) for selecting different mode outputs according to the resonance number of the AC waveform and controlling the conduction of the power transistor (140); the resonance number of the AC waveform refers to the valley count of the voltage oscillation waveform at the D pole of the power transistor during the demagnetization process of the transformer; a power transistor (140) for conducting to ground so that current flows into the input side of the transformer (110); a sampling resistor (141) for sampling the current flowing through the power transistor (140) and outputting it to the power conversion control unit (100); a transformer (110) for supplying power to the output feedback circuit (120) and the output rectifying and filtering circuit (130) through the output side; an output feedback circuit (120) for feeding back the resonance number of the AC waveform on the output side of the transformer (110) to the power conversion control unit (100); an output rectifying and filtering circuit (130) for converting the AC power input by the transformer (110) into DC power for output; the output end of the power conversion control unit (100) is connected to the G pole of the power transistor (140), the D pole of the power transistor (140) is connected to one end of the input side of the transformer (110), the S pole of the power transistor (140) is connected to the sampling resistor (141) and the first input end of the power conversion control unit (100), the other end of the sampling resistor (141) is grounded, the other end of the input side of the transformer (110) is connected to the input voltage, the output side of the transformer (110) is connected to the input end of the output feedback circuit (120) and the input end of the output rectifying and filtering circuit (130), and the output end of the output feedback circuit (120) is connected to the second input end of the power conversion control unit (100); the power converter mode switching control method includes the following steps: Step 1: The power converter is powered on and starts to output; Step 2: When the resonance number of the AC waveform is less than 1, the working mode of the power converter is CCM mode power supply; Step 3: When the resonance number of the AC waveform is greater than or equal to 1 and less than or equal to 4, the working mode of the power converter is QR mode; Step 4: When the resonance number of the AC waveform is greater than 4, the working mode of the power converter is DCM mode.

2. The power converter mode switching control method according to claim 1, wherein In Step 1: The power conversion control unit (100) is powered on to output a voltage to the G pole of the power transistor (140), and then stores energy through the excitation of the transformer (110); when the power transistor (140) is turned off, the transformer (110) demagnetizes and transfers energy to the output feedback circuit (120) and the output rectifying and filtering circuit (130); after the demagnetization energy transfer of the transformer (110) is completed, the excitation inductor of the transformer (110) and the junction capacitance LC of the power transistor (140) resonate to generate an alternating current on the input side of the transformer (110), and the alternating current is input to the D pole of the power transistor (140) again, and so on.

3. The power converter mode switching control method according to claim 2, wherein In Step 2: When the AC waveform resonance number on the output side of the transformer (110) is less than 1, that is, the AC waveform resonance number of the feedback signal FB of the output feedback circuit (120) is less than 1, the feedback signal FB is output to the power conversion control unit (100). The power transistor conversion control unit (100) controls the voltage level of the G pole of the power transistor (140) according to the feedback signal FB. The transformer (110) reciprocally magnetizes to store energy and demagnetizes to output energy, and the system operates in the CCM mode.

4. The power converter mode switching control method according to claim 2, characterized in that In Step 3: When the AC waveform resonance number on the output side of the transformer (110) is greater than or equal to 1 and less than or equal to 4, that is, the AC waveform resonance number of the feedback signal FB of the output feedback circuit (120) is greater than or equal to 1 and less than or equal to 4, the feedback signal FB is output to the power conversion control unit (100). The power transistor conversion control unit (100) controls the voltage level of the G pole of the power transistor (140) according to the feedback signal FB. The transformer (110) reciprocally magnetizes to store energy and demagnetizes to output energy, and the system operates in the QR mode.

5. The power converter mode switching control method according to claim 2, characterized in that In Step 4: When the AC waveform resonance number on the output side of the transformer (110) is greater than 4, that is, the AC waveform resonance number of the feedback signal FB of the output feedback circuit (120) is greater than 4, the feedback signal FB is output to the power conversion control unit (100). The power transistor conversion control unit (100) controls the voltage level of the G pole of the power transistor (140) according to the feedback signal FB. The transformer (110) reciprocally magnetizes to store energy and demagnetizes to output energy, and the system operates in the DCM mode.

6. The power converter mode switching control method according to any one of claims 1 to 5, characterized in that, The output feedback circuit (120) includes a resistor R1 and a resistor R2. One end of the resistor R1 is connected to one side of the output side of the transformer 110. The other end of the resistor R1 is connected to the resistor R2 and the second input terminal of the power transistor conversion control unit (100). The other end of the resistor R2 is grounded, and the other side of the output side of the transformer (110) is grounded.

7. The power converter mode switching control method according to any one of claims 1 to 5, characterized in that, The power conversion control unit (100) includes a power transistor conduction trigger circuit (150), a comparator (151), a shaping circuit (152), a combinational logic circuit (153), a power transistor turn-off trigger circuit (154), a flip-flop (155), and a power transistor drive circuit (156). The output terminal of the power transistor conduction trigger circuit (150) is connected to the input terminal of the combinational logic circuit (153). The output terminal of the comparator (151) is connected to the input terminal of the shaping circuit (152). The output terminal of the shaping circuit (152) is connected to the input terminal of the combinational logic circuit (153). The output terminal of the combinational logic circuit (153) is connected to the input terminal of the flip-flop (155). The output terminal of the power transistor turn-off trigger circuit (154) is connected to the input terminal of the flip-flop (155). The output terminal of the flip-flop (155) is connected to the input terminal of the power transistor drive circuit (156). The input terminal of the power transistor conduction trigger circuit (150) is connected to the non-inverting input terminal of the comparator (151) and the output terminal of the feedback circuit (120). The inverting input terminal of the comparator (151) is connected to the reference voltage source V01. The input terminal of the power transistor turn-off trigger circuit (154) is connected to the S pole of the power transistor (140). The output terminal of the power transistor drive circuit (156) is connected to the G pole of the power transistor (140).

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