Power converter, method of controlling a power converter and controller

Abstract

A power converter, a method of controlling the power converter and a controller, the power converter comprising a transformer, a resonant circuit, a switching circuit and an auxiliary circuit. The transformer comprises a primary winding disposed on a primary side of the transformer, a magnetizing inductor in parallel with the primary winding, and a secondary winding disposed on a secondary side of the transformer and coupled to the primary winding. The resonant circuit is coupled to the primary winding. The switching circuit comprises a first switch and a second switch connected in series with the first switch. The resonant circuit is coupled between the first switch and the second switch. The auxiliary circuit disposed on the primary side comprises an auxiliary winding, an auxiliary switch coupled to the auxiliary winding, and an auxiliary capacitor connected in series with the auxiliary switch. The auxiliary switch is turned on to cause the auxiliary capacitor to charge the magnetizing inductor to generate a magnetizing current, and the magnetizing current is to turn on a parasitic diode of the first switch. The power converter is to achieve zero voltage switching in a discontinuous resonant mode.

Description

Technical Field

[0001] This case relates to a power converter, and more particularly to a power converter suitable for achieving zero-voltage switching in discontinuous resonant mode, and a controller for controlling the power converter. Background Technology

[0002] As consumer electronics products increasingly demand higher power and smaller adapter sizes, switching power converters, with their high efficiency and compact size, have replaced linear regulators as the mainstream technology in consumer electronics applications.

[0003] Traditional switching power converters typically use metal-oxide-semiconductor field-effect transistors (MOSFETs) as the switching elements for pulse width modulation (PWM). This is because MOSFETs have characteristics such as fast switching speed and low loss. However, if the parasitic capacitance of the MOSFET's output is not fully discharged when the switch is turned on, a voltage will appear between the drain and source of the MOSFET. This voltage will cause a loss due to the current flowing through the MOSFET's source; this loss is called the MOSFET's switching loss.

[0004] To reduce switching losses, traditional asymmetric half-bridge flyback converters typically continue to conduct the lower arm switch to reverse charge the magnetizing inductor when the magnetizing inductor discharges to 0 amperes (A), making the magnetizing inductor current reversed. This reverse current is then used to discharge the parasitic capacitance of the upper arm switch, achieving zero voltage switching. This mode is called continuous resonant mode.

[0005] While this continuous resonant mode works well under full-load, high-voltage conditions, the peak current of the magnetizing inductor decreases as the load or output voltage drops. This leads to excessively high operating frequencies, and the circulating energy of the resonant tank also limits the overall efficiency of the converter. Therefore, asymmetric half-bridge flyback converters typically use discontinuous resonant mode with discontinuous magnetizing inductor current when the load decreases or the output voltage is low. However, since the switching in discontinuous resonant mode is completed when the magnetizing inductor discharges to zero, there is no reverse magnetizing current, making zero-voltage switching impossible and resulting in additional switching losses. Therefore, how to provide power conversion to solve these problems is an important issue in this field. Summary of the Invention

[0006] A power converter includes a transformer, a resonant circuit, a switching circuit, and an auxiliary circuit. The transformer includes a primary winding disposed on the primary side of the transformer, a magnetizing inductor connected in parallel with the primary winding, and a secondary winding disposed on the secondary side of the transformer and coupled to the primary winding. The resonant circuit couples the primary winding. The switching circuit includes a first switch and a second switch connected in series with the first switch, wherein the resonant circuit is coupled between the first switch and the second switch. The auxiliary circuit disposed on the primary side includes an auxiliary winding, an auxiliary switch coupled to the auxiliary winding, and an auxiliary capacitor connected in series with the auxiliary switch. When the auxiliary switch is open, the magnetizing inductor discharges to charge the auxiliary capacitor; when the auxiliary switch is closed, the auxiliary capacitor charges the magnetizing inductor, generating a magnetizing current that turns on the parasitic diode of the first switch.

[0007] This disclosure provides another power converter, wherein a first switch includes a first parasitic capacitor, the capacitance of which is less than the energy storage capacitance of an auxiliary capacitor.

[0008] This disclosure provides another power converter in which a second switch includes a second parasitic capacitor, the value of which is smaller than the value of the energy storage capacitor.

[0009] This disclosure provides another power converter in which the input voltage charges the magnetizing inductor when a first switch is on and a second switch is off.

[0010] This disclosure provides another power converter in which energy is transferred from the primary winding to the secondary winding when the first switch is open and the second switch is on.

[0011] This disclosure provides another power converter in which, when the first switch is open and the second switch is open, and the magnetizing inductor is de-energized to zero, the magnetizing inductor, the first parasitic capacitance, and the second parasitic capacitance generate a resonance with a resonant period.

[0012] This disclosure provides another power converter in which the resonant period is positively correlated with the output voltage value on the secondary side.

[0013] This disclosure provides another power converter in which the excitation current value is calculated according to the following formula:

[0014]

[0015] Among them I MAGneg The excitation current value, V PFC Input voltage value, Coss s1 The capacitance value of the first parasitic capacitance, Coss s2 The capacitance value of the second parasitic capacitance, and L m This is the magnetizing inductance value.

[0016] This disclosure provides another power converter in which an auxiliary switch includes an auxiliary parasitic capacitor, the capacitance of which is less than that of a first parasitic capacitor.

[0017] This disclosure provides another power converter in which the drive loss P of the auxiliary switch is reduced. gate It is based on the following formula:

[0018] P gate =0.5·Ciss·V gate 2 ·f sw

[0019] Where Ciss is the capacitance value of the auxiliary parasitic capacitance, V gate For the gate voltage of the auxiliary switch, and f sw This refers to the operating frequency.

[0020] This disclosure provides another power converter in which the voltage stress of the auxiliary switch is proportional to the ratio of the number of turns of the primary winding to the number of turns of the auxiliary winding.

[0021] This disclosure provides another power converter in which a first end of an auxiliary capacitor is coupled to a first end of an auxiliary winding, a second end of the auxiliary capacitor is coupled to a first end of an auxiliary switch, and a second end of the auxiliary switch is coupled to a second end of the auxiliary winding.

[0022] This disclosure provides another power converter, wherein the auxiliary switch is a transistor of a first size and the first switch is a transistor of a second size, wherein the first size is smaller than the second size.

[0023] This disclosure provides another power converter in which the second switch is a transistor of a third size, the third size being larger than the first size.

[0024] A control method for a power converter, wherein the power converter includes a switching circuit having a first switch and a second switch, a transformer having a primary winding, a magnetizing inductor, and a secondary winding, a resonant circuit coupled between the primary winding and the switching circuit, and an auxiliary circuit having an auxiliary winding, an auxiliary switch, and an auxiliary capacitor, wherein the auxiliary circuit and the primary winding are located on the same side of the transformer. The control method includes turning on the second switch and charging the auxiliary capacitor by discharging the magnetizing inductor for a first period; in a second period after the first period, turning off the second switch and turning on the auxiliary switch, causing the auxiliary capacitor to charge the magnetizing inductor and generate a magnetizing current; and in a third period after the second period, turning off the auxiliary switch and turning on the parasitic diode of the first switch by allowing the magnetizing current to flow through it.

[0025] This disclosure provides another control method for a power converter, further comprising: during an energy release period between a first period and a second period, disconnecting the first switch and the second switch's energy release magnetizing inductor; and during a resonance period after the energy release period and before the second period, generating a resonance with a resonant period through the magnetizing inductor, the first parasitic capacitance of the first switch, and the second parasitic capacitance of the second switch.

[0026] This disclosure provides another method for controlling a power converter, wherein the current flowing through the magnetizing inductor is zero at the end of the resonance period.

[0027] This disclosure provides another method for controlling a power converter, wherein the second period is shorter than the first period.

[0028] This disclosure provides another control method for a power converter, wherein the ratio of the number of turns of the primary winding to the number of turns of the auxiliary winding is greater than 1.

[0029] This disclosure provides another control method for a power converter, further comprising: during a first period, disconnecting a first switch and turning on a second switch to transfer energy from the primary winding to the secondary winding.

[0030] A controller is provided for controlling a power converter, wherein the power converter includes a switching circuit having a first switch and a second switch, a transformer having a primary winding, a magnetizing inductor, and a secondary winding, a resonant circuit coupled between the primary winding and the switching circuit, and an auxiliary circuit having an auxiliary winding, an auxiliary switch, and an auxiliary capacitor, wherein the auxiliary circuit and the primary winding are located on the same side of the transformer. The controller is configured to: turn on the second switch and charge the auxiliary capacitor by discharging the magnetizing inductor for a first period; in a second period following the first period, turn off the second switch and turn on the auxiliary switch, causing the auxiliary capacitor to charge the magnetizing inductor and generate a magnetizing current; and in a third period following the second period, turn off the auxiliary switch and turn on the first switch by allowing the magnetizing current to flow through the first switch, turning on the parasitic diode of the first switch. Attached Figure Description

[0031] To make the above and other objects, features, advantages and embodiments of this disclosure more apparent and understandable, the accompanying drawings are described below:

[0032] Figure 1 This is a schematic diagram of a power converter and controller according to an embodiment of the present disclosure;

[0033] Figure 2 This is illustrated according to an embodiment of the present invention. Figure 1 A flowchart of the control method for the power converter;

[0034] Figure 3This is a waveform diagram of multiple signals of a power converter illustrated according to an embodiment of this case;

[0035] Figures 4 to 10 This is illustrated according to an embodiment of the present invention. Figure 1 A schematic diagram of the power converter operating during each period;

[0036] Figure 11 This is a schematic diagram of a power converter according to another embodiment of the present disclosure.

[0037] [Symbol Explanation]

[0038] 100: Power Converter

[0039] 110: Switching circuit

[0040] 120: Resonant Circuit

[0041] 130: Auxiliary Circuit

[0042] 140: Primary Side

[0043] 150: Secondary side

[0044] 160: Controller

[0045] 200: Control method of power converter

[0046] 300: Waveform diagrams of multiple signals

[0047] 400: Power Converter

[0048] C1: Parasitic capacitance

[0049] C2: Parasitic capacitance

[0050] C a Auxiliary parasitic capacitance

[0051] C b Auxiliary capacitor

[0052] C O :capacitance

[0053] C r :capacitance

[0054] D1: Parasitic diode

[0055] D2: Parasitic diode

[0056] D a Parasitic diode

[0057] D O :diode

[0058] I a Current

[0059] I ar Reverse current

[0060] I Lm Magnetizing current

[0061] I Lr Current

[0062] I o Current

[0063] L m Magnetizing inductor

[0064] L r :inductance

[0065] N1: Primary winding

[0066] N2: Secondary winding

[0067] N a Auxiliary winding

[0068] n1: Node

[0069] R L :load

[0070] S1: Switch

[0071] S2: Switch

[0072] S a Auxiliary switch

[0073] t: time

[0074] t1: Time point

[0075] t2: Time point

[0076] t3: Time point

[0077] t4: Time point

[0078] t5: Time point

[0079] t6: Time point

[0080] t7: Time point

[0081] t8: Time point

[0082] TX: Transformer

[0083] V a :Voltage

[0084] V gs_HS :Signal

[0085] V gs_LS:Signal

[0086] V gs_Sa :Signal

[0087] V HB :Voltage

[0088] V O Output voltage

[0089] V PFC Input voltage

[0090] S210: Steps

[0091] S220: Steps

[0092] S230: Steps

[0093] S240: Steps

[0094] S250: Steps

[0095] S260: Steps

[0096] S270: Steps Detailed Implementation

[0097] The following is a detailed description of embodiments in conjunction with the accompanying drawings. However, the provided embodiments are not intended to limit the scope of this disclosure, and the description of the structural operation is not intended to limit the order of execution. Any structure resulting from the recombination of elements and producing a device with equivalent functionality is within the scope of this disclosure. Furthermore, the illustrations are for illustrative purposes only and are not drawn to their original dimensions. For ease of understanding, the same or similar elements will be labeled with the same symbols in the following description.

[0098] The terms “coupled,” “coupled,” or “connected” as used in this article may refer to two or more components making direct physical or electrical contact with each other, or making indirect physical or electrical contact with each other, or to two or more components operating or moving together.

[0099] In this article, the term "circuit" is used to refer to an object consisting of one or more transistors and / or one or more active and passive components connected in a certain manner to process signals.

[0100] Unless otherwise specified, the terms used throughout this specification and claims generally have their ordinary meaning in the context of the art, the disclosure, and the specific content. Furthermore, the terms "comprising," "including," "having," "containing," etc., as used herein are open-ended terms, meaning "including but not limited to." Additionally, the term "and / or" as used herein includes any one or more of the related listed items and all combinations thereof.

[0101] Please see Figure 1 , Figure 1 This is a schematic diagram of a power converter 100 and a controller 160 according to an embodiment of this disclosure. Figure 1 As shown, the power converter 100 includes a switching circuit 110, a resonant circuit 120, an auxiliary circuit 130, a transformer TX, and a diode D. O and capacitor C O In some embodiments, the power converter 100 couples the load R L And used to determine the input voltage V received by the switching circuit 110. PFC Generate output to load R L Output voltage V O In some embodiments, diode D O It can be replaced by a metal oxide semiconductor field-effect transistor (MOSFET). In some embodiments, the controller 160 is used to generate signals to control the operation of the power converter and can be a microprocessor or any suitable integrated circuit.

[0102] In some embodiments, the transformer TX includes a primary winding N1 and a magnetizing inductance L. m And the secondary winding N2. The primary winding N1 is located on the primary side 140 of transformer TX, and the secondary winding N2 is located on the secondary side 150 of transformer TX. For example... Figure 1 As shown, the switching circuit 110, resonant circuit 120, and auxiliary circuit 130 are located on the primary side 140. Diode D O Capacitor C O Load R L Located on the secondary side 150.

[0103] In some embodiments, the switching circuit 110 includes a switch S1 and a switch S2. Switch S1 includes a parasitic capacitance C1 and a parasitic diode D1, and responds to a signal V received at its gate terminal. gs_HS It switches the circuit to either turn the circuit on or off. Switch S2 includes a parasitic capacitance C2 and a parasitic diode D2, and responds to a signal V received at its gate. gs_LS It switches between on and off states. Switch S1 is coupled to the input voltage V. PFC The positive input terminal is connected to node n1 between switches S1 and S2. Switch S2 is coupled between node n1 and the ground terminal.

[0104] In some embodiments, the resonant circuit 120 includes an inductor L r With capacitor C r Inductor L rCoupled between the (circular) dot end of the primary winding N1 and node n1, and at the dot end of the primary winding N1 and the magnetizing inductor L m One end is coupled. Capacitor C r Coupled between the non-point terminal and the ground terminal of the primary winding N1, and connected to the magnetizing inductor L at the non-point terminal of the primary winding N1. m The other end is coupled. In some embodiments, the inductor L... r This refers to the leakage inductance or independent inductance of the transformer TX.

[0105] In some embodiments, the auxiliary circuit 130 includes an auxiliary switch S a With auxiliary capacitor C b and auxiliary winding N a Auxiliary switch S a Including auxiliary parasitic capacitance C a With parasitic diode D a and in response to the signal V received at its gate terminal. gs_Sa To switch between on and off states. Auxiliary switch S a Coupled in auxiliary winding N a Between the (circular) dot end and the ground end. Auxiliary capacitor C b Coupled in auxiliary winding N a Between the non-point terminal and the ground terminal. In some embodiments, the capacitance value of parasitic capacitance C1 is smaller than that of auxiliary capacitance C. b The capacitance value (also known as the "energy storage capacitance value"). In some embodiments, the capacitance value of the parasitic capacitance C2 is smaller than that of the auxiliary capacitance C. b The capacitance value. In some embodiments, the auxiliary parasitic capacitance C a The capacitance value is less than the capacitance value of the parasitic capacitance C1. In some embodiments, the auxiliary parasitic capacitance C... a The capacitance value is less than the capacitance value of the parasitic capacitance C2.

[0106] Regarding the coupling relationship on the secondary side at 150°, diode D O The positive terminal and capacitor C O One end is coupled to the ground terminal, diode D O The negative terminal is coupled to the (circular) dot terminal of the secondary winding N2. Capacitor C O The other end is coupled to the non-point end of the secondary winding N2.

[0107] Please refer to the following: Figure 2 , Figure 3 as well as Figures 4 to 10 . Figure 2 This is illustrated according to an embodiment of the present invention. Figure 1 A flowchart of the control method 200 for the power converter 100. Figure 3This is a waveform diagram 300 of a plurality of signals of a power converter 100 illustrated according to an embodiment of the present invention. Figures 4 to 10 This is illustrated according to an embodiment of the present invention. Figure 1 A schematic diagram of the power converter 100 operating during various periods. In some embodiments, the controller 160 executes control method 200 to control the operation of the power converter 100.

[0108] According to step S210, during the period from time point t1 to t2, such as Figure 3 and Figure 4 As shown, switch S1 responds to a signal V with a high potential. gs_HS The circuit is turned on, and the switch S2 and auxiliary switch S2 are connected. a Responding to a low-potential signal V gs_LS and V gs_Sa Disconnect (switch off). Node n1 has a voltage V. HB Voltage V HB Response input voltage V PFC The pull is related to the inductor L r and excitation inductance L m Charging causes current to flow through inductor L r and excitation inductance L m Current I Lr and excitation current I Lm Rise. Magnetizing inductance L m Through the excitation current I Lm Discharging parasitic capacitance C1 and discharging capacitance C r Charging. In some embodiments, when the excitation current I... Lm After rising to the set value, signal V gs_HS Switch to a low potential to disconnect switch S1.

[0109] In addition, Figure 4 In the embodiment, diode D O It is in an open state in response to its positive terminal being grounded and its negative terminal being at a low potential. Specifically, the terminals of the primary winding N1 and the secondary winding N2 are at a high potential, therefore, the diode D coupled to the terminal of the secondary winding N2... O The negative terminal of diode D is at a high potential, while diode D... O The positive terminal of diode D is grounded, making diode D O disconnect.

[0110] According to step S220, during the period from time point t2 to t3, such as Figure 5 As shown, switch S1 responds to a signal V with a low potential. gs_HS Disconnect, and switch S2, auxiliary switch S a and diode D OMaintain disconnection. Magnetizing current I Lm This discharges the parasitic capacitance C2. Once the parasitic capacitance C2 has completely discharged, the magnetizing current I... Lm The current flows through the conducting parasitic diode D2, making the switching loss of switch S2 almost zero. Then, signal V... gs_LS Switch to a high potential to turn on switch S2.

[0111] According to step S230, during the period from time point t3 to t4, such as Figure 6 As shown, switch S2 responds to a signal V with a high potential. gs_LS The circuit is turned on, and the switch S1 and the auxiliary switch S1 are connected. a Keep disconnected. Capacitor C r The discharge generates a current flowing through the primary winding N1, transferring energy from the primary winding N1 to the secondary winding N2. In response to this energy transfer from the primary winding N1 to the secondary winding N2, diode D... O The circuit is turned on and a current I is generated in the secondary winding N2. o In addition, energy from the primary winding N1 is also transferred to the auxiliary winding N. a To generate current I a Current I a Flow through parasitic diode D a And regarding the auxiliary capacitor C b Charge.

[0112] According to step S240, during the period from time point t4 to t5 (which can be considered the "energy release period"), such as Figure 7 As shown, switch S2 responds to a signal V with a low potential. gs_LS Disconnect, and switch S1 and auxiliary switch S a Maintain disconnection. Flow through inductor L r And excitation inductance L m Current I Lr and excitation current I Lm The current continues to decrease until it reaches zero (in other words, the magnetizing inductance L) m (Energy released to zero). During the energy release period, no energy is transferred from the primary winding N1 to the auxiliary winding N. a Therefore, diode D O disconnect.

[0113] According to step S250, during the period from time point t5 to t6 (which can be considered the "resonance period"), such as Figure 8 As shown, switch S1, switch S2, and auxiliary switch S a and diode D O Maintain disconnection. Magnetizing inductance L m The parasitic capacitances C1 and C2 generate a resonance with a resonant period. When the resonance reaches a sufficient number of resonant periods and current flows through the inductor L...r Current I Lr With the current flowing through the magnetizing inductor L m excitation current I Lm When the current value is zero, the signal V gs_Sa Switch to high potential to turn on auxiliary switch S a In some embodiments, the number of resonant periods is related to the output voltage V. O They are positively correlated.

[0114] According to step S260, during the period from time point t6 to t7, such as Figure 9 As shown, auxiliary switch S a In response to a high potential signal V gs_Sa The circuit is turned on, as are switches S1 and S2 and diode D. O Maintain disconnection. Auxiliary capacitor C b Energy release generates reverse current I ar To the excitation inductor L m Reverse energy storage causes the excitation current I to... Lm Reverse current value I MAGneg In some embodiments, the reverse current value I MAGneg The corresponding reverse current value I is the current value that can completely discharge parasitic capacitor C1 and completely charge parasitic capacitor C2. MAGneg It is based on formula (1):

[0115]

[0116] Coss s1 The capacitance value representing the parasitic capacitance C1, Coss s2 The capacitance value of parasitic capacitance C2, V PFC Represents input voltage V PFC Voltage value and L m Represents magnetizing inductance L m The inductance value. In some embodiments, when the excitation current I... Lm Reverse current value I MAGneg At that time, signal V gs_Sa Switch to low potential to disconnect auxiliary switch S a .

[0117] As described above, due to the auxiliary switch S a The operation is used to control the magnetizing inductor L m Energy storage, therefore, in some embodiments, auxiliary switch S a The transistor size is smaller than the transistor size of switch S1. In other words, the auxiliary parasitic capacitance C a The capacitance value is lower than the parasitic capacitance C1, which also reduces the capacitance of the auxiliary switch S. a driving loss P gateAuxiliary switch S a Drive loss P gate It is based on formula (2):

[0118] P gate =0.5·Ciss·V gate 2 ·f sw …(2)

[0119] Ciss represents the auxiliary parasitic capacitance C. a capacitance value, V gate Representative auxiliary switch S a Gate voltage value and f sw Representative auxiliary switch S a Operating frequency.

[0120] In some embodiments, the auxiliary switch S a The transistor size is smaller than the transistor size of switch S2.

[0121] In some embodiments, the auxiliary switch S a Voltage stress and primary winding N1 and auxiliary winding N a The number of turns is proportional. For example, a number of turns ratio of 200% (the primary winding N1 has 20 turns, and the auxiliary winding N...) a The voltage stress magnitude is when the number of turns is 10 (the primary winding N1 has 10 turns, and the auxiliary winding N...). a The number of laps is half of 10.

[0122] In some embodiments, the auxiliary switch S a Switching overhead P sw It is based on formula (3):

[0123] P sw =0.5·I d ·V ds ·(t on +t off )·f sw …(3)

[0124] I d Representative auxiliary switch S a Drain current value, V ds Representative auxiliary switch S a The trans-voltage between the drain and source, t on With t off These represent auxiliary switches S respectively. a Startup time and shutdown time and f sw This represents the operating frequency.

[0125] In some embodiments, the period from time point t6 to t7 is shorter than the period from time point t3 to t4.

[0126] According to step S270, during the period from time point t7 to t8, such as Figure 10 As shown, auxiliary switch S a In response to a low potential signal V gs_Sa Disconnect switch S2 and diode D O Maintain disconnection. Magnetizing current I Lm As current I Lr Discharge the parasitic capacitance C1. When the parasitic capacitance C1 has completely discharged, the current I... Lm The current flows through the conducting parasitic diode D1, causing switch S1 to conduct with almost zero switching losses, achieving zero-voltage switching (ZVS). Then, signal V... gs_HS Switch to high potential to turn on switch S1.

[0127] Please see Figure 11 , Figure 11 This is a schematic diagram of a power converter 400 according to an embodiment of the present disclosure. Compared to Figure 1 Power converter 100, inductor L r The point terminal of the primary winding N1 is coupled to the input voltage V. PFC Between the positive input terminals. Capacitor C r It is coupled between the non-point end of the primary winding N1 and node n1.

[0128] In summary, the power converter and its control method disclosed herein enable the power converter to achieve zero-voltage switching even in discontinuous resonant mode, thereby reducing switching losses in the power converter.

[0129] Although the present disclosure has been described above with reference to embodiments, it is not intended to limit the present disclosure. Any person skilled in the art may make various modifications and refinements without departing from the spirit and scope of the present disclosure. Therefore, the scope of protection of the present disclosure shall be determined by the appended claims.

Claims

1. A power converter, characterized in that, include: A transformer, comprising: A primary winding is provided on the primary side of the transformer; A magnetizing inductor, connected in parallel to the primary winding; and A primary winding is provided on the primary side of the transformer and coupled to the primary winding; a resonant circuit is coupled to the primary winding. A switching circuit, including: A first switch; and A second switch, connected in series with the first switch, wherein the resonant circuit is coupled between the first switch and the second switch; and An auxiliary circuit, disposed on the primary side, includes; One auxiliary winding; An auxiliary switch, coupling the auxiliary winding; and An auxiliary capacitor is connected in series with the auxiliary switch, wherein the auxiliary switch is turned off and the magnetizing inductor is discharged to charge the auxiliary capacitor; The auxiliary switch being turned on causes the auxiliary capacitor to charge the magnetizing inductor, generating a magnetizing current, which in turn turns on a parasitic diode of the first switch.

2. The power converter as described in claim 1, characterized in that, The first switch includes a first parasitic capacitor, the capacitance of which is less than the energy storage capacitance of the auxiliary capacitor.

3. The power converter as described in claim 2, characterized in that, The second switch includes a second parasitic capacitor, the capacitance of which is less than the value of the energy storage capacitor.

4. The power converter as described in claim 3, characterized in that, When the first switch is turned on and the second switch is turned off, an input voltage charges the magnetizing inductor.

5. The power converter as described in claim 4, characterized in that, When the first switch is open and the second switch is on, the energy of the primary winding is transferred to the secondary winding.

6. The power converter as described in claim 4, characterized in that, When the first switch is open and the second switch is open, and the magnetizing inductor is released to zero, the magnetizing inductor, the first parasitic capacitance, and the second parasitic capacitance generate a resonance with a resonant period.

7. The power converter as described in claim 6, characterized in that, The resonant period is positively correlated with the output voltage value on the secondary side.

8. The power converter as described in claim 3, characterized in that, The excitation current value is calculated according to the following formula: Among them I MAGneg The excitation current value, V PFC For an input voltage value, Coss s1 The capacitance value of the first parasitic capacitance, Coss s2 The capacitance value of the second parasitic capacitor, and L m This is the magnetizing inductance value of the magnetizing inductor.

9. The power converter as described in claim 2, characterized in that, The auxiliary switch includes an auxiliary parasitic capacitor, the capacitance of which is less than that of the first parasitic capacitor.

10. The power converter as claimed in claim 9, characterized in that, The driving loss P of the auxiliary switch gate It is based on the following formula: P gate =0.5·Ciss·V gate 2 ·f sw Where Ciss is the capacitance value of the auxiliary parasitic capacitance, V gate The gate voltage of the auxiliary switch, and f sw This is an operating frequency.

11. The power converter as claimed in claim 1, characterized in that, The voltage stress of the auxiliary switch is proportional to the ratio of the number of turns of the primary winding to the number of turns of the auxiliary winding.

12. The power converter as claimed in claim 1, characterized in that, The auxiliary capacitor has a first terminal coupled to a first terminal of the auxiliary winding, a second terminal coupled to a first terminal of the auxiliary switch, and a second terminal coupled to a second terminal of the auxiliary winding.

13. The power converter as claimed in claim 1, characterized in that, The auxiliary switch is a transistor of a first size and the first switch is a transistor of a second size, wherein the first size is smaller than the second size.

14. The power converter as claimed in claim 13, characterized in that, The second switch is a transistor of a third size, which is larger than the first size.

15. A control method for a power converter, characterized in that, The power converter includes a switching circuit with a first switch and a second switch, a transformer with a primary winding, a magnetizing inductor, and a secondary winding, a resonant circuit coupled between the primary winding and the switching circuit, and an auxiliary circuit with an auxiliary winding, an auxiliary switch, and an auxiliary capacitor, wherein the auxiliary circuit and the primary winding are located on the same side of the transformer, and the control method includes: The second switch is turned on, and the auxiliary capacitor is charged for a first period by discharging the magnetizing inductor. In a second period following the first period, the second switch is turned off and the auxiliary switch is turned on, causing the auxiliary capacitor to charge the magnetizing inductor and generate a magnetizing current; and In a third period following the second period, the auxiliary switch is disconnected, and the excitation current flows through the first switch to turn on a parasitic diode of the first switch.

16. The control method as described in claim 15, characterized in that, Further includes: During a release period between the first period and the second period, the first switch and the second switch are disconnected to release the magnetizing inductor; as well as During a resonance period following the energy release period and preceding the second period, a resonance with a resonance period is generated by the magnetizing inductor, a first parasitic capacitance of the first switch, and a second parasitic capacitance of the second switch.

17. The control method as described in claim 16, characterized in that, At the end of the resonance period, the current flowing through the magnetizing inductor is zero.

18. The control method as described in claim 15, characterized in that, The second period is shorter than the first period.

19. The control method as described in claim 15, characterized in that, The ratio of the number of turns of the primary winding to that of the auxiliary winding is greater than 1.

20. The control method as described in claim 15, characterized in that, Further includes: During the first period, the first switch is turned off and the second switch is turned on, so that the energy of the primary winding is transferred to the secondary winding.

21. A controller for controlling a power converter, characterized in that, The power converter includes a switching circuit with a first switch and a second switch, a transformer with a primary winding, a magnetizing inductor, and a secondary winding, a resonant circuit coupled between the primary winding and the switching circuit, and an auxiliary circuit with an auxiliary winding, an auxiliary switch, and an auxiliary capacitor, wherein the auxiliary circuit and the primary winding are located on the same side of the transformer. The controller is used to execute: The second switch is turned on, and the auxiliary capacitor is charged for a first period by discharging the magnetizing inductor. During a second period following the first period, the second switch is turned off and the auxiliary switch is turned on, causing the auxiliary capacitor to charge the magnetizing inductor and generate a magnetizing current. as well as In a third period following the second period, the auxiliary switch is disconnected, and the excitation current flows through the first switch, turning on a parasitic diode of the first switch and then turning on the first switch.

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