A soft-switching converter

Abstract

This invention relates to a soft-switching converter, comprising a main circuit and a soft-switching auxiliary circuit. The soft-switching auxiliary circuit includes power devices Q3 and Q4, diodes D1, D2, and D3, inductor L2, and coupling inductor L3. Compared with existing technologies, this invention adds a soft-switching auxiliary circuit connected to the main circuit. Through auxiliary circuit control, the semiconductor devices in the main circuit and the soft-switching auxiliary circuit can achieve soft-switching effects across the entire load range and the entire input voltage range without stress spikes, thereby improving the operating frequency, power density, and efficiency of the switching converter, reducing size, EMI, and cost.

Description

Technical Field

[0001] This invention relates to the field of power supply circuits, and particularly to BUCK and BOOST switching converters for soft-switching control. Background Technology

[0002] With the development of power supply technology, high-efficiency, high-power-density synchronous rectifier circuits have become a trend, such as... Figure 1 and Figure 2 As shown, Figure 1 For existing synchronous BUCK converters, Figure 2 For existing synchronous boost converters, the switching process and drive losses of the power MOSFETs are becoming increasingly prominent. With increasing switching frequency, the switching and drive losses of the power MOSFETs increase proportionally, reducing the efficiency of the synchronous rectifier circuit and exacerbating electromagnetic interference (EMI) problems. To address this issue, soft-switching technology has been developed and is gradually being applied in switching converters to reduce switching losses and EMI noise, and improve the converter's power density. Ideally, soft-switching technology involves first reducing the current or voltage of the switching transistor to zero during the switching process, and then allowing the voltage or current to rise slowly, so that the switching losses are approximately zero.

[0003] For example, Chinese patent application number CN202111560022.X proposes a soft-switching bidirectional BUCK-BOOST converter. Please refer to [the relevant documentation]. Figure 1 This converter, by adding an auxiliary soft-switching circuit, can achieve soft switching of the main power transistors of the BUCK and BOOST converters without stress spikes. However, through actual analysis and simulation verification, it was found that the coupling transformer in its soft-switching auxiliary circuit lacks a demagnetizing circuit. As a result, all the energy stored in the coupling transformer is converted into voltage spikes, which are applied to the semiconductor devices in the soft-switching auxiliary circuit. This causes voltage spikes to be generated that are several times higher than the input voltage of the BUCK converter or the output voltage of the BOOST converter, making it difficult to apply in actual products. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to propose a soft-switching converter and its control method, which can solve the problem of large stress spikes in semiconductor devices in the soft-switching auxiliary circuit of the prior art, and can realize the soft-switching effect of semiconductor devices in the main circuit and the soft-switching auxiliary circuit without stress spikes in the full load range and the full input voltage range.

[0005] The technical solution adopted in this invention is as follows:

[0006] On one hand, a soft-switching converter is provided, including a main circuit, which includes a power transistor Q1, a power transistor Q2, an inductor L1, and a capacitor C1; the first end of the power transistor Q1 is used to connect to the positive terminal of the power supply, the second end of the power transistor Q1 is connected to one end of the inductor L1 and the first end of the power transistor Q2, the other end of the inductor L1 is connected to one end of the capacitor C1, and the second end of the power transistor Q2 is connected to the other end of the capacitor C1 and is used to connect to the negative terminal of the power supply;

[0007] It also includes a soft-switching auxiliary circuit, which includes power device Q3, power device Q4, diodes D1, D2, and D3, inductor L2, and coupling inductor L3; the first terminal of power device Q3 is connected to both the cathode of diode D2 and the first terminal of power transistor Q1; the second terminal of power device Q3 is connected to both the first terminal of coupling inductor L3 and the cathode of diode D3; the second terminal of coupling inductor L3 is connected to the anode of diode D1, and the third terminal of coupling inductor L3 is connected to both the first terminal of power device Q4 and the anode of diode D2; the cathode of diode D1 is connected to one end of inductor L2, and the other end of inductor L2 is connected to the first terminal of power transistor Q2; the second terminal of power device Q4 is connected to both the anode of diode D3 and the negative terminal of the power supply.

[0008] Preferably, the coupling inductor L3 includes a first inductor and a second inductor, the first end being the opposite-named end of the first inductor, the second end being the node connecting the same-named end of the first inductor and the opposite-named end of the second inductor, and the third end being the same-named end of the second inductor; the number of turns of the first inductor and the second inductor are equal.

[0009] Preferably, the power device Q3 is a MOSFET, an IGBT, or a diode; when the power device Q3 is a MOSFET or an IGBT, the first terminal of the power device Q3 is the drain and the second terminal is the source; when the power device Q3 is a diode, the first terminal of the power device Q3 is the cathode and the second terminal is the anode.

[0010] Preferably, the power device Q4 is a MOSFET, an IGBT, or a diode; when the power device Q4 is a MOSFET or an IGBT, the first terminal of the power device Q4 is the drain and the second terminal is the source; when the power device Q4 is a diode, the first terminal of the power device Q4 is the cathode and the second terminal is the anode.

[0011] Preferably, both power transistors Q1 and Q2 are MOSFETs or IGBTs, with the first terminal of both power transistors Q1 and Q2 being the drain and the second terminal being the source.

[0012] Preferably, power transistors Q1 and Q2 are driven by complementary drive with dead time; during the turn-on period of power transistor Q2, power device Q3 is turned on, and during the turn-on period of power transistor Q1, power device Q3 is turned off.

[0013] Preferably, the drive signal connected to the control terminal of power device Q4 is the same as the drive signal connected to the control terminal of power device Q3.

[0014] On the other hand, a soft-switching converter is provided, including a main circuit. The main circuit includes a power transistor Q1, a power transistor Q2, an inductor L1, and a capacitor C1. The first end of the power transistor Q1 is connected to one end of the capacitor C1, and the second end of the power transistor Q1 is connected to both one end of the inductor L1 and the first end of the power transistor Q2. The other end of the inductor L1 is used to connect to the positive terminal of the power supply, and the second end of the power transistor Q2 is connected to both the other end of the capacitor C1 and the negative terminal of the power supply.

[0015] It also includes a soft-switching auxiliary circuit, which includes power device Q3, power device Q4, diodes D1, D2, and D3, inductor L2, and coupling inductor L3; the first terminal of power device Q3 is connected to both the cathode of diode D2 and the first terminal of power transistor Q1; the second terminal of power device Q3 is connected to both the first terminal of coupling inductor L3 and the cathode of diode D3; the second terminal of coupling inductor L3 is connected to the cathode of diode D1, and the third terminal of coupling inductor L3 is connected to both the first terminal of power device Q4 and the anode of diode D2; the anode of diode D1 is connected to one end of inductor L2, and the other end of inductor L2 is connected to the first terminal of power transistor Q2; the second terminal of power device Q4 is connected to both the anode of diode D3 and the negative terminal of the power supply.

[0016] The working principle of this invention will be analyzed in conjunction with specific embodiments, and will not be elaborated here. The beneficial effects of this invention are as follows:

[0017] 1. By designing the auxiliary soft-switching circuit and the parallel capacitor of the power transistor, all power transistors of the BUCK and BOOST switching converters can achieve soft turn-on and soft turn-off, reducing switching losses, improving converter efficiency, and eliminating stress spikes in the power transistors, making component selection simpler.

[0018] 2. The power transistors in the auxiliary soft-switching circuit can achieve near-zero current turn-on and zero current turn-off, reducing switching losses in the auxiliary circuit;

[0019] 3. The coupling inductor in the auxiliary soft-switching circuit is demagnetized by a diode, which can ensure effective reset of the coupling inductor. The power transistor in the auxiliary soft-switching circuit is free of stress spikes, and the component selection is simpler.

[0020] 4. The diode D1 added to the auxiliary soft-switching circuit can effectively prevent the inductor L2 from being reverse-magnetized, making the design simpler and more controllable. Attached Figure Description

[0021] Figure 1This is a schematic diagram of a conventional soft-switching bidirectional BUCK-BOOST converter.

[0022] Figure 2 The schematic diagram of an existing BUCK switch converter;

[0023] Figure 3 Schematic diagram of an existing BOOST switching converter;

[0024] Figure 4 Schematic diagram of the switching converter of the first embodiment of the present invention;

[0025] Figure 5 for Figure 4 Control timing and waveforms;

[0026] Figure 6 Schematic diagram of the switching converter according to the second embodiment of the present invention;

[0027] Figure 7 for Figure 6 The control timing and waveform. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] The inventive concept of this application is as follows:

[0030] By utilizing the coupling inductor L3 and power devices Q3 and Q4, all power transistors in the BUCK and BOOST switching converters achieve soft turn-on and soft turn-off. Demagnetizing diodes D2 and D3 are added to reset the magnetic flux of the coupling inductor. Simultaneously, to ensure controllable timing, a diode is added at the center tap of the coupling inductor to effectively prevent reverse magnetization. The invention is described below with reference to specific embodiments.

[0031] First Embodiment

[0032] Figure 4 This is a schematic diagram of a switching converter according to a first embodiment of the present invention. In this embodiment, a soft-switching converter is provided, including a main circuit. The main circuit includes a power transistor Q1, a power transistor Q2, an inductor L1, and a capacitor C1. The first end of the power transistor Q1 is used to connect to the positive terminal of the power supply. The second end of the power transistor Q1 is connected to one end of the inductor L1 and the first end of the power transistor Q2. The other end of the inductor L1 is connected to one end of the capacitor C1. The second end of the power transistor Q2 is connected to the other end of the capacitor C1 and is used to connect to the negative terminal of the power supply.

[0033] It also includes a soft-switching auxiliary circuit, which includes power device Q3, power device Q4, diodes D1, D2, and D3, inductor L2, and coupling inductor L3; the first terminal of power device Q3 is connected to both the cathode of diode D2 and the first terminal of power transistor Q1; the second terminal of power device Q3 is connected to both the first terminal of coupling inductor L3 and the cathode of diode D3; the second terminal of coupling inductor L3 is connected to the anode of diode D1, and the third terminal of coupling inductor L3 is connected to both the first terminal of power device Q4 and the anode of diode D2; the cathode of diode D1 is connected to one end of inductor L2, and the other end of inductor L2 is connected to the first terminal of power transistor Q2; the second terminal of power device Q4 is connected to both the anode of diode D3 and the negative terminal of the power supply.

[0034] For the BUCK switching converter, although its power transistor Q2 is a zero-voltage switch before and after turn-on due to the early freewheeling turn-on and delayed turn-off of its anti-parallel diode (body diode), its anti-parallel diode is still hard-turned off, resulting in huge reverse recovery losses. In addition, for its power transistor Q1, since the voltage across the power transistor Q1 is the input voltage Vin before and after turn-on, both turn-on and turn-off are hard switches, resulting in huge switching losses.

[0035] This embodiment adds a soft-switching auxiliary circuit to the original BUCK switch converter. The soft-switching auxiliary circuit includes power devices Q3 and Q4, coupling inductors L3 and L2, diodes D1, D2 and D3.

[0036] The principle of the soft-switching auxiliary circuit is as follows: After power transistor Q2 is turned off and before power transistor Q1 is turned on, the source voltage of power transistor Q1 is charged to near Vin, and then power transistor Q1 is turned on. At this time, since the drain voltage of power transistor Q1 is Vin, power transistor Q1 is turned on with zero voltage. When power transistor Q1 is turned off, since the parasitic capacitances of power transistor Q1 and power transistor Q2 both have a voltage holding function, by appropriately selecting the values ​​of the parasitic capacitances of power transistor Q1 and power transistor Q2, zero-voltage turn-off of power transistor Q1 can be achieved. In addition, for power transistor Q2, due to the effect of the soft-switching auxiliary circuit, the voltage across its terminals only begins to rise after the current flowing through the anti-parallel diode of power transistor Q2 is zero, thus there is no reverse recovery loss. By adding diodes D2 and D3 to the soft-switching auxiliary circuit, the coupled inductor L3 can effectively reset the magnetic flux, ensuring that the semiconductor devices in the soft-switching auxiliary circuit achieve the soft-switching effect without stress spikes across the entire load range and input voltage range. The role of diode D1 is to ensure that the inductor L2 will not be reverse-magnetized after the current resonates to 0, making the control of the auxiliary soft-switching circuit simpler.

[0037] Specifically, the coupling inductor L3 includes a first inductor and a second inductor. The first end is the opposite-named end of the first inductor, the second end is the node connecting the same-named end of the first inductor and the opposite-named end of the second inductor, and the third end is the same-named end of the second inductor. The number of turns of the first inductor and the second inductor are equal.

[0038] Specifically, power device Q3 is a MOSFET, IGBT, or diode. When power device Q3 is a MOSFET or IGBT, the first terminal of power device Q3 is the drain and the second terminal is the source. When power device Q3 is a diode, the first terminal of power device Q3 is the cathode and the second terminal is the anode.

[0039] Power device Q4 can be a MOSFET, IGBT, or diode. When power device Q4 is a MOSFET or IGBT, the first terminal of power device Q4 is the drain and the second terminal is the source. When power device Q4 is a diode, the first terminal of power device Q4 is the cathode and the second terminal is the anode.

[0040] Both power transistors Q1 and Q2 are either MOSFETs or IGBTs. The first terminal of both power transistors Q1 and Q2 is the drain, and the second terminal is the source.

[0041] In the specific implementation process, power transistors Q1, Q2, Q3, and Q4 are all MOSFETs.

[0042] Figure 5 This is the control timing and waveform of the switching converter according to the first embodiment of the present invention. Now, in conjunction with... Figure 5 The six stages described for each cycle (from time t0 to time t6, denoted as T) are explained in detail below:

[0043] During the T0-T1 phase: At the initial time T0, power device Q3 is turned on, and the current flowing through inductor L2 begins to increase until time T1, when the current in inductor L2 is the same as the current in inductor L1. During this period, the current flowing through inductor L2 is divided into two parts. The first part flows out from the positive terminal of the input power supply Vin, passes through power device Q3, flows into the first terminal of coupling inductor L3, flows out from the second terminal, and then passes through diode D1, inductor L2, inductor L1, and capacitor C1 to the negative terminal of the input power supply. The second part flows out from one end of inductor L1, passes through capacitor C1 and power device Q4, flows into the third terminal of coupling inductor L3, flows out from the second terminal, and then passes through diode D1 and inductor L2 to the other end of inductor L1. Because coupling inductors L3 and L2 exist in the current loop when power devices Q3 and Q4 are turned on, and because the inductor current cannot change abruptly, zero-current turn-on of power devices Q3 and Q4 can be achieved.

[0044] T1-T2 Stage: In stage T1, since the current flowing through inductors L2 and L3 is the same, the drain voltage of power transistor Q2 will begin to rise as the current in inductor L2 continues to increase. Because the turns ratio of coupling inductor L3 is 1:1, when the drain voltage of power transistor Q2 rises to 1 / 2 Vin, the current flowing through inductor L2 reaches its maximum value. Afterward, the current flowing through inductor L2 begins to decrease, and the drain voltage of power transistor Q2 continues to rise. When the drain voltage of power transistor Q2 rises to Vin, the current flowing through inductor L2 decreases to be the same as the current in inductor L3. Since power transistor Q1 turns on when the drain voltage of power transistor Q2 rises to Vin at time T2, zero-voltage turn-on is achieved. Because the body diode of power transistor Q2 will engage and remain on when power transistor Q2 is turned off, power transistor Q2 achieves zero-voltage turn-off.

[0045] During the T2-T3 phase: the current flowing through inductor L2 continues to decrease until time T3, when the current in inductor L2 drops to 0. At this point, power devices Q3 and Q4 are turned off, achieving zero-current turn-off. Since it is difficult to precisely achieve the point where the current in inductor L2 drops to 0 before power devices Q3 and Q4 turn off in actual control, a demagnetizing circuit, including diodes D2 and D3, is added to the coupled inductor L3 to prevent inductor saturation without affecting the system control logic. After power devices Q3 and Q4 are turned off, the current flowing through the coupled inductor L3 is demagnetized by diodes D2 and D3, ensuring the magnetic balance of the coupled inductor within one cycle and preventing saturation.

[0046] During the T3-T4 phase: Power transistor Q1 remains on until time T4, when it turns off. Because the parasitic capacitances of power transistors Q1 and Q2 maintain voltage, zero-voltage turn-off of power transistor Q1 can be achieved.

[0047] T4-T5 stage: After power transistor Q1 is turned off, the drain voltage of power transistor Q2 begins to decrease. When the drain voltage of power transistor Q2 drops to 0, power transistor Q2 begins to turn on, achieving zero-voltage turn-on of power transistor Q2.

[0048] T4-T5 stage: Power transistor Q2 remains on until the next stage.

[0049] Thus, one cycle of the first embodiment of the present invention has ended.

[0050] Second Embodiment

[0051] Unlike the first embodiment, in this embodiment, the main circuit is a BOOST converter, such as... Figure 6The diagram shown is a schematic of the switching converter in this embodiment. In this embodiment, a soft-switching converter is provided, including a main circuit. The main circuit includes a power transistor Q1, a power transistor Q2, an inductor L1, and a capacitor C1. The first end of the power transistor Q1 is connected to one end of the capacitor C1, and the second end of the power transistor Q1 is connected to one end of the inductor L1 and the first end of the power transistor Q2. The other end of the inductor L1 is used to connect to the positive terminal of the power supply, and the second end of the power transistor Q2 is connected to the other end of the capacitor C1 and is used to connect to the negative terminal of the power supply.

[0052] It also includes a soft-switching auxiliary circuit, which includes power device Q3, power device Q4, diodes D1, D2, and D3, inductor L2, and coupling inductor L3; the first terminal of power device Q3 is connected to both the cathode of diode D2 and the first terminal of power transistor Q1; the second terminal of power device Q3 is connected to both the first terminal of coupling inductor L3 and the cathode of diode D3; the second terminal of coupling inductor L3 is connected to the cathode of diode D1, and the third terminal of coupling inductor L3 is connected to both the first terminal of power device Q4 and the anode of diode D2; the anode of diode D1 is connected to one end of inductor L2, and the other end of inductor L2 is connected to the first terminal of power transistor Q2; the second terminal of power device Q4 is connected to both the anode of diode D3 and the negative terminal of the power supply.

[0053] For the BOOST switching converter, although its power transistor Q1 is a zero-voltage switch before and after turn-on due to the early freewheeling turn-on and delayed turn-off of its anti-parallel diode, the anti-parallel diode is still hard-turned off, resulting in huge reverse recovery losses. Furthermore, for its power transistor Q2, since the voltage across Q1 is the output voltage Vo before and after turn-on, both turn-on and turn-off are hard switching, resulting in huge switching losses.

[0054] By adding a soft-switching auxiliary circuit to the original BOOST switching converter, the soft-switching auxiliary circuit includes power devices Q3 and Q4, coupling inductors L3 and L2, diodes D1, D2 and D3.

[0055] The principle of the soft-switching auxiliary circuit is as follows: After power transistor Q1 is turned off and before power transistor Q2 is turned on, the drain voltage of power transistor Q2 is pulled down to near 0V before power transistor Q2 is turned on. At this time, since the source voltage of power transistor Q2 is 0V, power transistor Q2 is turned on with zero voltage. When power transistor Q2 is turned off, since the parasitic capacitances of power transistors Q1 and Q2 both have a voltage holding function, by appropriately selecting the values ​​of the parasitic capacitances of power transistors Q1 and Q2, zero-voltage turn-off of power transistor Q2 can be achieved. In addition, for power transistor Q1, due to the effect of the soft-switching auxiliary circuit, the voltage across its terminals only begins to rise after the current flowing through the anti-parallel diode of power transistor Q1 is zero, thus there is no reverse recovery loss. By adding diodes D2 and D3 to the soft-switching auxiliary circuit, the coupling inductor L3 can effectively reset the magnetic flux, ensuring that the semiconductor devices in the soft-switching auxiliary circuit achieve the soft-switching effect without stress spikes across the entire load range and the entire input voltage range.

[0056] Specifically, the coupling inductor L3 includes a first inductor and a second inductor. The first end is the opposite-named end of the first inductor, the second end is the node connecting the same-named end of the first inductor and the opposite-named end of the second inductor, and the third end is the same-named end of the second inductor. The number of turns of the first inductor and the second inductor are equal.

[0057] Specifically, power device Q3 is a MOSFET, IGBT, or diode. When power device Q3 is a MOSFET or IGBT, the first terminal of power device Q3 is the drain and the second terminal is the source. When power device Q3 is a diode, the first terminal of power device Q3 is the cathode and the second terminal is the anode.

[0058] Power device Q4 can be a MOSFET, IGBT, or diode. When power device Q4 is a MOSFET or IGBT, the first terminal of power device Q4 is the drain and the second terminal is the source. When power device Q4 is a diode, the first terminal of power device Q4 is the cathode and the second terminal is the anode.

[0059] Both power transistors Q1 and Q2 are either MOSFETs or IGBTs. The first terminal of both power transistors Q1 and Q2 is the drain, and the second terminal is the source.

[0060] In the specific implementation process, power transistors Q1, Q2, Q3, and Q4 are all MOSFETs.

[0061] Figure 7 The control timing and waveforms of the switching converter in this embodiment are now presented in conjunction with... Figure 7 The six stages described for each cycle (from time t0 to time t6, denoted as T) are explained in detail below:

[0062] During the T0-T1 phase: At the initial time T0, power device Q4 is turned on, and the current flowing through inductor L2 begins to increase until time T1, when the current in inductor L2 is the same as the current in inductor L1. During this period, the current flowing through inductor L2 is divided into two parts. The first part flows from the drain of power transistor Q2 through inductor L2 and diode D1, then into the second terminal of coupling inductor L3 and out the third terminal, passing through power device Q4 to the source of power transistor Q2. The second part flows from the drain of power transistor Q2 through inductor L2 and diode D1, then into the second terminal of coupling inductor L3 and out the first terminal, passing through power device Q3 and capacitor C1 to the source of power transistor Q2. Because coupling inductors L3 and L2 exist in the current loop when power devices Q4 and Q3 are turned on, and because the inductor current cannot change abruptly, zero-current turn-on of power devices Q4 and Q3 can be achieved.

[0063] During the T1-T2 phase: the equivalent parallel capacitance of the drain and source of power transistor Q2 is relatively small, so the current flowing through inductors L2 and L3 is approximately the same. At this time, the drain voltage of power transistor Q2 begins to decrease until it reaches 0, at which point Q2 turns on again, thus achieving zero-voltage turn-on. Since the body diode of power transistor Q1 remains on when Q1 is turned off, Q1 experiences zero-voltage turn-off.

[0064] During the T2-T3 phase: the current flowing through inductor L2 continues to decrease until time T3, when the current in inductor L2 drops to 0. At this point, power devices Q4 and Q3 are turned off, achieving zero-current turn-off. Since it is difficult to precisely achieve the point where the current in inductor L2 drops to 0 before power devices Q4 and Q3 turn off in actual control, a demagnetizing circuit, including diodes D2 and D3, is added to the coupled inductor L3 to prevent inductor saturation without affecting the system control logic. After power devices Q4 and Q3 are turned off, the current flowing through the coupled inductor L3 is demagnetized by diodes D2 and D3, ensuring the magnetic balance of the coupled inductor within one cycle and preventing saturation.

[0065] During the T3-T4 phase: Power transistor Q2 remains on until time T4, when it turns off. Because the parasitic capacitances of power transistors Q1 and Q2 maintain voltage, zero-voltage turn-off of power transistor Q2 can be achieved.

[0066] T4-T5 stage: After power transistor Q2 is turned off, the drain voltage of power transistor Q2 begins to rise. When the drain voltage of Q2 rises to Vin, power transistor Q1 begins to turn on, realizing zero-voltage turn-on of power transistor Q1.

[0067] T4-T5 stage: Power transistor Q1 remains on until the next stage.

[0068] Thus, one cycle of the second embodiment of the present invention has ended.

[0069] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A soft-switching converter, comprising a main circuit, the main circuit including a power transistor Q1, a power transistor Q2, an inductor L1, and a capacitor C1; a first terminal of the power transistor Q1 is connected to the positive terminal of a power supply, a second terminal of the power transistor Q1 is connected to both one end of the inductor L1 and the first terminal of the power transistor Q2, the other end of the inductor L1 is connected to one end of the capacitor C1, and the second terminal of the power transistor Q2 is connected to both the other end of the capacitor C1 and is used to connect to the negative terminal of the power supply; characterized in that... : It also includes a soft-switching auxiliary circuit, which comprises power device Q3, power device Q4, diodes D1, D2, and D3, inductor L2, and coupling inductor L3. The first terminal of power device Q3 is simultaneously connected to the cathode of diode D2 and the first terminal of power transistor Q1. The second terminal of power device Q3 is simultaneously connected to the first terminal of coupling inductor L3 and the cathode of diode D3. The second terminal of coupling inductor L3 is connected to the anode of diode D1, and the third terminal of coupling inductor L3 is simultaneously connected to the first terminal of power device Q4 and the anode of diode D2. The cathode of diode D1 is connected to one end of inductor L2, and the other end of inductor L2 is connected to the first terminal of power transistor Q2. The second terminal of power device Q4 is simultaneously connected to the anode of diode D3 and the negative terminal of the power supply. The coupled inductor L3 includes a first inductor and a second inductor. The first end is the opposite-named end of the first inductor, the second end is the node connecting the same-named end of the first inductor and the opposite-named end of the second inductor, and the third end is the same-named end of the second inductor. The drive signal connected to the control terminal of power device Q4 is the same as the drive signal connected to the control terminal of power device Q3.

2. The soft-switching converter according to claim 1, characterized in that, The first inductor and the second inductor have the same number of turns.

3. The soft-switching converter according to claim 1, characterized in that, Power device Q3 can be a MOSFET, an IGBT, or a diode. When power device Q3 is a MOSFET, its first terminal is the drain and its second terminal is the source. When power device Q3 is an IGBT, its first terminal is the collector and its second terminal is the emitter. When power device Q3 is a diode, its first terminal is the cathode and its second terminal is the anode.

4. The soft-switching converter according to claim 1, characterized in that, Power device Q4 can be a MOSFET, an IGBT, or a diode. When power device Q4 is a MOSFET, its first terminal is the drain and its second terminal is the source. When power device Q4 is an IGBT, its first terminal is the collector and its second terminal is the emitter. When power device Q4 is a diode, its first terminal is the cathode and its second terminal is the anode.

5. The soft-switching converter according to any one of claims 1-4, characterized in that, Power transistors Q1 and Q2 are both MOSFETs or IGBTs. When power transistors Q1 and Q2 are MOSFETs, their first terminals are both drains and their second terminals are both sources. When power transistors Q1 and Q2 are IGBTs, their first terminals are both collectors and their second terminals are both emitters.

6. The soft-switching converter according to claim 5, characterized in that, Power transistors Q1 and Q2 are driven by complementary transistors with dead time; the turn-on time of power device Q3 is later than the turn-on time of power transistor Q2, and the turn-off time of power device Q3 is later than the turn-on time of power transistor Q1 and the turn-off time of power transistor Q2.

7. A soft-switching converter, comprising a main circuit, the main circuit including a power transistor Q1, a power transistor Q2, an inductor L1, and a capacitor C1; a first terminal of the power transistor Q1 is connected to a first terminal of the capacitor C1, a second terminal of the power transistor Q1 is connected to both a first terminal of the inductor L1 and a first terminal of the power transistor Q2, the other terminal of the inductor L1 is connected to the positive terminal of a power supply, and the second terminal of the power transistor Q2 is connected to both a second terminal of the capacitor C1 and a negative terminal of the power supply; characterized in that... : It also includes a soft-switching auxiliary circuit, which comprises power device Q3, power device Q4, diodes D1, D2, and D3, inductor L2, and coupling inductor L3. The first terminal of power device Q3 is simultaneously connected to the cathode of diode D2 and the first terminal of power transistor Q1. The second terminal of power device Q3 is simultaneously connected to the first terminal of coupling inductor L3 and the cathode of diode D3. The second terminal of coupling inductor L3 is connected to the cathode of diode D1, and the third terminal of coupling inductor L3 is simultaneously connected to the first terminal of power device Q4 and the anode of diode D2. The anode of diode D1 is connected to one end of inductor L2, and the other end of inductor L2 is connected to the first terminal of power transistor Q2. The second terminal of power device Q4 is simultaneously connected to the anode of diode D3 and the negative terminal of the power supply. The coupled inductor L3 includes a first inductor and a second inductor. The first end is the opposite-named end of the first inductor, the second end is the node connecting the same-named end of the first inductor and the opposite-named end of the second inductor, and the third end is the same-named end of the second inductor. The drive signal connected to the control terminal of power device Q4 is the same as the drive signal connected to the control terminal of power device Q3.

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