Control circuit and switching converter applying the same

Abstract

The application discloses a control circuit and a switching converter applying the same. The technical scheme of the embodiment of the application controls the auxiliary switch tube to be turned on for a predetermined time period before the main switch tube is turned on, and adjusts the turn-on time of the auxiliary switch tube according to the input voltage and output voltage information of the switching converter, so that the main switch tube is discharged by a discharge current before being turned on to realize zero-voltage turn-on and effectively reduce turn-on loss.

Description

Technical Field

[0001] This invention relates to power electronics technology, specifically to switching converters and their control circuits. Background Technology

[0002] A switching converter stores energy in a magnetic component when the main power transistor is on and delivers this stored energy to the load when the transistor is off. When the main power transistor is off, resonance occurs between the magnetic component and the junction capacitance of the transistor, resulting in conduction losses when the transistor turns back on, leading to low power conversion efficiency. To reduce these conduction losses, existing technologies employ a quasi-resonant method to control the transistor's turn-on, achieving zero-voltage turn-on when the drain-source voltage drops to its minimum. However, when the input voltage of the switching converter changes, it becomes difficult for the transistor to achieve zero-voltage turn-on, increasing turn-on losses and reducing system efficiency. Summary of the Invention

[0003] In view of this, embodiments of the present invention provide a switching converter and its control circuit, which effectively reduces the turn-on loss of the main switching transistor and improves system efficiency by controlling the auxiliary switching transistor to be turned on for a predetermined period of time before the main power transistor is turned on.

[0004] According to a first aspect of the present invention, a control circuit for a switching converter is provided, the switching converter including a main switching transistor and an auxiliary switching transistor, the control circuit including:

[0005] A zero-voltage controller is configured to generate an auxiliary switching transistor control signal based on the input and output voltage information of the switching converter, to control the auxiliary switching transistor to conduct for a first time period; and

[0006] The primary controller is configured to generate a primary control signal to control the main switch to conduct for a second time period.

[0007] Preferably, the reference ground potential of the zero-voltage controller is coupled to the common terminal of the magnetic element of the switching converter and the main switch, and the reference ground potential of the primary-side controller is coupled to the reference ground potential of the switching converter.

[0008] Preferably, the reference ground potential of the zero-voltage controller is the same as the reference ground potential of the primary-side controller.

[0009] Preferably, the zero-voltage controller is integrated into the first control chip to generate the auxiliary control signal, and the primary-side controller is integrated into the second control chip to generate the primary control signal.

[0010] Preferably, the length of the first time period is controlled within a preset range so that the drain-source voltage of the main switch drops to zero after the first time period ends and before the second time period begins.

[0011] Preferably, the drain-source voltage of the main switch has at least one valley before the auxiliary switch is turned on.

[0012] Preferably, the length of the first time period has the same trend of change as the input voltage of the switching converter and the opposite trend of change as the output voltage of the switching converter.

[0013] Preferably, the zero-voltage controller includes:

[0014] The input terminal is configured to receive the input voltage of the switching converter;

[0015] The output terminal is configured to generate the auxiliary tube control signal; and

[0016] The reference terminal is coupled to the common terminal of the magnetic element of the switching converter and the main switching transistor.

[0017] Preferably, the zero-voltage controller includes:

[0018] The input terminal is coupled to the common terminal of the magnetic element of the switching converter and the main switching transistor;

[0019] The output terminal is configured to generate the auxiliary tube control signal; and

[0020] The reference terminal is coupled to the reference ground potential of the switching converter.

[0021] Preferably, within one switching cycle, the zero-voltage controller is configured to sample the voltage at the common terminal of the magnetic element and the main switching transistor to generate a first voltage, sample the maximum value of the voltage at the common terminal of the magnetic element and the main switching transistor to generate a second voltage, and subtract the second voltage from the first voltage to generate a third voltage, wherein the first voltage characterizes the input voltage of the switching converter, and the third voltage characterizes the output voltage of the switching converter.

[0022] Preferably, the switching converter includes a transformer, the transformer including a primary winding and an auxiliary winding, and the zero-voltage controller includes:

[0023] The input terminal is coupled to the common terminal of the auxiliary winding and the auxiliary switching transistor;

[0024] The output terminal is configured to generate the auxiliary tube control signal; and

[0025] The reference terminal is coupled to the reference ground potential of the switching converter.

[0026] Preferably, within a switching cycle, the zero-voltage controller is configured to sample the voltage at the common terminal of the auxiliary winding and the auxiliary switching transistor to generate a fourth voltage, sample the maximum value of the voltage at the common terminal of the auxiliary winding and the auxiliary switching transistor to generate a fifth voltage, and subtract the fifth voltage from the fourth voltage to generate a sixth voltage, wherein the fourth voltage characterizes the output voltage of the switching converter and the sixth voltage characterizes the input voltage of the switching converter.

[0027] Preferably, the switching converter operates in discontinuous current mode.

[0028] According to a second aspect of the present invention, a switching converter is provided. The switching converter includes: any of the control circuits described in the first aspect;

[0029] The power stage circuit includes the main switching transistor and magnetic components; and

[0030] Clamping circuit, including auxiliary switching transistor.

[0031] Preferably, the clamping circuit is connected in series with the main switching transistor and includes an auxiliary switching transistor and a clamping capacitor connected between the input terminal of the switching converter and the main switching transistor.

[0032] Preferably, the clamping circuit is connected in parallel with the main switch and includes an auxiliary switch and a clamping capacitor connected in series between the first and second ends of the main switch.

[0033] Preferably, the magnetic element is a transformer, which includes a primary winding, at least one secondary winding, and an auxiliary winding. The clamping circuit is connected in parallel across the two ends of the auxiliary winding and includes an auxiliary switching transistor and a clamping capacitor connected in series between the first and second ends of the auxiliary winding.

[0034] The technical solution of this invention controls the auxiliary switch to be turned on for a predetermined period of time before the main power transistor is turned on, so that the main switch discharges its parasitic capacitance through a discharge current before being turned on, thereby achieving zero-voltage turn-on, effectively reducing turn-on losses and improving system efficiency. Attached Figure Description

[0035] The above and other objects, features and advantages of the present invention will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0036] Figure 1 This is a circuit diagram of the switching converter according to the first embodiment of the present invention;

[0037] Figure 2 This is a circuit diagram of the switching converter according to the second embodiment of the present invention;

[0038] Figure 3 This is a circuit diagram of the switching converter according to the third embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the zero-voltage controller according to an embodiment of the present invention;

[0040] Figure 5 This is a waveform diagram of the switching converter in an embodiment of the present invention. Detailed Implementation

[0041] The present invention is described below based on embodiments, but the invention is not limited to these embodiments. In the detailed description of the invention below, certain specific details are described in detail. Those skilled in the art will fully understand the invention even without these details. To avoid obscuring the essence of the invention, well-known methods, processes, flows, elements, and circuits are not described in detail.

[0042] Furthermore, those skilled in the art should understand that the accompanying drawings provided herein are for illustrative purposes only and are not necessarily drawn to scale.

[0043] Furthermore, it should be understood that in the following description, "circuit" refers to a conductive loop consisting of at least one element or sub-circuit connected by electrical or electromagnetic connections. When an element or circuit is said to be "connected" to another element or "connected" between two nodes, it can be directly coupled or connected to another element, or there may be intermediate elements. The connection between elements can be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly coupled to" or "directly connected" to another element, it means that there are no intermediate elements between them.

[0044] Unless the context explicitly requires it, the words "comprising," "including," and similar terms throughout the specification and claims should be interpreted as encompassing rather than being exclusive or exhaustive; that is, meaning "including but not limited to."

[0045] In the description of this invention, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0046] Figure 1This is a circuit diagram of a switching converter according to a first embodiment of the present invention. The switching converter in this embodiment is a flyback switching converter, including a power stage circuit, a clamping circuit 1, and a control circuit 10. The control circuit 10 includes a zero-voltage controller 100 and a primary-side controller 101. The power stage circuit includes a transformer T, a main switching transistor Sm connected in series with the primary winding of the transformer T, and a freewheeling transistor SR and an output capacitor Co connected in series with the secondary winding of the transformer T. Figure 1 As shown, the first terminal (e.g., the opposite-name terminal) of the primary winding of transformer T receives the input voltage Vin, and the second terminal (e.g., the same-name terminal) of the primary winding of transformer T is connected to the first terminal of the main switch Sm. The second terminal of the main switch Sm is coupled to the primary reference ground. The first terminal (e.g., the same-name terminal) of the secondary winding of transformer T is connected to the first terminal of the freewheeling diode SR. The output capacitor Co is connected between the second terminal of the freewheeling diode SR and the second terminal (e.g., the opposite-name terminal) of the secondary winding of transformer T. A DC output voltage Vout is provided across the output capacitor Co. The clamping circuit 1 is connected in series with the main switch Sm of transformer T and includes an auxiliary switch Sa and a clamping capacitor Cc connected in series with the main switch Sm. By providing an active clamping circuit, the withstand voltage of the switch can be reduced, the ZVS range can be expanded, and thus the switching converter can be applied to a wide input voltage range. In this embodiment, the flyback switching converter also includes a secondary controller 103 for controlling the freewheeling diode SR. It should be understood that in the embodiments of the present invention, the freewheeling diode can be replaced by a diode, or other electronically controlled switches can be used to achieve the above functions. Figure 1 In the diagram, the primary winding of transformer T can be equivalent to a series magnetizing inductance Lm and leakage inductance Lk, both shown as dashed lines. Depending on the implementation, the input voltage Vin can be an unrectified AC input voltage, such as 220V AC, or a DC input voltage. The zero-voltage controller 100 is configured to generate an auxiliary transistor control signal V based on the input and output voltage information of the switching converter. Sa During the first time period when the auxiliary switch Sa is turned on, the primary-side controller 101 is configured to generate the primary control signal V. Sm The main switch Sm is controlled to conduct for a second time period. In this embodiment, the reference ground of the zero-voltage controller 100 is the common terminal of the primary winding and the main switch Sm, and the reference ground of the primary controller 101 is the reference ground of the switching converter.

[0047] In this embodiment, the length of the first time period is within a preset range so that the drain-source voltage of the main switch Sm drops to zero after the end of the first time period and before the start of the second time period. Furthermore, the drain-source voltage of the main switch Sm has at least one valley before the auxiliary switch Sa is turned on. For example, if the switching converter operates in quasi-resonant mode, the zero-voltage controller 100 controls the auxiliary switch Sa to start turning on by detecting the number of valleys in the drain-source voltage of the main switch Sm, and turns on the auxiliary switch Sa for the first time period.

[0048] In this embodiment, before the main switch Sm is turned on, the zero-voltage controller 100 controls the auxiliary switch Sa to conduct for a predetermined period of time, causing the clamping circuit to start working. During the conduction of the auxiliary switch Sa, the clamping capacitor Cc provides reverse excitation to the primary winding Lm. After the excitation ends, the primary winding Lm continues to flow through the parasitic capacitance of the main switch Sm until the voltage on the parasitic capacitance of the main switch Sm is released. At the same time, the negative current flowing through the primary winding Lm drops to zero. At this time, the primary controller 102 controls the main switch Sm to conduct, and the main switch Sm achieves zero-voltage turn-on, thereby recovering energy in the leakage inductance Lk to improve electromagnetic interference (EMI) and reducing the voltage at the two power terminals of the main switch Sm when it is turned on, so as to reduce turn-on losses.

[0049] In this embodiment, the zero-voltage controller 100 is integrated into the first control chip to generate the auxiliary transistor control signal V. Sa The primary-side controller 101 is integrated into the second control chip to generate the primary control signal V. Sm The reference ground potential of the first control chip is the common terminal of the primary winding and the main switch Sm, and the reference ground potential of the second control chip is the reference ground of the switching converter.

[0050] In a preferred embodiment, the zero-voltage controller 100 samples the input voltage Vin and output voltage Vout of the switching converter, and adjusts the on-time of the auxiliary switch Sa based on the input and output voltage information to control the on-time of the auxiliary switch Sa within a preset range. This causes the drain-source voltage of the main switch Sm to drop to zero after the auxiliary switch Sa is turned off and before the main switch Sm is turned on. Furthermore, the on-time of the auxiliary switch Sa has the same trend as the input voltage Vin and the opposite trend to the output voltage Vout.

[0051] Furthermore, the zero-voltage controller 100 has an input terminal for receiving a sampling signal Vs (input voltage Vin) to obtain input voltage and output voltage information; a reference terminal connected to the common terminal of the primary winding and the main switching transistor Sm, which is the reference ground potential of the zero-voltage controller 100; and an output terminal for generating an auxiliary transistor control signal V. Sa The auxiliary switch Sa is controlled to turn on or off. In this embodiment, the zero-voltage controller 100 can directly sample the input voltage Vin to obtain input voltage information. Since the reference ground potential of the zero-voltage controller 100 is the common terminal of the primary winding and the main switch Sm, the zero-voltage controller 100 can obtain the voltage on the primary winding by sampling the input voltage Vin, and thus obtain the output voltage information based on the voltage on the primary winding.

[0052] Furthermore, the zero-voltage controller 100 controls the on-time of the auxiliary switch Sa to be within a preset range so that the drain-source voltage of the main switch Sm drops to zero after the auxiliary switch Sa is turned off and before the main switch Sm is turned on.

[0053] In this embodiment, the switching converter operates in discontinuous current mode, and the zero-voltage controller 100 controls the auxiliary switching transistor Sa to conduct for a predetermined period of time before the main switching transistor Sm is turned on, so as to achieve zero-voltage turn-on.

[0054] In this application, the switching transistor is a transistor that operates in switching mode to provide a current path, including a bipolar transistor or a field-effect transistor. The first terminal and the second terminal of the switching transistor are respectively the high potential terminal and the low potential terminal on the current path, and the control terminal is used to receive a control signal to control the switching transistor to turn on and off.

[0055] Unlike the control methods of existing switching converters, the switching converter in this embodiment controls the auxiliary switching transistor Sa to conduct for a predetermined period of time before the main switching transistor Sm is turned on. At the same time, the conduction time of the auxiliary switching transistor Sa is adjusted according to the input voltage and output voltage information of the switching converter, so that the main switching transistor discharges its parasitic capacitance through a discharge current before it is turned on, thereby achieving zero-voltage turn-on and effectively reducing turn-on losses.

[0056] Figure 2 This is a circuit diagram of a switching converter according to a second embodiment of the present invention. Figure 2As shown, the switching converter in this embodiment of the invention is a flyback switching converter, including a power stage circuit, a clamping circuit 1, and a control circuit. The control circuit includes a zero-voltage controller 100 and a primary-side controller 101. The power stage circuit, primary-side controller 101, secondary-side controller 103, and control method of this switching converter are basically the same as those of the switching converter in the first embodiment, and will not be described in detail here. The difference is that the clamping circuit 1 is connected in parallel with the main switching transistor Sm, and includes an auxiliary switching transistor Sa and a clamping capacitor Cc connected in series between the first and second terminals of the main switching transistor Sm. In this embodiment, the reference ground potentials of the zero-voltage controller 100 and the primary-side controller 101 are the same.

[0057] In this embodiment, the zero-voltage controller 100 includes an input terminal connected to the common terminal of the primary winding and the main switching transistor Sm, used to sample the input and output voltage information of the switching converter; and an output terminal used to generate the auxiliary transistor control signal V. Sa It controls the auxiliary switch Sa to turn on or off; and the reference terminal is connected to the reference ground of the switching converter.

[0058] In a preferred embodiment, based on the volt-second balance principle of the primary winding, the zero-voltage controller 100 generates a first voltage within one switching cycle by sampling and holding the voltage at the common terminal of the primary winding and the main switch Sm, wherein the first voltage represents the input voltage information. The zero-voltage controller 100 generates a second voltage within one switching cycle by sampling and holding the maximum value of the voltage at the common terminal of the primary winding and the main switch Sm, and then subtracts the second voltage from the first voltage to generate a third voltage, wherein the third voltage represents the output voltage information.

[0059] Figure 3 This is a circuit diagram of a switching converter according to the third embodiment of the present invention. Figure 3 As shown, the switching converter in this embodiment of the invention is a flyback switching converter, including a power stage circuit, a clamping circuit 1, and a control circuit. The control circuit includes a zero-voltage controller 100 and a primary-side controller 101. In this embodiment, the transformer includes an auxiliary winding. The auxiliary winding is coupled to the primary winding of the transformer. The power stage circuit, primary-side controller 101, secondary-side controller 103, and control method of this switching converter are basically the same as those of the switching converter in the first embodiment, and will not be described in detail here. The difference is that the clamping circuit 1 is connected in parallel across the two ends of the auxiliary winding, and includes an auxiliary switching transistor Sa and a clamping capacitor Cc connected in series between the first and second ends of the auxiliary winding. In this embodiment, the reference ground potentials of the zero-voltage controller 100 and the primary-side controller 101 are the same.

[0060] In this embodiment, the zero-voltage controller 100 includes an input terminal connected to the common terminal of the auxiliary winding and the auxiliary switching transistor Sa, used to sample the input voltage and output voltage information of the switching converter; and an output terminal used to generate the auxiliary transistor drive signal V. Sa It controls the auxiliary switch Sa to turn on or off; and the reference terminal is connected to the primary side reference ground of the switching converter.

[0061] In a preferred embodiment, due to the coupling between the auxiliary winding and the primary winding, the zero-voltage controller 100 generates a fourth voltage within one switching cycle by sampling and holding the voltage at the common terminal of the auxiliary winding and the auxiliary switch Sa, wherein the fourth voltage represents the output voltage information. The zero-voltage controller 100 generates a fifth voltage within one switching cycle by sampling and holding the maximum value of the voltage at the common terminal of the auxiliary winding and the auxiliary switch Sa, and subtracts the fifth voltage from the fourth voltage to generate a sixth voltage, wherein the sixth voltage represents the input voltage information.

[0062] It should be understood that in the above embodiments, since the connection method of the clamping circuit 1 in the switching converter changes, the sampling point of the zero-voltage controller needs to be adaptively adjusted accordingly. Furthermore, the switching converter in the embodiments of the present invention can also be a Buck converter, a Boost converter, or other switching converters, and is not limited to the flyback switching converters listed. In the above embodiments, the magnetic components are all transformers; in other embodiments, the magnetic components can be inductors or other similar components.

[0063] Figure 4 This is a schematic diagram of the zero-voltage controller according to an embodiment of the present invention. The zero-voltage controller 100 includes a detection circuit 41 and a control signal generation circuit 42. The detection circuit 41 is configured to receive a sampling signal Vs to generate an input sampling signal SVin representing input voltage information and an output sampling signal SVout representing output voltage information. The control signal generation circuit 42 is configured to generate an auxiliary tube control signal V based on the input sampling signal SVin and the output sampling signal SVout. Sa The on-time of the auxiliary switch Sa is adjusted so that the main switch discharges its parasitic capacitance through a discharge current before turning on, thereby achieving zero-voltage turn-on and effectively reducing turn-on losses. The zero-voltage controller 100 adjusts the on-time of the auxiliary switch Sa based on the input sampling signal SVin and the output sampling signal SVout, i.e., the auxiliary switch control signal V. Sa The effective length. In the auxiliary pipe control signal V... Sa When effective, the zero-voltage controller 100 controls the auxiliary switch Sa to conduct.

[0064] In a preferred embodiment, the flyback converter operates in discontinuous current mode (DCM) and employs quasi-resonant (QR) control. The zero-voltage controller 100 generates a trough detection signal Vring based on the sampled signal Vs to control the auxiliary switch Sa to turn on when the drain-source voltage of the main switch drops to a trough, thereby reducing the switching losses of the auxiliary switch Sa and improving the efficiency of the flyback converter. In this embodiment, the drain-source voltage of the main switch has at least one trough before the auxiliary switch Sa turns on. Figure 1 Taking a flyback converter as an example, the detection circuit 41 can obtain the trough detection signal Vring based on the sampled signal Vs, i.e., the input voltage Vin. The control signal generation circuit 42 generates an effective auxiliary tube control signal V based on the trough detection signal Vring. Sa To control the conduction of the auxiliary switch tube Sa.

[0065] The control signal generation circuit 42 sets the conduction time of the auxiliary switching transistor Sa within a preset range based on the input voltage Vin and output voltage Vout information, that is, the auxiliary transistor control signal V... Sa The effective length. For example, the conduction time of the auxiliary switch Sa can be set to be within a preset range (t0-th1, t0+th2), where th1 and th2 are time thresholds, which can be equal or unequal. The conduction time t0 can be set according to the type and working principle of the switching converter so that the conduction time of the auxiliary switch Sa is near time t0, thereby causing the drain-source voltage of the main switch Sm to drop to zero after the auxiliary switch Sa is turned off and before the main switch Sm is turned on.

[0066] Taking the flyback converter in this embodiment as an example, time t0 can be represented as follows:

[0067] (1)

[0068] Where K1 is a proportional parameter, which is related to the transformer's equivalent inductance, the junction capacitance between the freewheeling diode and the secondary reference ground, N is the transformer's turns ratio, SVin is the input sampling signal, and SVout is the output sampling signal.

[0069] In this embodiment, the conduction time of the auxiliary switch Sa (auxiliary switch control signal V) Sa The effective length can be directly set according to formula (1). The conduction time of the auxiliary switch tube Sa can be slightly less than or greater than time t0. Specifically, it can be adjusted according to the time thresholds th1 and th2.

[0070] Figure 5This is a waveform diagram of the switching converter in an embodiment of the present invention. This embodiment uses... Figure 1 Taking a flyback converter as an example, the drain voltage Vdrain of the main switch Sm and the voltage V on the primary winding are... bus-drain Supervisor control signal V Sm And auxiliary pipe control signal V Sa Shown sequentially from top to bottom. For example... Figure 5 As shown, at time t1, the supervisor control signal V Sm Effective, the main switch Sm changes from the off state to the on state, and the primary current I... P As the voltage gradually increases, the primary winding begins to store energy. At time t2, the main control signal V... Sm Invalid. The main switch Sm changes from the on state to the off state. The main switch Sm is turned off, and the primary current I... P As the voltage continues to decrease, the drain voltage Vdrain of the main switch Sm gradually increases relative to the input voltage Vin. At time t3, the voltage V on the primary winding... bus-drain A trough appears, meaning the drain-source voltage of the main switching transistor Sm is at a trough, and the auxiliary transistor control signal V... Sa Effective, auxiliary switch Sa is turned on. During the conduction period of auxiliary switch Sa, the primary current I... P The reverse increase accelerates the discharge speed of the junction capacitance of the main switch Sm, thereby reducing the resonance between the leakage inductance and the junction capacitance of the main switch Sm to zero (close to or approximately zero is considered to be zero resonance). At time t4, the auxiliary switch Sa is turned on for a predetermined period of time, and the auxiliary switch control signal V... Sa The auxiliary switch Sa turns off when the switch changes from active to inactive. At time t5, the primary current I... P When the voltage drops to zero, the drain voltage Vdrain of the main switch Sm resonates to zero, and the main control signal V... Sm Effective. The main switch Sm transitions from the off state to the on state, starting a new working cycle.

[0071] The technical solution of this invention controls the auxiliary switch Sa to conduct for a predetermined period of time before the main switch Sm is turned on. At the same time, the conduction time of the auxiliary switch Sa is adjusted according to the input voltage and output voltage information of the switching converter. This allows the main switch to discharge its parasitic capacitance through a discharge current before it is turned on, thereby achieving zero-voltage turn-on and effectively reducing turn-on losses.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can be modified and varied in various ways. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of protection of the present invention.

Claims

1. A control circuit for a switching converter, the switching converter comprising a main switching transistor and a clamping circuit connected in series with the main switching transistor, the clamping circuit comprising an auxiliary switching transistor and a clamping capacitor connected in series, characterized in that, The control circuit includes: A zero-voltage controller is configured to generate an auxiliary switching signal, control the auxiliary switching transistor to turn on by detecting the number of valleys in the drain-source voltage of the main switching transistor, and control the auxiliary switching transistor to turn on for a first time period based on the input and output voltage information of the switching converter, wherein the reference ground potential of the zero-voltage controller is connected to the magnetic element of the switching converter and the common terminal of the main switching transistor; and The primary-side controller is configured to generate a primary control signal to control the main switch to turn on when the negative current flowing through the magnetic element of the switching converter drops to zero, and to control the main switch to turn on for a second time period.

2. The control circuit according to claim 1, characterized in that, The reference ground potential of the primary-side controller is coupled to the reference ground potential of the switching converter.

3. The control circuit according to claim 1, characterized in that, The zero-voltage controller is integrated into the first control chip to generate the auxiliary control signal, and the primary-side controller is integrated into the second control chip to generate the primary control signal.

4. The control circuit according to claim 1, characterized in that, The length of the first time period is controlled within a preset range so that the drain-source voltage of the main switch drops to zero after the first time period ends and before the second time period begins.

5. The control circuit according to claim 1, characterized in that, Before the auxiliary switch is turned on, the drain-source voltage of the main switch has at least one valley.

6. The control circuit according to claim 1, characterized in that, The length of the first time period has the same trend as the input voltage of the switching converter and the opposite trend to the output voltage of the switching converter.

7. The control circuit according to claim 1, characterized in that, The zero-voltage controller is configured to sample the input voltage of the switching converter to generate an input sampling signal characterizing the input voltage information and an output sampling signal characterizing the output voltage information.

8. The control circuit according to claim 7, characterized in that, The zero-voltage controller includes: A detection circuit is configured to receive the input voltage of the switching converter and generate an input sampling signal characterizing the input voltage information, an output sampling signal characterizing the output voltage information, and a trough detection signal; and The control signal generation circuit is configured to control the auxiliary tube control signal to switch to an effective level according to the valley detection signal to control the auxiliary switch to start conducting, and to control the auxiliary switch to conduct for a first time period according to the input sampling signal and the output sampling signal.

9. The control circuit according to claim 1, characterized in that, The switching converter operates in discontinuous current mode.

10. A switching converter, comprising: Any one of the control circuits as described in claims 1-9; as well as Power stage circuit, including main switching transistor and magnetic components; as well as The clamping circuit includes an auxiliary switching transistor and a clamping capacitor connected in series, wherein the clamping circuit is connected in series with the main switching transistor.

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