Active clamp circuit, converter and power supply

Abstract

An active clamp circuit, comprising: a first energy storage element, a first branch and a second branch, wherein the first branch and the second branch are connected in parallel and are then connected to the first energy storage element in series; the first branch comprises a second energy storage element, and the second branch comprises an auxiliary switching transistor; when the clamp circuit is in a forward charging state, the first energy storage element and the first branch are turned on to form a clamp loop; the first energy storage element and the second energy storage circuit absorb leakage induction energy of a primary-side winding by means of the clamp loop; and when the clamp circuit is in a reverse excitation charging state for a transformer, the first energy storage element and the second branch are turned on to form a reverse excitation loop. In the present application, when the clamp circuit is subjected to forward charging, the voltage across two ends is the sum of the voltage of the first energy storage element and the voltage of the second energy storage element, and when the clamp circuit discharges, the voltage across the two ends is only the voltage of the first energy storage element, and thus when reverse excitation is performed on the transformer, the excitation voltage is less than a reflected voltage of a secondary-side winding, such that the secondary-side winding is not turned on, so as to eliminate the forward excitation of energy to a secondary side, thereby reducing the loss.

Description

Active clamp circuit, converter, and power supply

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on November 29, 2023, with application number 202311632526.7 and invention name “Active clamping circuit, converter and power supply”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of power electronics technology, and in particular to an active clamping circuit, a converter, and a power supply. Background Art

[0003] AC-DC power supplies often use flyback circuits to achieve higher power density and conversion efficiency. Traditional flyback circuits typically operate in a hard-switching state, resulting in high switching and capacitive losses. These losses increase with increasing operating frequency. Compared to traditional flyback circuits, active clamp flyback (ACF) circuits achieve zero voltage switching (ZVS) of the switch and recover leakage inductance energy, significantly improving conversion efficiency while enabling high-frequency operation. ACF circuits can be categorized as complementary active clamp flyback and non-complementary active clamp flyback based on the control logic of the auxiliary switch (also called auxiliary switch) and the main power switch (also called main power switch). The difference lies in the driving waveform of the main power switch. In complementary active clamp flybacks, the driving waveform of the main power switch is complementary, with a dead time between the two. In non-complementary active clamp flybacks, the auxiliary switch is only switched on for a short pulse, creating the conditions for ZVS of the main power switch.

[0004] In existing technology, active clamping circuits incorporate additional clamping capacitors compared to traditional flyback circuits. Before the main power switch turns on, a current flows in the opposite direction through the magnetizing inductor. After the auxiliary switch turns off, the negative current in the magnetizing inductor discharges the junction capacitance of the main power switch. When the voltage across the main power switch drops to zero, the main power switch turns on, achieving ZVS (zero voltage switching) and reducing switching losses.

[0005] However, during the on-state of the main power switch, the voltage of the clamping capacitor is higher than the reflected voltage of the secondary side of the transformer, causing the SR on the secondary side to turn on. The energy of the clamping capacitor is transferred to the output side through the transformer, resulting in a large current and thus a large loss.

[0006] Summary of the Invention

[0007] In the first aspect, the present application provides an active clamping circuit, which is connected to the primary winding of the transformer after being connected in parallel with the main power switch tube, and the clamping circuit includes: a first energy storage element, a first branch, and a second branch; the first branch and the second branch are connected in parallel and in series with the first energy storage element; the first branch includes a second energy storage element, and the second branch includes an auxiliary switch tube; wherein, the first energy storage element and the first branch are turned on to form a clamping loop, and the first energy storage element and the second energy storage element absorb the leakage inductance energy of the primary winding through the clamping loop after the main power tube is turned off; when the first energy storage element and the second branch are turned on to form a reverse excitation loop, the first energy storage element discharges when the auxiliary switch tube is turned on, and the clamping circuit is energized for the reverse excitation of the transformer.

[0008] Since the voltage across the clamp circuit is the sum of the voltages of the first energy storage element and the second energy storage element when it is forward charged (that is, when the main power tube is turned off), and only the voltage of the first energy storage element is present during discharge, when the transformer is reversely excited, the excitation voltage is less than the reflected voltage of the secondary winding, so that the secondary rectifier tube will not be turned on, thereby eliminating the forward energy transfer to the secondary side and reducing losses.

[0009] In a possible implementation, the first branch further includes: a first diode; the first diode is connected in series between the first energy storage element and the second energy storage element; the second branch further includes: a second diode, the second diode is connected in series between the first energy storage element and the auxiliary switch tube.

[0010] In one possible implementation, the anode of the first diode is connected to the first energy storage element, the cathode of the first diode is connected to the second energy storage element, and the first diode is configured to block the first energy storage element from releasing energy (that is, to block the reverse current relative to the first diode from flowing to the first energy storage element).

[0011] In one possible implementation, the anode of the second diode is connected to the auxiliary switch tube, the cathode of the second diode is connected to the first energy storage element, and the second diode is configured to block the first energy storage element from storing energy (that is, to block the reverse current relative to the second diode from flowing to the auxiliary switch tube).

[0012] In a possible implementation, when the clamping circuit is in a forward clamping state (or may be called a forward charging state), the clamping voltage of the main switch tube is the sum of the voltages of the first energy storage element and the second energy storage element.

[0013] In a possible implementation, the clamping circuit further includes a controller connected to the main power switch tube and the auxiliary switch tube, and the controller is configured to sequentially perform the following operations:

[0014] When the main power switch tube and the auxiliary switch tube are in the off state and the voltage across the main power switch tube drops to 0, switching the main power switch tube to the on state, thereby allowing current to flow through a main power circuit, wherein the main power circuit includes the primary winding and the main power switch tube;

[0015] After a first time period in which the main power switch is switched to an on state, the main power switch is switched from an on state to an off state, and after a dead time, the auxiliary switch is switched from an off state to an on state, thereby allowing current to flow through a clamping loop and allowing the first energy storage element and the second energy storage element to absorb leakage inductance energy of the transformer through the clamping loop, wherein the clamping loop includes the primary winding, the first energy storage element, and the second energy storage element;

[0016] When the current flowing through the primary winding becomes zero, the auxiliary switch tube is switched from the on state to the off state, and is switched to the on state after a second time period, thereby allowing current to flow through the reverse excitation circuit and allowing the first energy storage element to reversely excite and charge the transformer through the reverse excitation circuit. The reverse excitation circuit includes the first energy storage element, the primary winding and the auxiliary switch tube.

[0017] In a possible implementation, the controller is further configured to: based on the energy charging degree of the first energy storage element for reverse excitation of the transformer, switch the main power switch tube to an on state to achieve zero voltage switching.

[0018] In a possible implementation, the first energy storage element is a capacitor, and the second energy storage element is a capacitor or a primary auxiliary winding.

[0019] In a second aspect, the present application provides a control method, which is applied to a controller in an active clamping circuit, wherein the clamping circuit is connected to the primary winding of a transformer after being connected in parallel with a main power switch tube, and the clamping circuit includes: a first energy storage element, a first branch, and a second branch; the first branch and the second branch are connected in parallel with the first energy storage element in series; the first branch includes a second energy storage element, and the second branch includes an auxiliary switch tube; the controller is connected to the main power switch tube and the auxiliary switch tube; the method includes: when the main power switch tube and the auxiliary switch tube are in an off state and the voltage across the main power switch tube drops to 0, switching the main power switch tube to an on state, thereby allowing current to flow through the main power circuit, wherein the main power circuit includes the primary winding and the main power switch tube; after switching the main power switch tube to After a first time period in the on-state, the main power switch tube is switched from the on-state to the off-state, and after a dead time, the auxiliary switch tube is switched from the off-state to the on-state, thereby allowing current to flow through the clamping circuit and allowing the first energy storage element and the second energy storage element to absorb the leakage inductance energy of the transformer through the clamping circuit, wherein the clamping circuit includes the primary winding, the first energy storage element and the second energy storage element; when the current flowing through the primary winding becomes 0, the auxiliary switch tube is switched from the on-state to the off-state, and is switched to the on-state after a second time period, thereby allowing current to flow through the reverse excitation circuit and allowing the first energy storage element to reverse excite and charge the transformer through the reverse excitation circuit, wherein the reverse excitation circuit includes the first energy storage element, the primary winding and the auxiliary switch tube.

[0020] In one possible implementation, the method further includes: switching the main power switch tube to an on state and switching the auxiliary switch tube to an off state, thereby allowing current to flow through a main power circuit, wherein the main power circuit includes the primary winding and the main power switch tube;

[0021] In a possible implementation, the method further includes: switching the main power switch tube to an on state based on the energy charging degree of the first energy storage element for reverse excitation of the transformer to achieve zero voltage switching.

[0022] In a possible implementation, the first energy storage element is a capacitor, and the second energy storage element is a capacitor or a primary auxiliary winding.

[0023] In a possible implementation, when the clamp circuit is in a forward charging state, the first energy storage element and the first branch are connected to form a clamp loop; the first energy storage element and the second energy storage element absorb leakage inductance energy of the primary winding through the clamp loop.

[0024] In a possible implementation, when the clamping circuit is in a reverse excitation charging state for the transformer, the first energy storage element and the second branch are turned on to form a reverse excitation loop.

[0025] In a possible implementation, the first branch further includes: a first diode; the first diode is connected in series between the first energy storage element and the second energy storage element; the second branch further includes: a second diode, the second diode is connected in series between the first energy storage element and the auxiliary switch tube.

[0026] In a possible implementation, the anode of the first diode is connected to the first energy storage element, the cathode of the first diode is connected to the second energy storage element, and the first diode is configured to block reverse current relative to the first diode from flowing toward the first energy storage element.

[0027] In a possible implementation, the anode of the second diode is connected to the auxiliary switch tube, the cathode of the second diode is connected to the first energy storage element, and the second diode is configured to block reverse current relative to the second diode from flowing toward the auxiliary switch tube.

[0028] In a possible implementation, when the clamping circuit is in a forward charging state, the clamping voltage of the main switch tube is the sum of the voltages of the first energy storage element and the second energy storage element.

[0029] In a third aspect, the present application provides an active clamp flyback converter, comprising:

[0030] The active clamping circuit and transformer according to any one of the first aspects; the clamping circuit is connected in parallel with the main power switch tube and then connected to the primary winding of the transformer.

[0031] In a fourth aspect, the present application provides a switching power supply, comprising the active clamping circuit described in any one of the first aspects.

[0032] In a fifth aspect, the present application provides a controller for use in an active clamping circuit, wherein the clamping circuit is connected to the primary winding of a transformer after being connected in parallel with a main power switch tube, and the clamping circuit includes: a first energy storage element, a first branch, and a second branch; the first branch and the second branch are connected in parallel and connected in series with the first energy storage element; the first branch includes a second energy storage element, and the second branch includes an auxiliary switch tube; the controller is connected to the main power switch tube and the auxiliary switch tube; the controller is used to: when the main power switch tube and the auxiliary switch tube are in the off state and the voltage across the main power switch tube drops to 0, switch the main power switch tube to the on state, thereby allowing current to flow through the main power circuit, wherein the main power circuit includes the primary winding and the main power switch tube; when switching the main power switch tube to the on state After a first time period in the on-state, the main power switch tube is switched from the on-state to the off-state, and after a dead time, the auxiliary switch tube is switched from the off-state to the on-state, thereby allowing current to flow through the clamping circuit and allowing the first energy storage element and the second energy storage element to absorb the leakage inductance energy of the transformer through the clamping circuit, wherein the clamping circuit includes the primary winding, the first energy storage element, and the second energy storage element; when the current flowing through the primary winding becomes 0, the auxiliary switch tube is switched from the on-state to the off-state, and is switched to the on-state after a second time period, thereby allowing current to flow through the reverse excitation circuit and allowing the first energy storage element to reverse excite and charge the transformer through the reverse excitation circuit, wherein the reverse excitation circuit includes the first energy storage element, the primary winding, and the auxiliary switch tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1 is a schematic diagram of a circuit structure of an active clamping circuit;

[0034] Figure 2 is a schematic diagram of signal control;

[0035] Figure 3 is a schematic diagram of signal control;

[0036] FIG4 is a schematic diagram of a circuit structure of an active clamping circuit;

[0037] FIG5 is a flowchart illustrating a control method. DETAILED DESCRIPTION

[0038] The following describes the embodiments of the present invention in conjunction with the accompanying drawings. The terms used in the embodiments of the present invention are only used to explain the specific embodiments of the present invention, and are not intended to limit the present invention.

[0039] The embodiments of the present application are described below in conjunction with the accompanying drawings. Those skilled in the art will appreciate that, with the development of technology and the emergence of new scenarios, the technical solutions provided in the embodiments of the present application are also applicable to similar technical problems.

[0040] The terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the terms used in this way can be interchangeable under appropriate circumstances, and this is merely a way of distinguishing the objects of the same attributes when describing them in the embodiments of the present application. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, so that the process, method, system, product or equipment comprising a series of units need not be limited to those units, but may include other units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0041] As used herein, the terms "substantially," "about," and similar terms are used as terms of approximation, not as terms of degree, and are intended to take into account the inherent variations in measurements or calculations that one of ordinary skill in the art would recognize. Furthermore, the use of "may" when describing embodiments of the present invention refers to "one or more possible embodiments." As used herein, the terms "use," "using," and "used" may be considered synonymous with the terms "utilize," "utilizing," and "utilized," respectively. Additionally, the term "exemplary" is intended to refer to an example or illustration.

[0042] The following describes some concepts involved in this application:

[0043] (1) Adapter: refers to a device that has a voltage conversion function and supplies power to electronic equipment (also known as terminal equipment). It is also called a charger, switching power supply, charger, or power converter.

[0044] (2) Super Charger: refers to an adapter or charger that can charge a battery-powered device such as a mobile phone or computer quickly, shortening the charging time. It is also commonly called a Super Charger, rapid charger, fast charge, or quick charge.

[0045] (3) Half-bridge: It refers to an electrical topology structure in a switching power supply that uses two power switching tubes to work alternately to achieve power transmission. The main switching bridge is also called the main tube or the first switch; the auxiliary switching bridge is also called the radial tube or the second switch.

[0046] (4) Asymmetric half bridge: In the present invention, it means that the duty ratio of the upper bridge and the lower bridge is not 50% symmetrical.

[0047] (5) Controller IC: refers to the control unit of the product, which implements waveform detection and action logic.

[0048] (6) Transformer: The component in the switching power supply that is responsible for transmitting power and converting voltage.

[0049] (7) Auxiliary winding: The winding in the transformer that is not responsible for power transmission, such as the VCC winding.

[0050] (8) Primary winding: The winding placed on the primary side of the transformer responsible for input voltage and current.

[0051] (9) Secondary winding: The winding placed on the secondary side of the transformer responsible for output voltage and current.

[0052] In order to enable people skilled in the art to better understand the present application, the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0053] FIG1 is a schematic diagram of an active clamping circuit.

[0054] As shown in Figure 1 , an embodiment of the present application provides an active clamping circuit, wherein the active clamping circuit belongs to an active clamping flyback converter.

[0055] As shown in Figure 1, the active-clamp flyback converter includes a transformer T1, which includes a primary winding Np and a secondary winding Ns. On the output side of transformer T1, or the secondary side, the active-clamp flyback converter also includes an output voltage Vout (abbreviated as V0 in Figure 1), a corresponding output capacitor Cout (abbreviated as C0 in Figure 1), and a secondary synchronous rectifier (SR) connected in series with the secondary winding Ns. It should be understood that the SR can also be replaced with other types of rectifiers.

[0056] Because the windings of transformer T1 are not ideally tightly coupled, parasitic leakage inductance exists. This parasitic leakage inductance is represented by the inductance Lr connected in series with the primary winding Np. This inductance Lr should be understood as an intrinsic part of the primary winding Np. The moving and static points of the primary winding Np and the secondary winding Ns, respectively, are used solely for the purpose of explaining the reference direction of their respective induced electromotive forces and should be understood as relative. That is, the moving point of one end of the primary winding Np or the secondary winding Ns is relative to the static point of the other end.

[0057] On the input side of the transformer T1, that is, the primary side, the active clamp flyback converter also includes an input voltage source Vin for representing the input, a corresponding input capacitor Cin, and a flyback circuit. L After being connected in parallel, it is connected to the primary winding Np of transformer T1.

[0058] Compared to traditional flyback circuits, the active clamp circuit incorporates a clamping switch and a clamping capacitor. Before the main power switch turns on, a current in the opposite direction flows through the magnetizing inductor. After the clamping switch turns off, the negative current in the magnetizing inductor discharges the junction capacitance of the main power switch. When the voltage across the main power switch drops to zero, the main power switch turns on, achieving zero-voltage (ZVS) turn-on and reducing switching losses.

[0059] However, during the period when the clamp switch tube is turned on, since the voltage of the clamp capacitor is higher than the reflected voltage of the secondary side of the transformer, the SR on the secondary side is turned on, and the energy of the clamp capacitor is transferred to the output side through the transformer, resulting in a large current, which in turn leads to a large loss problem.

[0060] In order to solve the above problems, an embodiment of the present application designs a flyback circuit.

[0061] The clamping circuit includes: a first energy storage element (e.g., capacitor Cr shown in FIG1 ), a first branch, and a second branch. The first branch and the second branch are connected in parallel and then in series with the first energy storage element. The first branch includes the second energy storage element (e.g., capacitor C1 shown in FIG1 ). The flyback circuit can be connected in parallel to the main power switch tube Q L Both ends.

[0062] In one possible implementation, the first branch further includes: a first diode D1, which is connected in series between the first energy storage element and the second energy storage element; an anode of the first diode D1 is connected to the first energy storage element, and a cathode of the first diode D1 is connected to the second energy storage element, and the first diode D1 can block a reverse current relative to the first diode D1 from flowing toward the first energy storage element.

[0063] In a possible implementation, the second branch includes an auxiliary switch tube Q A , and a second diode D2, the second diode D2 is connected in series between the first energy storage element and the auxiliary switch tube Q A The anode of the second diode D2 is connected to the auxiliary switch tube Q AThe cathode of the second diode D2 is connected to the first energy storage element, and the second diode D2 can block the reverse current relative to the second diode D2 from flowing to the auxiliary switch tube Q A .

[0064] In some exemplary embodiments, the first diode D1 and the second diode D2 can be implemented using suitable means in the prior art, such as point-contact diodes, surface-contact diodes, or planar diodes. These can be adjusted and improved according to specific application environments and are not specifically limited here.

[0065] Among them, the auxiliary switch tube is also called the upper tube Q A The main power switch tube is also called the lower tube Q L Optional, auxiliary switch tube Q A And the main power switch tube Q L It is an N-channel enhancement type metal oxide semiconductor field effect transistor (MOSFET), and the auxiliary switch tube Q A And the main power switch tube Q L The anode of each parasitic diode is connected to the corresponding source and the cathode is connected to the corresponding drain. L Connected between the input voltage source Vin and the primary winding Np.

[0066] In a possible implementation, the first energy storage element and the second energy storage element are capacitors. For example, as shown in FIG1 , the first energy storage element is a capacitor Cr, and the second energy storage element is a capacitor C1.

[0067] In a possible implementation, the first energy storage element is a capacitor, and the second energy storage element is an auxiliary winding of the primary side. For example, as shown in FIG4 , the first energy storage element is a capacitor Cr, and the second energy storage element is an auxiliary winding.

[0068] It should be understood that the first energy storage element and the second energy storage element may include one or more elements, and when the number is more than one, the types of the elements may be the same or different, which is not limited in the embodiment of the present application.

[0069] The active clamp flyback converter shown in Figure 1 is based on the auxiliary switch tube Q A And the main power switch tube Q L The control logic can be used for complementary active clamp flyback and non-complementary active clamp flyback. Among them, complementary active clamp flyback refers to the driving waveform of the main power switch tube being complementary, and there is a dead time between the two; non-complementary active clamp flyback refers to the auxiliary switch tube QA Only short-time pulses are turned on, so that the main power switch tube Q L Can achieve zero voltage switching.

[0070] In one working state, the primary power circuit can be turned on by controlling the on and off of the main power switch tube and the auxiliary switch tube. The main power circuit is introduced below:

[0071] In one possible implementation, the clamping circuit further includes a controller, which is connected to the main power switch tube and the auxiliary switch tube, and is configured to perform the following operations: switching the main power switch tube to an on state and switching the auxiliary switch tube to an off state, thereby allowing current to flow through a main power loop, wherein the main power loop includes the primary winding and the main power switch tube.

[0072] Referring to Figure 2, Figure 2 is a schematic diagram of the control signal of the non-complementary active clamp flyback. When the main power switch tube and the auxiliary switch tube are in the off state and the voltage across the main power switch tube drops to 0, the main power switch tube is switched to the on state, thereby allowing the current to flow through the main power circuit, wherein the main power circuit includes the primary winding and the main power switch tube. At time t0, the main power switch tube QL is turned on and the auxiliary switch tube QA is turned off. The input voltage source Vin charges the primary winding Np of the transformer T1 and also charges the parasitic inductance Lr. That is, the input voltage source Vin excites the excitation inductance of the transformer T1. At this time, the active clamp flyback converter includes the main power circuit. The main power circuit starts from the input voltage source Vin. The input voltage passes through the input voltage source Vin, the primary winding Np (including the parasitic inductance Lr), the main power switch tube QL, and the primary winding Np (including the parasitic inductance Lr). L , and finally returns to the input voltage source Vin.

[0073] In one working state, the clamping loop of the flyback circuit can be turned on by controlling the turn-off and turn-on of the main power switch tube and the auxiliary switch tube. The following is an introduction:

[0074] In one possible implementation, the main power switch tube can be switched from the on state to the off state after a first time period (for example, t1 in Figure 2), and the auxiliary switch tube can be switched from the off state to the on state after the dead time, thereby allowing current to flow through the clamping loop and allowing the first energy storage element and the second energy storage element to absorb the leakage inductance energy of the transformer through the clamping loop, wherein the clamping loop includes the primary winding, the first energy storage element, and the second energy storage element.

[0075] In one possible implementation, the controller can control the main power switch tube Q LTurn off the auxiliary switch Q A Open, because the main power switch tube Q L When the input voltage is removed by shutdown, transformer T1's secondary winding Ns generates a reverse output voltage on the primary winding Np to maintain a constant magnetic flux. Specifically, the energy stored in the transformer (including parasitic inductance L1) is transferred to the energy storage elements (first and second energy storage elements) of the clamping circuit for charging. At this point, the active clamp flyback converter includes a clamping circuit. The clamping circuit begins at the primary winding Np. The reverse output voltage sequentially passes through the primary winding Np's active point, the first storage element (e.g., capacitor Cr shown in Figure 1), the first diode D1, the second storage element (e.g., capacitor C1 shown in Figure 1), the input voltage source Vin, and finally returns to the primary winding Np's static point.

[0076] When the clamping circuit is conducting and the flyback circuit is in a forward charging state, the first energy storage element and the first branch circuit conduct to form a clamping circuit. The first and second energy storage elements absorb the leakage inductance energy of the primary winding through the clamping circuit. At this time, the clamping voltage of the main switch is the sum of the voltages of the first and second energy storage elements.

[0077] Refer to Figure 2, which shows the control signal of the non-complementary active clamp flyback. At time t1, the excitation current reaches the preset value, turning off the main power switch tube Q L After the dead zone, the auxiliary switch tube Q is turned on. A At this time, the transformer primary current flows through the first energy storage element Cr and the second energy storage element C1, the two capacitors are connected in series, and the main power switch tube Q L The clamping voltage is the sum of the two capacitor voltages.

[0078] In one working state, the main power switch Q L and auxiliary switch tube Q A The turn-off and turn-on of the flyback circuit make the reverse excitation circuit conductive, which is introduced below:

[0079] In a possible implementation, when the clamping circuit is in a reverse excitation charging state for the transformer, the first energy storage element and the second branch are turned on to form a reverse excitation loop.

[0080] In a possible implementation, the main power switch tube Q is switched L to the off state and switches the auxiliary switch Q Ato the on state, thereby allowing the current to flow through the reverse excitation circuit and allowing the first energy storage element to reversely excite and charge the transformer through the reverse excitation circuit (for example, at time t3 in FIG2 , wherein the time period from the auxiliary switch tube being off to being on is the second time period), the reverse excitation circuit includes the first energy storage element, the primary winding, and the auxiliary switch tube Q A .

[0081] Refer to Figure 2, which shows the control signal of the non-complementary active clamp flyback. At time t3, the auxiliary switch tube Q is turned on. A , the first energy storage element Cr reversely excites the magnetizing inductor, generating a negative current. When the clamp circuit is forward-charging, the voltage across it is the sum of the voltages of the first and second energy storage elements, while during discharge, only the voltage of the first energy storage element is present. When reverse-exciting the transformer, the excitation voltage is less than the reflected voltage of the secondary winding, preventing the secondary winding SR from turning on. This eliminates the forward transfer of energy to the secondary side, reducing losses.

[0082] In this way, the active clamping circuit ensures that the excitation voltage generated on the secondary side of the transformer by the clamping element for reverse excitation and energizing the transformer will not change the reverse cutoff state of the secondary rectifier tube, thereby not causing a peak current to flow through the auxiliary switch tube and the secondary rectifier tube, effectively avoiding the problem of excess energy being transferred to the secondary side of the transformer in the forward direction at the moment the auxiliary switch tube is turned on.

[0083] The embodiments of the present application can be applicable to application scenarios such as low-power AC-DC power supplies, switching power supplies requiring high power density and high conversion efficiency, miniaturized high-efficiency power supply components, and consumer electronic products.

[0084] In a possible implementation, the controller is further configured to: based on the energy charging degree of the first energy storage element for reverse excitation of the transformer, switch the main power switch tube to an on state to achieve zero voltage switching.

[0085] Refer to Figure 2, which shows the control signal of the non-complementary active clamp flyback. At time t4, when the auxiliary switch tube Q A After shutdown, this negative current is fed to the main power switch tube Q L The junction capacitance is discharged; at time t5, the main power switch tube Q L The Vds drops to 0, turning on the main power switch Q L , achieving ZVS turn-on and reducing switching losses.

[0086] In addition, the embodiment of the present application can also be applied to a complementary active clamp flyback. For example, referring to FIG. 3 , FIG. 3 is a schematic diagram of signal control in a critical conduction mode (CRM) mode. As shown in FIG. 3 , the main power switch tube Q L and auxiliary switch tube Q A In addition to leaving the switch dead zone, the two switch tubes are complementary turned on, and the auxiliary switch tube Q A After the excitation current drops to 0, it continues to conduct, reversely excites the excitation inductor, and forms a negative current, which is the basis for the next stage to realize the main power switch tube Q L Create conditions for soft switching.

[0087] In some exemplary embodiments, a switching power supply includes the active clamping circuit shown in FIG. 1 and FIG. 3 .

[0088] In addition, referring to FIG5 , FIG5 is a flowchart of a control method provided in an embodiment of the present application. The method can be applied to a controller in an active clamping circuit (e.g., the circuit described in FIG1 or FIG4 ), wherein the clamping circuit is connected in parallel with the main power switch tube and then connected to the primary winding of the transformer. The clamping circuit includes: a first energy storage element, a first branch, and a second branch; the first branch and the second branch are connected in parallel and then connected in series with the first energy storage element; the first branch includes a second energy storage element, and the second branch includes an auxiliary switch tube; the controller is connected to the main power switch tube and the auxiliary switch tube;

[0089] The method comprises:

[0090] 501. When the main power switch and the auxiliary switch are in the off state and the voltage across the main power switch drops to 0, switch the main power switch to the on state, thereby allowing current to flow through a main power circuit, wherein the main power circuit includes the primary winding and the main power switch.

[0091] 502. After a first time period in which the main power switch is switched to the on state, the main power switch is switched from the on state to the off state, and after a dead time, the auxiliary switch is switched from the off state to the on state, thereby allowing current to flow through a clamping loop and allowing the first energy storage element and the second energy storage element to absorb leakage inductance energy of the transformer through the clamping loop, wherein the clamping loop includes the primary winding, the first energy storage element, and the second energy storage element.

[0092] In one possible implementation, the controller can control the main power switch tube Q L Turn off the auxiliary switch Q A Open, because the main power switch tube Q LWhen the input voltage is removed during shutdown, the secondary winding Ns of transformer T1 generates a reverse output voltage on the primary winding Np to maintain a constant magnetic flux. Specifically, the energy stored in the transformer (including parasitic inductance L1) is transferred to the energy storage elements (first and second energy storage elements) of the clamping circuit for charging. At this point, the active clamp flyback converter includes a clamping circuit. The clamping circuit begins at the primary winding Np. The reverse output voltage sequentially passes through the static point of the primary winding Np, the first storage element (e.g., capacitor Cr shown in Figure 1), the first diode D1, the second storage element (e.g., capacitor C1 shown in Figure 1), the input voltage source Vin, and finally returns to the moving point of the primary winding Np.

[0093] When the clamping circuit is conducting and the flyback circuit is in a forward charging state, the first energy storage element and the first branch circuit conduct to form a clamping circuit. The first and second energy storage elements absorb the leakage inductance energy of the primary winding through the clamping circuit. At this time, the clamping voltage of the main switch is the sum of the voltages of the first and second energy storage elements.

[0094] 503. When the current flowing through the primary winding becomes 0, switch the auxiliary switch tube from the on state to the off state, and switch to the on state after a second time period, thereby allowing current to flow through the reverse excitation circuit and allowing the first energy storage element to reverse excite and charge the transformer through the reverse excitation circuit, wherein the reverse excitation circuit includes the first energy storage element, the primary winding and the auxiliary switch tube.

[0095] In a possible implementation, the main power switch tube Q is switched L to the off state and switches the auxiliary switch Q A to the on state, thereby allowing the current to flow through the reverse excitation circuit and allowing the first energy storage element to reverse excite and charge the transformer through the reverse excitation circuit, the reverse excitation circuit including the first energy storage element, the primary winding and the auxiliary switch tube Q A .

[0096] Refer to Figure 2, which shows the control signal of the non-complementary active clamp flyback. At time t3, the auxiliary switch tube Q is turned on. A , the first energy storage element Cr reversely excites the excitation inductor to form a negative current.

[0097] When the clamp circuit is forward charged, the voltage across the two ends is the sum of the voltages of the first energy storage element and the second energy storage element, and when discharging, only the voltage of the first energy storage element is present. When the transformer is reversely excited, the excitation voltage is less than the reflected voltage of the secondary winding, so that the secondary rectifier tube will not be turned on, thus eliminating the forward energy to the secondary side, thereby reducing losses.

[0098] In this way, the active clamping circuit ensures that the excitation voltage generated on the secondary side of the transformer by the clamping element for reverse excitation and energizing the transformer will not change the reverse cutoff state of the secondary rectifier tube, thereby not causing a peak current to flow through the auxiliary switch tube and the secondary rectifier tube, effectively avoiding the problem of excess energy being transferred to the secondary side of the transformer in the forward direction at the moment the auxiliary switch tube is turned on.

[0099] In one possible implementation, the method further includes:

[0100] Switching the main power switch tube to an on state and switching the auxiliary switch tube to an off state, thereby allowing current to flow through a main power circuit, wherein the main power circuit includes the primary winding and the main power switch tube;

[0101] In one possible implementation, the method further includes:

[0102] Based on the energy charging degree of the first energy storage element for reverse excitation of the transformer, the main power switch tube is switched to the on state to achieve zero voltage switching.

[0103] In a possible implementation, the first energy storage element is a capacitor, and the second energy storage element is a capacitor or a primary auxiliary winding.

[0104] In a possible implementation, when the clamp circuit is in a forward charging state, the first energy storage element and the first branch are connected to form a clamp loop; the first energy storage element and the second energy storage element absorb leakage inductance energy of the primary winding through the clamp loop.

[0105] In a possible implementation, when the clamping circuit is in a reverse excitation charging state for the transformer, the first energy storage element and the second branch are turned on to form a reverse excitation loop.

[0106] In a possible implementation, the first branch further includes: a first diode; the first diode is connected in series between the first energy storage element and the second energy storage element; the second branch further includes: a second diode, the second diode is connected in series between the first energy storage element and the auxiliary switch tube.

[0107] In a possible implementation, the anode of the first diode is connected to the first energy storage element, the cathode of the first diode is connected to the second energy storage element, and the first diode is configured to block reverse current relative to the first diode from flowing toward the first energy storage element.

[0108] In a possible implementation, the anode of the second diode is connected to the auxiliary switch tube, the cathode of the second diode is connected to the first energy storage element, and the second diode is configured to block reverse current relative to the second diode from flowing toward the auxiliary switch tube.

[0109] In a possible implementation, when the clamping circuit is in a forward charging state, the clamping voltage of the main switch tube is the sum of the voltages of the first energy storage element and the second energy storage element.

[0110] The specific embodiments provided herein can be implemented in any one or combination of hardware, software, firmware or solid-state logic circuits, and can be implemented in conjunction with signal processing, control and / or dedicated circuits. The equipment or apparatus provided in the specific embodiments of the present application may include one or more processors (e.g., microprocessors, controllers, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), etc.), which process various computer-executable instructions to control the operation of the equipment or apparatus. The equipment or apparatus provided in the specific embodiments of the present application may include a system bus or a data transmission system connecting various components together. The system bus may include any one or a combination of different bus structures, such as a memory bus or a memory controller, a peripheral bus, a universal serial bus and / or a processor or local bus utilizing any one of a variety of bus architectures. The equipment or apparatus provided in the specific embodiments of the present application may be provided separately, may be part of a system, or may be part of other equipment or apparatus.

[0111] The specific embodiments provided in this application may include or be combined with a computer-readable storage medium, such as one or more storage devices capable of providing non-transitory data storage. The computer-readable storage medium / storage device may be configured to store data, programmers and / or instructions that, when executed by a processor of the device or apparatus provided in the specific embodiments of this application, enable these devices or apparatuses to perform relevant operations. The computer-readable storage medium / storage device may include one or more of the following features: volatility, non-volatility, dynamic, static, readable / writable, read-only, random access, sequential access, location addressability, file addressability, and content addressability. In one or more exemplary embodiments, the computer-readable storage medium / storage device may be integrated into the device or apparatus provided in the specific embodiments of this application or belong to a common system. Computer-readable storage media / storage devices may include optical storage devices, semiconductor storage devices and / or magnetic storage devices, etc., and may also include random access memory (RAM), flash memory, read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disks, removable disks, recordable and / or rewritable compact disks (CDs), digital versatile disks (DVDs), mass storage media devices or any other form of suitable storage media.

[0112] The above is an implementation method of the embodiment of the present application. It should be noted that the steps in the method described in the specific embodiment of the present application can be adjusted in order, combined and deleted according to actual needs. In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, please refer to the relevant description of other embodiments. It is understandable that the structures shown in the embodiments of the present application and the drawings do not constitute specific limitations on the relevant devices or systems. In other embodiments of the present application, the relevant devices or systems may include more or fewer components than the specific embodiments and drawings, or combine certain components, or split certain components, or have different component arrangements. Those skilled in the art will understand that, without departing from the spirit and scope of the specific embodiments of the present application, various modifications or changes can be made to the arrangement, operation and details of the methods and equipment recorded in the specific embodiments; without departing from the principles of the embodiments of the present application, several improvements and modifications can be made, and these improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. An active clamping circuit, characterized in that: The clamping circuit is connected to the primary winding of the transformer after being connected in parallel with the main power switch tube. The clamping circuit includes: A first energy storage element, a first branch, and a second branch; The first branch and the second branch are connected in parallel and then in series with the first energy storage element; The first branch includes a second energy storage element, and the second branch includes an auxiliary switch tube; The first energy storage element and the first branch are turned on to form a clamping loop, and after the main power tube is turned off, the first energy storage element and the second energy storage element absorb the leakage inductance energy of the primary winding through the clamping loop; When the first energy storage element and the second branch are turned on to form a reverse excitation circuit, the first energy storage element discharges when the auxiliary switch tube is turned on to charge the reverse excitation of the transformer.

2. The active clamping circuit according to claim 1, characterized in that: The first branch further includes: a first diode; the first diode is connected in series between the first energy storage element and the second energy storage element; The second branch further includes: a second diode, which is connected in series between the first energy storage element and the auxiliary switch tube.

3. The active clamping circuit according to claim 2, characterized in that: An anode of the first diode is connected to the first energy storage element, a cathode of the first diode is connected to the second energy storage element, and the first diode is configured to block the first energy storage element from releasing energy.

4. The active clamping circuit according to claim 2 or 3, characterized in that: An anode of the second diode is connected to the auxiliary switch tube, a cathode of the second diode is connected to the first energy storage element, and the second diode is configured to block the first energy storage element from storing energy.

5. The active clamping circuit according to any one of claims 1 to 4, characterized in that: When the clamp circuit is in a forward clamp state, the clamp voltage of the main switch tube is the sum of the voltages of the first energy storage element and the second energy storage element.

6. The active clamping circuit according to any one of claims 1 to 5, characterized in that: The clamping circuit further includes a controller, which is connected to the main power switch tube and the auxiliary switch tube, and is configured to perform the following operations in sequence: When the main power switch tube and the auxiliary switch tube are in the off state and the voltage across the main power switch tube drops to 0, the main power switch tube is switched to the on state, thereby allowing current to flow through the main power circuit, wherein the main power circuit includes the primary winding and the main power switch tube; After a first time period when the main power switch tube is switched to an on state, the main power switch tube is switched from an on state to an off state, and after a dead time, the auxiliary switch tube is switched from an off state to an on state, thereby allowing current to flow through the clamping loop and allowing the first energy storage element and the second energy storage element to absorb leakage inductance energy of the transformer through the clamping loop, wherein the clamping loop includes the primary winding, the first energy storage element, and the second energy storage element; When the current flowing through the primary winding becomes 0, the auxiliary switch tube is switched from the on state to the off state, and is switched to the on state after a second time period, thereby allowing the current to flow through the reverse excitation circuit and allowing the first energy storage element to reverse excite and charge the transformer through the reverse excitation circuit. The reverse excitation circuit includes the first energy storage element, the primary winding and the auxiliary switch tube.

7. The active clamping circuit according to claim 6, characterized in that: The controller is also used for: Based on the energy charging degree of the first energy storage element for reverse excitation of the transformer, the main power switch tube is switched to an on state to achieve zero voltage switching.

8. The active clamping circuit according to any one of claims 1 to 7, characterized in that: The first energy storage element is a capacitor, and the second energy storage element is a capacitor or a primary auxiliary winding.

9. A control method, applied to a controller in an active clamping circuit, wherein: The clamping circuit is connected to the primary winding of the transformer after being connected in parallel with the main power switch tube. The clamping circuit includes: a first energy storage element, a first branch and a second branch; the first branch and the second branch are connected in parallel and connected in series with the first energy storage element; the first branch includes a second energy storage element, and the second branch includes an auxiliary switch tube; the controller is connected to the main power switch tube and the auxiliary switch tube; the method includes: When the main power switch tube and the auxiliary switch tube are in the off state and the voltage across the main power switch tube drops to 0, the main power switch tube is switched to the on state, thereby allowing current to flow through the main power circuit, wherein the main power circuit includes the primary winding and the main power switch tube; After a first time period when the main power switch tube is switched to an on state, the main power switch tube is switched from an on state to an off state, and after a dead time, the auxiliary switch tube is switched from an off state to an on state, thereby allowing current to flow through the clamping loop and allowing the first energy storage element and the second energy storage element to absorb leakage inductance energy of the transformer through the clamping loop, wherein the clamping loop includes the primary winding, the first energy storage element, and the second energy storage element; When the current flowing through the primary winding becomes 0, the auxiliary switch tube is switched from the on state to the off state, and is switched to the on state after a second time period, thereby allowing the current to flow through the reverse excitation circuit and allowing the first energy storage element to reverse excite and charge the transformer through the reverse excitation circuit. The reverse excitation circuit includes the first energy storage element, the primary winding and the auxiliary switch tube.

10. An active clamp flyback converter, characterized in that: include: The active clamping circuit and transformer as claimed in any one of claims 1 to 8; The clamping circuit is connected to the primary winding of the transformer in parallel with the main power switch tube.

11. A switching power supply, characterized in that: The switching power supply comprises an active clamping circuit according to any one of claims 1-8.

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