Active clamping circuit, converter and power supply

Abstract

The active clamping circuit comprises a first energy storage element, a first branch circuit and a second branch circuit, 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 comprises a second energy storage element, and the second branch comprises an auxiliary switch tube; when the clamping circuit is in a forward charging state, the first energy storage element and the first branch are conducted to form a clamping loop; the first energy storage element and the second energy storage element absorb leakage inductance energy of the primary winding through the clamping loop; and when the clamping circuit is in a reverse excitation energy charging state for the transformer, the first energy storage element and the second branch are conducted to form a reverse excitation loop. As the voltage at the two ends is the sum of the voltage of the first energy storage element and the voltage of the second energy storage element during forward charging of the clamping circuit and is only the voltage of the first energy storage element during discharging, and the excitation voltage is smaller than the reflection voltage of the secondary winding during reverse excitation of the transformer, a secondary rectifier tube cannot be switched on, energy forward shock to the secondary side is eliminated, and the voltage of the secondary side is reduced. Therefore, the loss is reduced.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and particularly to an active clamp circuit, a converter, and a power supply. Background Art

[0002] An AC-DC power supply usually adopts a flyback circuit to obtain higher power density and higher conversion efficiency. In a traditional flyback circuit, the switching transistor usually operates in a hard-switching state, resulting in relatively large switching losses and capacitive losses, and the losses will increase as the operating frequency increases. Compared with the traditional flyback circuit, an Active Clamp Flyback (ACF) circuit can achieve Zero Voltage Switching (ZVS) of the switching transistor and recover the leakage inductance energy, thus significantly improving the conversion efficiency while enabling high-frequency operation. According to the control logic of the auxiliary switching transistor (also called the auxiliary switch) and the main power switching transistor (also called the main switch), the ACF circuit can be divided into a complementary active clamp flyback and a non-complementary active clamp flyback, and the difference lies in the driving waveform of the upper main power switching transistor. Among them, in the complementary active clamp flyback, the driving waveforms of the upper main power switching transistors are complementary, and there is a dead time between them; in the non-complementary active clamp flyback, the auxiliary switching transistor is only turned on for a short pulse to create conditions for ZVS of the main power switching transistor.

[0003] In the prior art, compared with the traditional flyback circuit, an additional clamping capacitor is added to the active clamp circuit. Before the main power switching transistor is turned on, the excitation inductor flows through currents in opposite directions. After the auxiliary switching transistor is turned off, the negative current of the excitation inductor discharges the junction capacitance of the main power switching transistor. When the voltage of the main power switching transistor drops to 0, the main power switching transistor is turned on, achieving ZVS turn-on and reducing switching losses.

[0004] However, during the turn-on period of the main power switching transistor, since the voltage of the clamping 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 clamping capacitor is transferred to the output side through the transformer, resulting in a relatively large current and thus a large loss problem. Summary of the Invention

[0005] In a first aspect, the present application provides an active clamping circuit. The clamping circuit is connected in parallel with a main power switch and then connected to the primary winding of a 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; wherein, the first energy storage element and the first branch are turned on to form a clamping loop, and after the main power switch 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 loop, the first energy storage element discharges when the auxiliary switch is turned on to charge the reverse excitation of the transformer. The clamping circuit

[0006] Since when the clamping circuit is charging forward (i.e., when the main power switch is turned off), the voltage across both ends is the sum of the voltages of the first energy storage element and the second energy storage element, and when discharging, it is only the voltage of the first energy storage element. When exciting the transformer in the reverse direction, the exciting voltage is less than the reflected voltage of the secondary winding, so that the secondary rectifier diode will not turn on, thus eliminating the energy being transferred to the secondary in the forward direction, thereby reducing the loss.

[0007] 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, and the second diode is connected in series between the first energy storage element and the auxiliary switch.

[0008] In a possible implementation, the anode of the first diode is connected to the first energy storage element, and the cathode of the first diode is connected to the second energy storage element. The first diode is configured to block the release of energy from the first energy storage element (i.e., block the reverse current relative to the first diode from flowing to the first energy storage element).

[0009] In a possible implementation, the anode of the second diode is connected to the auxiliary switch, and the cathode of the second diode is connected to the first energy storage element. The second diode is configured to block the storage of energy in the first energy storage element (i.e., block the reverse current relative to the second diode from flowing to the auxiliary switch).

[0010] In a possible implementation, when the clamping circuit is in the forward clamping state (or can be called the forward charging state), the clamping voltage of the main switch is the sum of the voltages of the first energy storage element and the second energy storage element.

[0011] In a possible implementation, the clamping circuit further includes a controller, the controller is connected to the main power switch and the auxiliary switch, and the controller is configured to sequentially perform the following operations:

[0012] 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 the current flowing through the main power loop to flow, where the main power loop includes the primary winding and the main power switch;

[0013] After a first time period of switching the main power switch to the on state, switch the main power switch from the on state to the off state, and after the dead time, switch the auxiliary switch from the off state to the on state, thereby allowing the current flowing through the clamping loop to flow 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, where the clamping loop includes the primary winding, the first energy storage element, and the second energy storage element;

[0014] When the current flowing through the primary winding becomes 0, switch the auxiliary switch from the on state to the off state, and switch to the on state after a second time period, thereby allowing the current flowing through the reverse excitation loop to flow and allowing the first energy storage element to perform reverse excitation charging on the transformer through the reverse excitation loop, where the reverse excitation loop includes the first energy storage element, the primary winding, and the auxiliary switch.

[0015] In a possible implementation, the controller is further configured to: based on the charging degree of the reverse excitation of the transformer by the first energy storage element, switch the main power switch to the on state to achieve zero voltage switching.

[0016] 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.

[0017] 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. 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; the controller is connected to the main power switch and the auxiliary switch; the method includes: 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, switching the main power switch to the on state, thereby allowing the current in the main power loop to flow, wherein the main power loop includes the primary winding and the main power switch; after a first time period of switching the main power switch to the on state, switching the main power switch from the on state to the off state, and after the dead time, switching the auxiliary switch from the off state to the on state, thereby allowing the current in the clamping loop to flow 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; when the current flowing through the primary winding becomes 0, switching the auxiliary switch from the on state to the off state and switching to the on state after a second time period, thereby allowing the current in the reverse excitation loop to flow and allowing the first energy storage element to perform reverse excitation charging on the transformer through the reverse excitation loop, and the reverse excitation loop includes the first energy storage element, the primary winding, and the auxiliary switch.

[0018] In a possible implementation, the method further includes: switching the main power switch to the on state and switching the auxiliary switch to the off state, thereby allowing the current in the main power loop to flow, wherein the main power loop includes the primary winding and the main power switch;

[0019] In a possible implementation, the method further includes: based on the charging degree of the reverse excitation of the transformer by the first energy storage element, switching the main power switch to the on state to achieve zero voltage switching.

[0020] 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.

[0021] In a possible implementation, when the clamping circuit is in the forward charging state, the first energy storage element and the first branch are turned on to form a clamping loop; the first energy storage element and the second energy storage element absorb the leakage inductance energy of the primary winding through the clamping loop.

[0022] In a possible implementation, when the clamping circuit is in the state of charging the reverse excitation of the transformer, the first energy storage element and the second branch are turned on to form a reverse excitation loop.

[0023] 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, and the second diode is connected in series between the first energy storage element and the auxiliary switch tube.

[0024] 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 the reverse current relative to the first diode from flowing to the first energy storage element.

[0025] 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 the reverse current relative to the second diode from flowing to the auxiliary switch tube.

[0026] In a possible implementation, when the clamping circuit is in the 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.

[0027] In a third aspect, the present application provides an active clamp flyback converter, including:

[0028] The active clamping circuit and the transformer according to any one of the first aspects; the clamping circuit is connected to the primary winding of the transformer after being connected in parallel with the main power switch tube.

[0029] In a fourth aspect, the present application provides a switching power supply, and the switching power supply includes the active clamping circuit according to any one of the first aspects.

[0030] Fifth aspect, the present application provides a controller applied to an active clamping circuit. In the circuit, the clamping circuit is connected to the primary winding of a transformer after being connected in parallel with a main power switch. 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; the controller is connected to the main power switch and the auxiliary switch; the controller is configured to: 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 the current in the main power loop to flow, where the main power loop includes the primary winding and the main power switch; after a first time period of switching the main power switch to the on state, switch the main power switch from the on state to the off state, and after the dead time, switch the auxiliary switch from the off state to the on state, thereby allowing the current in the clamping loop to flow 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, where 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, switch the auxiliary switch from the on state to the off state and switch to the on state after a second time period, thereby allowing the current in the reverse excitation loop to flow and allowing the first energy storage element to perform reverse excitation charging on the transformer through the reverse excitation loop, where the reverse excitation loop includes the first energy storage element, the primary winding, and the auxiliary switch. Description of the Drawings

[0031] Figure 1 Schematic diagram of the circuit structure of an active clamping circuit;

[0032] Figure 2 Schematic diagram of signal control;

[0033] Figure 3 Schematic diagram of signal control;

[0034] Figure 4 Schematic diagram of the circuit structure of an active clamping circuit;

[0035] Figure 5 Schematic diagram of the flow of a control method. Detailed Embodiments

[0036] The embodiments of the present invention will be described below with reference to the drawings in the embodiments of the present invention. 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.

[0037] The embodiments of the present application will be described below with reference to the accompanying drawings. As can be known to those of ordinary skill in the art, with the development of technology and the emergence of new scenarios, the technical solutions provided by the embodiments of the present application are equally applicable to similar technical problems.

[0038] Terms such as "first", "second", etc. in the specification, claims and the above-mentioned drawings of the present application are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence. It should be understood that such terms can be interchanged under appropriate circumstances, which is only a way of distinguishing when describing objects with the same attributes in the embodiments of the present application. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion, so that a process, method, system, product or device comprising a series of units does not have to be limited to those units, but may include other units not clearly listed or inherent to these processes, methods, products or devices.

[0039] As used herein, the terms "substantially", "about" and similar terms are used as approximate terms, rather than as terms of degree, and are intended to take into account the inherent deviations of measured or calculated values known to those of ordinary skill in the art. In addition, when describing the embodiments of the present invention, the use of "may" means "one or more possible embodiments". As used herein, the terms "use", "using" and "used" may be regarded as synonymous with the terms "utilize", "utilizing" and "utilized" respectively. Additionally, the term "exemplary" is intended to refer to an example or illustration.

[0040] Next, some concepts related to the present application will be described:

[0041] (1) Adapter: It refers to a device that supplies power to an electronic device (also known as a terminal device) with a voltage conversion function, and is also called a charging head, a switch power supply adapter, a charger, or a power converter.

[0042] (2) Super Charger: It refers to an adapter or charger that can achieve charging and can realize fast charging of battery-equipped devices such as mobile phones or computers, shortening the charging time. It is usually also called a Super Charger, an express charger, fast charging, quick charging, etc.

[0043] (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 secondary switching bridge is also called the auxiliary tube, the second switch, etc.

[0044] (4) Asymmetric half-bridge: In the present invention, it means that the duty cycles of the upper bridge and the lower bridge are not symmetrically turned on at 50%.

[0045] (5) Controller IC: It refers to the control unit of the product, which realizes waveform detection and action logic.

[0046] (6) Transformer: An element in a switching power supply that is responsible for power transmission and voltage conversion.

[0047] (7) Auxiliary winding: A winding in a transformer that is not responsible for power transmission, such as the VCC winding, etc.

[0048] (8) Primary winding: A winding in a transformer that is placed on the primary side and is responsible for input voltage and current.

[0049] (9) Secondary winding: A winding in a transformer that is placed on the secondary side and is responsible for output voltage and current.

[0050] To enable those skilled in the art to better understand the solution of the present application, the embodiments of the present application will be described below in conjunction with the accompanying drawings in the embodiments of the present application.

[0051] Figure 1 It is a schematic diagram of an active clamp circuit.

[0052] As Figure 1 shown, the embodiment of the present application provides an active clamp circuit. Among them, the active clamp circuit belongs to an active clamp flyback converter.

[0053] As Figure 1 shown, the active clamp flyback converter includes a transformer T1, and the transformer T1 includes a primary winding Np and a secondary winding Ns. On the output side of the transformer T1, that is, the secondary side, the active clamp flyback converter further includes an output voltage Vout ( Figure 1 abbreviated as V in 0 ) for characterizing the output and a corresponding output capacitor Cout ( Figure 1 abbreviated as C in 0 ), 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 by other types of rectifier tubes.

[0054] Due to the parasitic leakage inductance existing because the windings of transformer T1 cannot be ideally and tightly combined, the parasitic leakage inductance of transformer T1 is represented as an inductance Lr connected in series with the primary winding Np, and the inductance Lr should be understood as an inherent part of the primary winding Np. The moving and static points of the primary winding Np and the secondary winding Ns are relative concepts only for the convenience of explaining the reference directions of their respective induced electromotive forces, that is, the end where the moving point of the primary winding Np or the secondary winding Ns is located is relative to the other end where the static point is located.

[0055] On the input side of transformer T1, that is, the primary side, the active clamp flyback converter further includes an input voltage source Vin for characterizing the input, a corresponding input capacitor Cin, and a flyback circuit. Among them, the clamp circuit is connected to the primary winding Np of transformer T1 after being connected in parallel with the main power switch Q L in parallel.

[0056] Compared with the traditional flyback circuit, the active clamp circuit additionally adds a clamp switch tube and a clamp capacitor. Before the main power switch is turned on, the magnetizing inductor flows through currents in opposite directions. After the clamp switch tube is turned off, the negative current of the magnetizing inductor discharges the junction capacitance of the main power switch. When the voltage of the main power switch drops to 0, the main power switch is turned on, realizing ZVS turn-on and reducing switching losses.

[0057] However, during the turn-on period of the clamp switch tube, since the voltage of the clamp capacitor is higher than the reflected voltage of the secondary side of the transformer, it causes the SR on the secondary side to turn on, and the energy of the clamp capacitor is transferred to the output side through the transformer, resulting in a large current and thus a large loss problem.

[0058] To solve the above problems, the embodiment of the present application designs a flyback circuit.

[0059] Among them, the clamp circuit includes: a first energy storage element (such as Figure 1 the shown capacitor Cr), 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 (such as Figure 1 the shown capacitor C1). Among them, the flyback circuit can be connected in parallel at both ends of the main power switch Q L both ends.

[0060] In a possible implementation, the first branch further includes: a first diode D1. The first diode D1 is connected in series between the first energy storage element and the second energy storage element; the anode of the first diode D1 is connected to the first energy storage element, and the cathode of the first diode D1 is connected to the second energy storage element. The first diode D1 can block the reverse current relative to the first diode D1 from flowing to the first energy storage element.

[0061] In a possible implementation, the second branch includes an auxiliary switching transistor Q A and a second diode D2. The second diode D2 is connected in series between the first energy storage element and the auxiliary switching transistor Q A . The anode of the second diode D2 is connected to the auxiliary switching transistor Q A , and the cathode of the second diode D2 is connected to the first energy storage element. The second diode D2 can block the reverse current relative to the second diode D2 from flowing to the auxiliary switching transistor Q A .

[0062] In some exemplary embodiments, the first diode D1 and the second diode D2 can be implemented by suitable means in the prior art, such as point contact type, surface contact type or planar type diodes. These can be adjusted and improved according to the specific application environment, and no specific limitation is made here.

[0063] Among them, the auxiliary switching transistor is also called the upper transistor Q A , and the main power switching transistor is also called the lower transistor Q L . Optionally, the auxiliary switching transistor Q A and the main power switching transistor Q L are N-channel enhancement mode metal-oxide-semiconductor field-effect transistors (MOSFETs). The anodes of the parasitic diodes of the auxiliary switching transistor Q A and the main power switching transistor Q L are connected to the corresponding source electrodes, and the cathodes are connected to the corresponding drain electrodes. Among them, the input voltage source Vin is connected in series with the primary winding Np, and the main power switching transistor Q L is connected between the input voltage source Vin and the primary winding Np.

[0064] In a possible implementation, the first energy storage element and the second energy storage element are capacitors. For example, as shown in Figure 1 , the first energy storage element is a capacitor Cr, and the second energy storage element is a capacitor C1.

[0065] 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 Figure 4 , the first energy storage element is a capacitor Cr, and the second energy storage element is an auxiliary winding.

[0066] It should be understood that the number of elements included in the first energy storage element and the second energy storage element can be one or more, and when the number is multiple, the types of the elements can also be the same or different. The embodiments of the present application do not limit this.

[0067] Figure 1 The shown active clamp flyback converter can be used for complementary active clamp flyback and non - complementary active clamp flyback according to the control logic of the auxiliary switch tube Q A and the main power switch tube Q L . Among them, complementary active clamp flyback means that the driving waveforms of the upper main power switch tubes are complementary and there is a dead - time between them; non - complementary active clamp flyback means that the auxiliary switch tube Q A is only turned on for a short - time pulse, so that the main power switch tube Q L can achieve zero - voltage switching.

[0068] In a working state, the main power circuit on the primary side can be made conductive by controlling the turn - off and turn - on of the main power switch tube and the auxiliary switch tube. Next, the main power circuit will be introduced:

[0069] In a possible implementation, the clamping circuit further includes a controller. The controller is connected to the main power switch tube and the auxiliary switch tube, and the controller is configured to perform the following operations: switch the main power switch tube to the on state and switch the auxiliary switch tube to the off state, thereby allowing the current to flow through the main power circuit, where the main power circuit includes the primary winding and the main power switch tube.

[0070] Referring to Figure 2 , Figure 2 is the control signal schematic diagram of 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, switch the main power switch tube to the on state, thereby allowing the current to flow through the main power circuit, where 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 while 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 inductor Lr. That is, the input voltage source Vin magnetizes the excitation inductor of the transformer T1. At this time, the active clamp flyback converter includes a main power circuit. The main power circuit starts from the input voltage source Vin, and the input voltage successively passes through the input voltage source Vin, the primary winding Np (including the parasitic inductor Lr), the main power switch tube Q L , and finally returns to the input voltage source Vin.

[0071] In a working state, the clamping circuit of the flyback circuit can be made conductive by controlling the turn - off and turn - on of the main power switch tube and the auxiliary switch tube. Next, it will be introduced:

[0072] In a possible implementation, it can be in the first time period (for example Figure 2After t1), the main power switch tube is switched from the on state to the off state, and after the dead time, the auxiliary switch tube is switched from the off state to the on state, thereby allowing the 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, where the clamping circuit includes the primary winding, the first energy storage element and the second energy storage element.

[0073] In a possible implementation, the controller can control the main power switch tube Q L to turn off while the auxiliary switch tube Q A turns on, because when the main power switch tube Q L turns off, the input voltage is removed. The secondary winding Ns of the transformer T1 generates a reverse output voltage in the primary winding Np to maintain the magnetic flux unchanged. Specifically, the energy stored in the transformer (including the parasitic inductance L1) is transferred to the energy storage elements (the first energy storage element and the second energy storage element) of the clamping circuit for charging. At this time, the active clamp flyback converter includes a clamping circuit. The clamping circuit starts from the primary winding Np, and the reverse output voltage sequentially passes through the moving point of the primary winding Np, the first storage element (such as Figure 1 the capacitor Cr shown), the first diode D1, the second storage element (such as Figure 1 the capacitor C1 shown), the input voltage source Vin, and finally returns to the static point of the primary winding Np.

[0074] When the clamping circuit is conducting and the flyback circuit is in the forward charging state, the first energy storage element and the first branch conduct to form a clamping circuit; the first energy storage element and the second energy storage element absorb the leakage inductance energy of the primary winding through the clamping circuit. At this time, 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.

[0075] Referring to Figure 2 , Figure 2 is the control signal schematic diagram of the non-complementary active clamp flyback. At time t 1 , the exciting current reaches the preset value, the main power switch tube Q L is turned off, and after the dead time, the auxiliary switch tube Q A is turned on. At this time, the primary current of the transformer flows through the first energy storage element Cr and the second energy storage element C1. The two capacitors are connected in series, and the clamping voltage of the main power switch tube Q L is the sum of the voltages of the two capacitors.

[0076] In a working state, the reverse excitation circuit of the flyback circuit can be made to conduct by controlling the turn-off and turn-on of the main power switch tube Q L and the auxiliary switch tube Q A . The following is an introduction:

[0077] In a possible implementation, when the clamping circuit is in a state of charging the reverse excitation of the transformer, the first energy storage element and the second branch are turned on to form a reverse excitation loop.

[0078] In a possible implementation, switch the main power switch Q L to the off state and switch the auxiliary switch Q A to the on state, thereby allowing the current to flow through the reverse excitation loop and allowing the first energy storage element to charge the reverse excitation of the transformer through the reverse excitation loop (for example Figure 2 at time t3 in, where the time period between the auxiliary switch changing from the off state to the on state is the second time period), and the reverse excitation loop includes the first energy storage element, the primary winding, and the auxiliary switch Q A .

[0079] Referring to Figure 2 , Figure 2 is a schematic diagram of the control signal for non-complementary active clamp flyback. At time t 3 , turn on the auxiliary switch Q A , and the first energy storage element Cr gives reverse excitation to the excitation inductor, forming a negative current. Since when the clamping circuit is charging forward, the voltage across both ends is the sum of the voltages of the first energy storage element and the second energy storage element, and when discharging, it is only the voltage of the first energy storage element. When giving reverse excitation to the transformer, the excitation voltage is less than the reflected voltage of the secondary winding, so that the secondary SR will not turn on, thus eliminating the forward transfer of energy to the secondary side, thereby reducing the loss.

[0080] In this way, the active clamping circuit ensures that the excitation voltage generated on the secondary side of the transformer during the reverse excitation charging of the clamping element does not change the reverse cut-off state of the secondary rectifier tube, so that no spike current flows through the auxiliary switch tube and the secondary rectifier tube, effectively avoiding the problem of the forward transfer of excess energy to the secondary side of the transformer when the auxiliary switch tube is turned on.

[0081] The embodiments of the present application can be applied to application scenarios such as small power AC-DC power supplies, switching power supplies requiring high power density and high conversion efficiency, miniaturized high-efficiency power components, and consumer electronic products.

[0082] In a possible implementation, the controller is further configured to: based on the charging degree of the reverse excitation of the transformer by the first energy storage element, switch the main power switch tube to the on state to achieve zero voltage switching.

[0083] Referring to Figure 2 , Figure 2 is a schematic diagram of the control signal for non-complementary active clamp flyback. At time t4 At the moment when the auxiliary switch tube Q A is turned off, this negative current discharges the junction capacitance of the main power switch tube Q L ; at time t 5 , the Vds of the main power switch tube Q L drops to 0, and the main power switch tube Q L is turned on, achieving ZVS turn-on and reducing switching losses.

[0084] In addition, the embodiments of the present application can also be applied to complementary active-clamped flyback. For example, referring to Figure 3 , Figure 3 is a signal control schematic diagram of working in the critical conduction mode (CRM). As Figure 3 shown, except for leaving a switching dead zone, the main power switch tube Q L and the auxiliary switch tube Q A complementary conduct. The auxiliary switch tube Q A continues to conduct after the exciting current drops to 0, performs reverse excitation on the exciting inductor, forms a negative current, and creates conditions for realizing the soft switching of the main power switch tube Q L in the next stage.

[0085] In some exemplary embodiments, a switching power supply includes Figure 1 and Figure 3 the active-clamped circuit shown.

[0086] In addition, referring to Figure 5 , Figure 5 is a flow schematic diagram of a control method provided by the embodiments of the present application. This method can be applied to a controller in an active-clamped circuit (such as Figure 1 or Figure 4 the circuit introduced). The clamped circuit is connected to the primary winding of the transformer after being connected in parallel with the main power switch tube. The clamped 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;

[0087] The method includes:

[0088] 501. 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 the current flowing through the main power loop to flow, where the main power loop includes the primary winding and the main power switch tube;

[0089] 502. After a first time period of switching the main power switch to the on state, switch the main power switch from the on state to the off state, and after the dead time, switch the auxiliary switch from the off state to the on state, thereby allowing the 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;

[0090] In a possible implementation, the controller can control the main power switch Q L to turn off while the auxiliary switch Q A turns on, because when the main power switch Q L turns off, the input voltage is removed. The secondary winding Ns of the transformer T1 generates a reverse output voltage in the primary winding Np to maintain the magnetic flux unchanged. Specifically, the energy stored in the transformer (including the parasitic inductance L1) is transferred to the energy storage elements (the first energy storage element and the second energy storage element) of the clamping circuit for charging. At this time, the active clamp flyback converter includes a clamping circuit. The clamping circuit starts from the primary winding Np, and the reverse output voltage sequentially passes through the static point of the primary winding Np, the first storage element (such as Figure 1 the capacitor Cr shown), the first diode D1, the second storage element (such as Figure 1 the capacitor C1 shown), the input voltage source Vin, and finally returns to the moving point of the primary winding Np.

[0091] When the clamping circuit is conducting and the flyback circuit is in the forward charging state, the first energy storage element and the first branch conduct to form a clamping circuit; the first energy storage element and the second energy storage element 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 energy storage element and the second energy storage element.

[0092] 503. When the current flowing through the primary winding becomes 0, switch the auxiliary switch from the on state to the off state, and switch 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 perform reverse excitation charging on 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.

[0093] In a possible implementation, switch the main power switch Q L to the off state and switch the auxiliary switch Q Ato the conducting state, 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, where the reverse excitation circuit includes the first energy storage element, the primary winding, and the auxiliary switch tube Q A .

[0094] Referring Figure 2 , Figure 2 is a schematic diagram of the control signal for a non-complementary active clamp flyback. At time t 3 , turn on the auxiliary switch tube Q A , and the first energy storage element Cr reverse-excites the excitation inductor to form a negative current.

[0095] Since when the clamping circuit is charging forward, the voltage across both ends is the sum of the voltages of the first energy storage element and the second energy storage element, and when discharging, it is only the voltage of the first energy storage element. When reverse-exciting the transformer, the excitation voltage is less than the reflected voltage of the secondary winding, so that the secondary rectifier diode will not turn on, thus eliminating the positive excitation of energy to the secondary side, thereby reducing the loss.

[0096] In this way, the active clamping circuit ensures that the excitation voltage generated on the secondary side of the transformer when the clamping element reverse-excites and charges the transformer will not change the reverse cut-off state of the secondary rectifier diode, thus not causing a spike current to flow through the auxiliary switch tube and the secondary rectifier diode, effectively avoiding the problem of the transfer of excess energy to the secondary side of the transformer when the auxiliary switch tube is turned on instantaneously.

[0097] In one possible implementation, the method further includes:

[0098] Switch the main power switch tube to the conducting state and switch the auxiliary switch tube to the off state, thereby allowing current to flow through the main power circuit, where the main power circuit includes the primary winding and the main power switch tube;

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

[0100] Based on the charging degree of the reverse excitation of the transformer by the first energy storage element, switch the main power switch tube to the conducting state to achieve zero-voltage switching.

[0101] In one possible implementation, the first energy storage element is a capacitor, and the second energy storage element is a capacitor or a primary auxiliary winding.

[0102] In one possible implementation, when the clamping circuit is in the forward charging state, the first energy storage element and the first branch are turned on to form a clamping circuit; the first energy storage element and the second energy storage element absorb the leakage inductance energy of the primary winding through the clamping circuit.

[0103] In a possible implementation, when the clamping circuit is in a state of charging the reverse excitation of the transformer, the first energy storage element and the second branch are turned on to form a reverse excitation loop.

[0104] In a possible implementation, the first branch further includes: a first diode; the first diode is serially connected between the first energy storage element and the second energy storage element; the second branch further includes: a second diode, the second diode is serially connected between the first energy storage element and the auxiliary switch tube.

[0105] 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 the reverse current relative to the first diode from flowing to the first energy storage element.

[0106] 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 the reverse current relative to the second diode from flowing to the auxiliary switch tube.

[0107] 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.

[0108] The specific embodiments provided by the present application can be implemented by any one or a combination of hardware, software, firmware or solid-state logic circuits, and can be implemented in combination with signal processing, control and / or dedicated circuits. The devices or apparatuses provided by the specific embodiments of the present application may include one or more processors (for example, microprocessors, controllers, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), etc.), and these processors process various computer-executable instructions to control the operation of the devices or apparatuses. The devices or apparatuses provided by the specific embodiments of the present application may include a system bus or a data transmission system that connects the various components together. The system bus may include any one of different bus structures 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 a local bus using any one of a variety of bus architectures. The devices or apparatuses provided by the specific embodiments of the present application may be provided separately, may be a part of a system, or may be a part of other devices or apparatuses.

[0109] The specific embodiments provided by the present application may include a computer-readable storage medium 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, programs, and / or instructions, and when executed by the processor of the device or apparatus provided by the specific embodiment of the present application, these data, programs, and / or instructions cause these devices or apparatuses to implement related operations. The computer-readable storage medium / storage device may include one or more of the following features: volatile, non-volatile, dynamic, static, readable / writable, read-only, random access, sequential access, location-addressable, file-addressable, and content-addressable. In one or more exemplary embodiments, the computer-readable storage medium / storage device may be integrated into the device or apparatus provided by the specific embodiment of the present application or belong to a common system. The computer-readable storage medium / storage device 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 optical discs (CDs), digital versatile discs (DVDs), mass storage media devices, or any other suitable form of storage medium.

[0110] The above are the implementation manners of the embodiments of the present application. It should be noted that the steps in the methods described in the specific embodiments of the present application can be adjusted, combined, and deleted according to actual needs. In the above embodiments, the descriptions of each embodiment have their own focuses. For the parts not detailedly described in a certain embodiment, reference can be made to the relevant descriptions of other embodiments. It can be understood 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 the drawings, or combine certain components, or split certain components, or have different component arrangements. Those skilled in the art will understand that various modifications or changes can be made to the arrangements, operations, and details of the methods and devices described in the specific embodiments without departing from the spirit and scope of the specific embodiments of the present application; without departing from the principle of the embodiments of the present application, several improvements and refinements can also be made, and these improvements and refinements are also regarded as the protection scope of the present application.

Claims

1. An active clamp circuit, characterized in that, the clamp circuit is connected in parallel with the main power switch and then connected to the primary winding of the transformer, and the clamp 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; wherein, the first energy storage element and the first branch are turned on to form a clamping loop, and after the main power switch 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 loop, the first energy storage element discharges when the auxiliary switch is turned on to charge the reverse excitation of the transformer.

2. The active clamp 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, the second diode is connected in series between the first energy storage element and the auxiliary switch.

3. The active clamp circuit according to claim 2, characterized in that, 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 release of energy from the first energy storage element.

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

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

6. The active clamp circuit according to any one of claims 1 to 5, characterized in that, the clamp circuit further includes a controller, the controller is connected to the main power switch and the auxiliary switch, and the controller is configured to sequentially perform the following operations: 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 the current to flow through the main power loop, wherein the main power loop includes the primary winding and the main power switch; After a first time period of switching the main power switch to the on state, switch the main power switch from the on state to the off state, and after the dead time, switch the auxiliary switch 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, switch the auxiliary switch 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 perform reverse excitation charging on the transformer through the reverse excitation circuit, and the reverse excitation circuit includes the first energy storage element, the primary winding, and the auxiliary switch.

7. The active clamping circuit according to claim 6, wherein, the controller is further configured to: Based on the charging degree of the reverse excitation of the transformer by the first energy storage element, switch the main power switch to the on state to achieve zero voltage switching.

8. The active clamping circuit according to any one of claims 1-7, wherein, 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, 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 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; the controller is connected to the main power switch and the auxiliary switch; the method includes: 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 the main power circuit, wherein the main power circuit includes the primary winding and the main power switch; After a first time period of switching the main power switch to the on state, switch the main power switch from the on state to the off state, and after the dead time, switch the auxiliary switch 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, switch the auxiliary switch transistor from the on state to the off state, and after a second time period, switch it to the on state, thereby allowing the current to flow through the reverse excitation circuit and allowing the first energy storage element to perform reverse excitation charging of the transformer through the reverse excitation circuit. The reverse excitation circuit includes the first energy storage element, the primary winding, and the auxiliary switch transistor.

10. An active clamp flyback converter, characterized in that it includes: the active clamp circuit as described in any one of claims 1-8 and a transformer; the clamp circuit is connected to the primary winding of the transformer after being connected in parallel with the main power switch transistor.

11. A switching power supply, characterized in that the switching power supply includes the active clamp circuit as described in any one of claims 1-8.

Images