Circuit that realizes ZVS for flyback switching power supply using auxiliary winding

Abstract

To provide a circuit capable of achieving a zero-voltage soft switching (ZVS) of a flyback switching power supply by using auxiliary winding.SOLUTION: In a circuit, a ZVS capacitor C2 and a ZVS switching module Qa are increased, one end of the ZVS capacitor C2 and a different electrode end of an auxiliary winding W are connected to a first node Vaux, a control circuit generates a ZVS control signal on the basis of a first node voltage before a primary side power switch Qp is energized, and energizes the ZVS switching module Qa, and a resonance current is formed among the auxiliary winding W, the ZVS capacitor C2, and the ZVS switching module Qa. At the same time, an inverse of an excited current of a primary side winding is realized by a magnetic coupling between the auxiliary winding W and a transformer T, a coupling capacity electric charge of the primary side power switch Qp is inversely extracted. Thereby, a Vds voltage of the primary side power switch Qp is reduced to zero, the ZVS of the primary side power switch Qp is realized, and an operation efficiency of a flyback power supply system can be improved.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present application relates to the field of switching power supplies, and more particularly to a circuit that realizes ZVS in a flyback switching power supply by utilizing an auxiliary winding. [Background technology]

[0002] In flyback power supplies, the traditional quasi-resonant flyback (QR) mode or continuous conduction (CCM) mode often does not operate efficiently when supplying power to many high power loads. Now, the Zero Voltage Switch (ZVS) technology can be used to improve the operating efficiency of flyback power supply systems.

[0003] Among them, the operating principle of ZVS technology is that the voltage (Vds) between the drain and source electrodes of the main power switch transistor (MOSFET transistor) on the primary side of the transformer is reduced to zero before the MOSFET transistor is turned on.

[0004] When using ZVS technology in a flyback power supply, adding an independent auxiliary winding on the primary side of the transformer realizes the reversal of the excitation current on the primary side of the transformer, thereby back-extracting the coupling capacitance charge of the MOSFET transistor and lowering the Vds voltage to zero before the MOSFET transistor conducts, thereby realizing ZVS and improving the operating efficiency of the flyback power supply system. However, the method of adding an extra auxiliary winding not only increases the cost, but also increases the complexity of creating the transformer winding and the complexity of controlling the primary side circuit, reducing the reliability of the product.

[0005] From this, it can be seen that how to realize the ZVS function of a flyback switching power supply and improve the operation efficiency of the system while reducing the cost is a problem that needs to be solved immediately by those skilled in the art. Summary of the Invention

[0006] An object of the present application is to provide a circuit that realizes ZVS of a flyback switching power supply by utilizing an auxiliary winding, in order to improve the operating efficiency of the flyback switching power supply by realizing ZVS of the flyback switching power supply.

[0007] In order to solve the above technical problems, the present application provides a circuit that realizes ZVS of a flyback switching power supply by using an auxiliary winding, a transformer having a primary winding, a secondary winding, and an auxiliary winding; a power switch coupled to the same pole of the primary winding and controlled by a control circuit of the switching power supply; a ZVS switching module, a first end of which is connected to one end of a ZVS capacitor, the other end of the ZVS capacitor and the opposite pole end of the auxiliary winding are connected to a first node, the same pole end of the auxiliary winding and a second end of the ZVS switching module are respectively grounded, and the control circuit generates a ZVS control signal based on a voltage at the first node, and controls the ZVS switching module by the control end of the ZVS switching module, thereby realizing ZVS of the power switch.

[0008] Preferably, the ZVS switching module is a field effect transistor; The first terminal of the field effect transistor is a connection terminal connected to one terminal of the ZVS capacitor, the second terminal is grounded, and the control terminal is connected to the ZVS control terminal of the control circuit.

[0009] Preferably, the circuit for achieving ZVS of a flyback switching power supply by using the auxiliary winding further includes a first resistor and a second resistor, The first resistor and the second resistor are connected in series, and a common terminal is connected to a voltage sampling terminal of the control circuit, the other terminal of the first resistor is connected to the positive electrode of the first diode, and the other terminal of the second resistor is grounded.

[0010] Preferably, the circuit for achieving ZVS of a flyback switching power supply by using the auxiliary winding further includes a first diode and a first capacitor; A common end generated by connecting the negative electrode of the first diode and one end of the first capacitor is connected to a power supply end of the control circuit, the other end of the first capacitor is grounded, and the positive electrode of the first diode is connected to the opposite pole of the auxiliary winding. When the power switch is turned on, the auxiliary winding, the first diode and the first capacitor form an energy storage circuit to charge the first capacitor, making it easier for the first capacitor to supply power to the control circuit.

[0011] In order to solve the above technical problems, the present application further provides a flyback switching power supply including a circuit for achieving ZVS of the flyback switching power supply by utilizing the auxiliary winding.

[0012] The circuit for achieving ZVS of a flyback switching power supply using an auxiliary winding provided in the present application is based on the auxiliary winding inherent in the transformer, and adds a ZVS capacitor and a ZVS switching module, and connects one end of the ZVS capacitor and the opposite end of the auxiliary winding to a first node, and before the primary side power switch is turned on, a control circuit generates a ZVS control signal according to the voltage of the first node to turn on the ZVS switching module, and forms a resonant current between the auxiliary winding, the ZVS capacitor and the ZVS switching module, and the resonant current affects the voltage of the primary side power switch to generate a downward resonance. At the same time, the magnetic coupling between the auxiliary winding and the transformer realizes the reversal of the excitation current of the primary side winding, and reversely extracts the coupling capacitance charge of the primary side power switch, thereby reducing the Vds voltage of the primary side power switch to zero, thereby achieving ZVS of the primary side power switch, avoiding the high cost caused by adding a separate auxiliary winding to the primary side of the transformer, and improving the operating efficiency of the flyback power supply system.

[0013] Furthermore, the present application also provides a flyback switching power supply corresponding to a circuit that realizes ZVS of a flyback switching power supply by utilizing the above-mentioned auxiliary winding, and has the same effect.

[0014] In order to more clearly explain the embodiments of the present application, the following provides a brief introduction of drawings that may be used in the embodiments. However, the drawings in the following description are only some of the embodiments of the present application, and it is obvious that a person skilled in the art can obtain other drawings based on these drawings on the premise that no creative work is performed. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram of a circuit for achieving ZVS of a flyback switching power supply using an auxiliary winding provided in an embodiment of the present application. [Diagram 2] FIG. 2 is a schematic diagram of a circuit for achieving ZVS of a flyback switching power supply by using an auxiliary winding provided in another embodiment of the present application. [Diagram 3] FIG. 2 is a voltage waveform diagram of a circuit for achieving ZVS of a flyback switching power supply by using an auxiliary winding, provided in an embodiment of the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The technical methods in the embodiments of the present application will be described below clearly and completely in conjunction with the drawings in the embodiments of the present application, but it is clear that the described embodiments are only a part of the embodiments of the present application, and are not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without performing creative labor, fall within the scope of protection of the present application.

[0017] The gist of this application is to provide a circuit that uses an auxiliary winding to achieve ZVS in a flyback switching power supply. Based on the original auxiliary winding, a ZVS capacitor and a ZVS switching module are added. The resonant current formed by the auxiliary winding, the ZVS capacitor, and the ZVS switching module affects the power switch to produce downward resonance, and at the same time, the excitation coupling between the transformer and the auxiliary winding reverses the excitation current of the primary winding to reversely extract the coupling capacitance of the primary power switch, thereby achieving ZVS in the flyback switching power supply and improving the operating efficiency of the system.

[0018] In order to allow those skilled in the art to better understand the present invention, the present invention will be described in more detail below in conjunction with drawings and specific embodiments.

[0019] In flyback power supplies, the traditional quasi-resonant flyback (QR) mode or continuous conduction (CCM) mode often have low operating efficiency when supplying power to many high power loads. Currently, the ZVS technique can be used to improve the operating efficiency of flyback power supply systems.

[0020] Among them, the operating principle of ZVS technology is that the voltage (Vds) between the drain and source electrodes of the main power switch transistor (MOSFET transistor) on the primary side of the transformer is reduced to zero before the MOSFET transistor is turned on.

[0021] When using ZVS technology in a flyback power supply, adding an independent auxiliary winding on the primary side of the transformer realizes the reversal of the primary excitation current of the transformer, thereby back-extracting the coupling capacitance charge of the MOSFET transistor and lowering the Vds voltage to zero before the MOSFET transistor conducts, thereby realizing ZVS and improving the operating efficiency of the flyback power supply system. However, the method of adding an extra auxiliary winding not only increases the cost, but also increases the complexity of creating the transformer winding and the complexity of controlling the primary circuit, which reduces the reliability of the product.

[0022] In order to reduce costs and at the same time realize the ZVS function of the flyback switching power supply and improve the operating efficiency of the flyback power supply system, the present application provides a circuit that realizes ZVS of the flyback switching power supply by using an auxiliary winding, and adds a ZVS switching module and a ZVS capacitor to the auxiliary winding technology inherent in the transformer, connects the control end of the ZVS switching module to the ZVS control end of the control circuit, and before the primary side power switch is turned on, the control circuit controls the conduction of the ZVS switching module to generate a resonant current between the auxiliary winding, the ZVS switching module, and the ZVS capacitor, which causes downward resonance in the power switch, and at the same time, realizes excitation and reverse extraction of the coupling capacitance charge of the power switch by the auxiliary winding and the transformer, thereby realizing ZVS of the power switch.

[0023] 1 is a schematic diagram of a circuit for implementing ZVS in a flyback switching power supply using an auxiliary winding provided in an embodiment of the present application. As shown in FIG. 1, the circuit includes a transformer T, a power switch Qp, a ZVS switching module Qa, and a ZVS capacitor C2. The transformer T has a primary winding, a secondary winding, and an auxiliary winding W, and the power switch Qp is coupled to the same pole of the primary winding and controlled by a control terminal gate of a control circuit. A first terminal of the ZVS switching module Qa and one terminal of the ZVS capacitor C2 are connected to a node Vsw, the other terminal of the ZVS capacitor C2 and the opposite pole of the auxiliary winding W are connected to a first node Vaux, and the same pole of the auxiliary winding W and the second terminal of the ZVS switching module Qa are grounded respectively.

[0024] In practice, before the power switch Qp is turned on, the control circuit generates a ZVS control signal based on the voltage of the first node Vaux to turn on the ZVS switching module Qa. At this time, a ground current is formed between the auxiliary winding W, the ZVS capacitor C2 and the ZVS switching module Qa, which affects the voltage of the power switch Qp and generates downward resonance. At the same time, the excitation coupling generated between the auxiliary winding W and the transformer T causes the excitation current of the primary winding to reversely extract the coupling capacitance charge of the power switch Qp, thereby realizing ZVS of the power switch Qp. That is, ZVS of the flyback switching power supply is realized.

[0025] In implementation, the control circuit, by sampling the voltage difference of the auxiliary winding, through some stepwise trial and error algorithm, determines the appropriate conduction time of the ZVS switching module Qa, thereby realizing the optimal ZVS of the system, i.e., maximizing the operating efficiency of the system.

[0026] The circuit for achieving ZVS of a flyback switching power supply using an auxiliary winding provided in the embodiment of the present application is based on the auxiliary winding inherent in the transformer, and adds a ZVS capacitor and a ZVS switching module, and connects one end of the ZVS capacitor and the opposite end of the auxiliary winding to a first node. Before the primary power switch is turned on, a control circuit generates a ZVS control signal according to the voltage of the first node to turn on the ZVS switching module, and forms a resonant current between the auxiliary winding, the ZVS capacitor, and the ZVS switching module. The resonant current affects the voltage of the primary power switch, causing a downward resonance. At the same time, the magnetic coupling between the auxiliary winding and the transformer realizes the reversal of the excitation current of the primary winding, and reverses the coupling capacitance charge of the primary power switch, thereby reducing the Vds voltage of the primary power switch to zero, thereby achieving ZVS of the primary power switch, avoiding the high cost caused by adding a separate auxiliary winding to the primary side of the transformer, and improving the operating efficiency of the flyback power supply system.

[0027] 2 is a schematic diagram of a circuit for achieving ZVS of a flyback switching power supply by using an auxiliary winding provided in another embodiment of the present application, in a specific embodiment, the ZVS switching module may be a field effect transistor, or a diode and a triode connected in parallel, and the present application is not limited thereto. The field effect transistor has its own parasitic diode and is easy to use, so the field effect transistor is preferred.

[0028] When the ZVS switching module is a field effect transistor, as shown in Fig. 2, the first end of the field effect transistor Qa is a connection end connected to one end of the ZVS capacitor C2, the second end is grounded, and the control end is connected to the control end ZVS_DR of the control circuit. The control circuit generates a ZVS control signal according to the voltage of the first node Vaux, and controls the field effect transistor Qa to conduct before the power switch Qp conducts, thereby forming a resonant current between the auxiliary winding W, the ZVS capacitor C2, and the field effect transistor Qa, and making it easier to realize ZVS for the power switch Qp.

[0029] The circuit provided in the embodiment of the present application for achieving ZVS in a flyback switching power supply using an auxiliary winding uses a ZVS switching module as a field effect transistor to ensure the realization of ZVS in the flyback switching power supply, and is simple to design and easy to use.

[0030] As a preferred embodiment, as shown in FIG. 2, the circuit for achieving ZVS of a flyback switching power supply by using an auxiliary winding provided in the present application further includes a first resistor R1 and a second resistor R2, the first resistor R1 and the second resistor R2 are connected in series, and the common end is connected to a voltage sampling end DEM of a control circuit, the other end of the first resistor R1 is connected to the opposite pole of the auxiliary winding W, and the other end of the second resistor R2 is grounded.

[0031] In implementation, the control circuit utilizes the first resistor R1 and the second resistor R2 to realize voltage division sampling for the opposite polarity voltage Vaux of the auxiliary winding W, and generates a ZVS control signal to control the on and off of the ZVS switching module Qa, thereby realizing ZVS of the power switch Qp.

[0032] 3 is a voltage waveform diagram of a circuit that realizes ZVS of a flyback switching power supply using an auxiliary winding provided in an embodiment of the present application, and as shown in FIG. 3, the Vaux platform negative voltage represents the power voltage Vout of the switching power supply, the platform positive voltage represents the input voltage Vin of the switching power supply, and the Vaux resonant waveform can represent the bottom. That is, in this embodiment, information such as the input voltage Vin, the power voltage Vout, and the resonant bottom can be detected by simply sampling Vaux. In addition, when a resistive voltage divider is used, the withstand voltage of the voltage sampling end DEM of the control circuit can be 5V.

[0033] The circuit for realizing ZVS of a flyback switching power supply using an auxiliary winding provided in the embodiments of the present application adds a first resistor and a second resistor to realize voltage division sampling of opposite poles of the auxiliary winding, thereby generating a ZVS control signal to realize ZVS of the power switch.

[0034] Based on the above embodiment, the present application provides a circuit for achieving ZVS of a flyback switching power supply by using an auxiliary winding, which further includes a first diode D1 and a first capacitor C1. As shown in FIG. 2, the common terminal formed by connecting the negative terminal of the first diode D1 and one end of the first capacitor C1 is connected to the power supply terminal of the control circuit, the other end of the first capacitor C1 is grounded, and the positive terminal of the first diode D1 is connected to the opposite pole of the auxiliary winding. When the power switch is turned on, the auxiliary winding, the first diode D1 and the first capacitor C1 form an energy storage circuit to charge the first capacitor C1, so that the first capacitor C1 can easily supply power to the control circuit.

[0035] In practice, when the power switch Qp is turned off, the auxiliary winding W, the ZVS capacitor C2 and the ZVS switching module Qa form a flyback energy storage circuit, which charges and stores energy for the ZVS capacitor C2. When the power switch Qp is turned on, the auxiliary winding W, the first diode D1 and the first capacitor C1 form a forward energy storage circuit, which charges and stores energy for the first capacitor C1. At this time, in the forward state where the control circuit is supplied with power, the electric energy stored in the ZVS capacitor C2 in the flyback and the electric energy stored in the first capacitor C1 in the forward state are combined to supply power to the control circuit VCC terminal, thereby reducing the loss at the control circuit VCC terminal.

[0036] In other words, the present application uses the same auxiliary winding to jointly realize ZVS of the flyback switching power supply and realize the power supply function for the control circuit, that is, the same transformer auxiliary winding is used to reduce the complexity of the auxiliary winding and circuit design, thereby reducing the manufacturing cost of the entire power supply.

[0037] The circuit for realizing ZVS of a flyback switching power supply using an auxiliary winding provided in the embodiment of the present application connects a common terminal generated by connecting a first diode and a first capacitor in series to the power supply terminal of a control circuit, and connects the positive pole of the first diode to an auxiliary winding. In this way, the technical method provided in the present application can not only realize power supply to the control circuit, but also realize ZVS of the flyback switching power supply, thereby improving the operating efficiency and reliability of the system.

[0038] In the above embodiment, a circuit for realizing ZVS of a flyback switching power supply by using an auxiliary winding is described in detail. In the embodiment of the present application, a flyback switching power supply including the above circuit for realizing ZVS of a flyback switching power supply by using an auxiliary winding is further provided. The beneficial effects produced correspond to those of the circuit for realizing ZVS of a flyback switching power supply by using an auxiliary winding, and the effects are the same, so they will not be repeated here.

[0039] As described above, the circuit for achieving ZVS of a flyback switching power supply using the auxiliary winding provided in the present application has been introduced in detail. Each embodiment of the specification is described in a progressive manner, but the key points of the description of each embodiment are different from other embodiments, and the same or similar parts between the embodiments can be cross-referenced. The apparatus disclosed in the embodiments corresponds to the method disclosed in the embodiments and is relatively simply described, so that the relevant points can be referred to the description of the method part. It is pointed out that a person skilled in the art can make some improvements and modifications to the present application without departing from the principle of the present application, and such improvements and modifications are also included in the scope of the claims of the present application.

[0040] It should also be explained that relational terms such as first, second, etc. are used herein only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any substantial relationship or sequence between those entities or operations. Also, the terms "comprise," "include," or any other variation thereof cover non-exclusive inclusions, such that a process, method, article, or installation that includes a set of elements includes not only those elements, but also other elements not expressly listed or elements inherent to that type of process, method, article, or installation. Unless more restrictive, an element qualified by the phrase "including a..." does not exclude the presence of additional identical elements in the process, method, article, or installation that includes that element.

Claims

1. In a circuit that realizes ZVS of a flyback switching power supply using an auxiliary winding, a transformer having a primary winding, a secondary winding, and an auxiliary winding; a power switch coupled to the same pole of the primary winding and controlled by a control circuit of the flyback switching power supply; a ZVS switching module, a first end of which is connected to one end of a ZVS capacitor, the other end of the ZVS capacitor and the opposite pole end of the auxiliary winding are connected to a first node, and the same pole end of the auxiliary winding and a second end of the ZVS switching module are respectively grounded, the control circuit generates a ZVS control signal according to a voltage at the first node, and controls the ZVS switching module through the control end of the ZVS switching module, thereby realizing ZVS of the power switch; a first diode and a first capacitor; a common terminal generated by connecting a negative electrode of the first diode and one end of the first capacitor is connected to a power supply terminal of the control circuit, the other end of the first capacitor is grounded, and a positive electrode of the first diode is connected to a different pole of the auxiliary winding; when the power switch is turned on, the auxiliary winding, the first diode, and the first capacitor form an energy storage circuit to charge the first capacitor, thereby making it easier for the first capacitor to supply power to the control circuit. A circuit that realizes ZVS for a flyback switching power supply by using an auxiliary winding.

2. The ZVS switching module is a field effect transistor; a first end of the field effect transistor is a connection end connected to one end of the ZVS capacitor, a second end of the field effect transistor is grounded, and a control end of the field effect transistor is connected to a ZVS control end of the control circuit; A circuit for realizing ZVS of a flyback switching power supply by utilizing the auxiliary winding according to claim 1.

3. further comprising a first resistor and a second resistor; the first resistor and the second resistor are connected in series, and a common terminal is connected to a voltage sampling terminal of the control circuit, the other terminal of the first resistor is connected to a different pole terminal of the auxiliary winding, and the other terminal of the second resistor is grounded. A circuit for realizing ZVS of a flyback switching power supply by utilizing the auxiliary winding according to claim 2.

4. A flyback switching power supply comprising a circuit for realizing ZVS of the flyback switching power supply by utilizing the auxiliary winding according to any one of claims 1 to 3.

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