A soft switching device of a switching power supply, a switching power supply and a control method thereof

Abstract

The application discloses a soft switching device of a switching power supply, the switching power supply and a control method thereof. The device comprises a transformer and a switching tube. The transformer has a primary winding and a secondary winding. The primary winding comprises a first winding. A power supply bus of the switching power supply is connected to the same name end of the first winding. The different name end of the first winding is connected to the first connection end of the switching tube. The second connection end of the switching tube is grounded. The secondary winding is output to a load. The first connection end of the switching tube is connected to the second connection end of the switching tube through an absorption unit and a resonance unit, forming a resonance absorption loop. In the case that the switching tube is turned off, the leakage energy of the transformer is absorbed at the switching tube turn-off moment and resonance is performed, so that the peak voltage of the switching tube is reduced when the switching tube is turned on in the next period, and soft switching of the switching tube is realized. According to the scheme, the soft switching of the switching tube is realized by using the energy of the leakage inductance in the switching power supply, and the turn-on loss and turn-off loss of the switching power supply are reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of switching power supply, and particularly relates to a soft switching device of a switching power supply, the switching power supply and a control method thereof, in particular to a soft switching circuit of a novel low-loss power supply topology, a switching power supply (such as a flyback isolated switching power supply) with the soft switching circuit of the novel low-loss power supply topology, and a control method of the switching power supply. BACKGROUND

[0002] In the design process of the switching power supply, the control of the loss needs to be particularly paid attention to, and the loss of the switching power supply mainly includes turn-on loss, conduction loss and turn-off loss. In the related scheme, in the topology of the switching power supply (such as a flyback switching power supply) for small power applications, a hard switching mode is still adopted, that is, the switching tube is turned on given the driving signal, and at the turn-on moment or the turn-off moment, the platform voltage caused by the Miller capacitor leads to the loss caused by the included angle between the voltage and the current, resulting in large turn-on loss and turn-off loss of the switching power supply.

[0003] The above content is only used to assist in understanding the technical solutions of the present application and does not represent the acknowledgement of the above content as prior art. SUMMARY

[0004] The purpose of the present application is to provide a soft switching device of a switching power supply, the switching power supply and a control method thereof, so as to solve the problem that the switching power supply adopts a hard switching mode to control the turn-on or turn-off of the switching tube, at the turn-on moment or the turn-off moment of the switching tube, the platform voltage caused by the Miller capacitor leads to the loss caused by the included angle between the voltage and the current, resulting in large turn-on loss and turn-off loss of the switching power supply, so as to achieve the effect of realizing the soft switching of the switching tube by utilizing the energy of the leakage inductance in the switching power supply, and reducing the turn-on loss and turn-off loss of the switching power supply.

[0005] The present application provides a soft switching device of a switching power supply, the switching power supply comprising: a transformer and a switching tube, the transformer having a primary winding and a secondary winding, the primary winding comprising a first winding; a power supply bus of the switching power supply connected to the same name end of the first winding; the opposite name end of the first winding connected to the first connection end of the switching tube, the second connection end of the switching tube grounded; the secondary winding output to a load; the soft switching device of the switching power supply comprising: an absorption unit and a resonance unit; wherein the first connection end of the switching tube is connected to the second connection end of the switching tube through the absorption unit and the resonance unit, forming a resonance absorption loop, so as to absorb the leakage energy of the transformer at the moment of turn-off of the switching tube and resonate in the case of turn-off of the switching tube, so as to reduce the peak voltage of the switching tube at the turn-on moment of the next cycle, and realize the soft switching of the switching tube.

[0006] In some embodiments, the switch tube is a MOS tube, the first connection end of the switch tube is the drain of the MOS tube, and the second connection end of the switch tube is the source of the MOS tube.

[0007] In some embodiments, the absorption unit comprises a first diode module and a first capacitor module; the opposite name end of the first winding is connected to the anode of the first diode module; the cathode of the first diode module is connected to the second connection end of the first capacitor module; the first connection end of the first capacitor module is connected to the first connection end of the resonance unit; the second connection end of the resonance unit is connected to the second connection end of the first capacitor module; and the second connection end of the resonance unit is also connected to the second connection end of the switch tube.

[0008] In some embodiments, the soft switching device of the switching power supply further comprises a second diode module; the second connection end of the first capacitor module is connected to the anode of the second diode module; and the cathode of the second diode module is connected to the second connection end of the resonance unit.

[0009] In some embodiments, the soft switching device of the switching power supply further comprises a third diode module; the first connection end of the first capacitor module is connected to the cathode of the third diode module; and the anode of the third diode module is connected to the first connection end of the resonance unit.

[0010] In some embodiments, the resonance unit comprises an inductor module and a second capacitor module; the inductor module and the second capacitor module are connected in parallel to form an LC resonance circuit; the first connection end of the LC resonance circuit is the first connection end of the resonance unit; and the second connection end of the LC resonance circuit is the second connection end of the resonance unit, which is connected to the second connection end of the switch tube.

[0011] In order to match the above device, the present application further provides a switching power supply comprising the above soft switching device of the switching power supply.

[0012] In another aspect, the application provides a control method of a switching power supply, comprising: obtaining a voltage reflected from a secondary winding of the transformer to a primary winding, denoted as a reflected voltage; obtaining a leakage voltage of the transformer; determining parameters of components in the absorption unit and the resonance unit according to the reflected voltage and the leakage voltage; setting the components in the absorption unit and the resonance unit according to the parameters of the components in the absorption unit and the resonance unit; in the case that the switching tube is turned on, the primary winding of the transformer receives a bus voltage of the power bus to store energy; in the case that the switching tube is turned off, the primary winding of the transformer releases energy to the resonance absorption circuit; at the moment that the switching tube is turned off, the resonance absorption circuit absorbs leakage energy generated by the leakage voltage of the transformer and resonates, so that the peak voltage of the switching tube is reduced when the switching tube is turned on in the next cycle, and the soft switching of the switching tube is realized.

[0013] In some embodiments, the method further comprises: obtaining a bus voltage of the power bus, obtaining a current between the first connection end of the switching tube and the second connection end of the switching tube, and obtaining an output voltage of the secondary winding; determining a duty cycle signal of the control end of the switching tube according to the bus voltage of the power bus, the current between the first connection end of the switching tube and the second connection end of the switching tube, and the output voltage of the secondary winding; and controlling the turning on or turning off of the switching tube according to the duty cycle signal of the control end of the switching tube.

[0014] Therefore, by using the RCD circuit of the switching power supply (such as the flyback isolation switching power supply), the RCD circuit is composed of a resistance module, a capacitor module (such as the capacitor C1) and a diode module (such as the diode D1), the LC resonance circuit is arranged to replace the resistance module in the RCD circuit, the leakage voltage of the transformer T in the switching power supply is used to supply power to the LC resonance circuit, the resonance of the resonance circuit is realized to reduce the turn-on loss and the turn-off loss of the switching tube (such as the MOS tube M1) in the switching power supply, and thus the soft switching of the switching tube is realized by using the energy of the leakage in the switching power supply, and the turn-on loss and the turn-off loss of the switching power supply are reduced.

[0015] Other features and advantages of the application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the application.

[0016] The technical solutions of the application will be further described in detail below with reference to the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 FIG. 1 is a structural schematic diagram of an embodiment of the soft switching device of the switching power supply of the application.

[0018] Figure 2 A structural schematic diagram of an embodiment of a soft switching circuit of a novel low-loss power supply topology of the present application, specifically a modified flyback power supply topology diagram;

[0019] Figure 3 A flowchart of an embodiment of the control method of the present application;

[0020] Figure 4 A flowchart of an embodiment of the duty cycle signal for controlling the switching tube in the method of the present application.

[0021] Figure 5 A flowchart of an embodiment of the control method of a soft switching circuit of a novel low-loss power supply topology of the present application;

[0022] Figure 6 A working flowchart of a PI controller. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with specific embodiments of the present application and corresponding drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0024] It is considered that the switching power supply adopts a hard switching mode to control the turn-on or turn-off of the switching tube (such as a MOS tube), and at the turn-on time or turn-off time of the switching tube, the platform voltage caused by the Miller capacitor leads to the generation of loss due to the included angle between the voltage and the current, resulting in large turn-on loss and turn-off loss of the switching power supply. Moreover, the high turn-off voltage of the MOSFET (i.e. MOS tube) at the turn-off moment is coupled to the Miller capacitor, causing the driving voltage of the MOS tube to oscillate and heat during the driving voltage platform period, and even posing a risk of damaging the MOS tube. In addition, the energy of the leakage inductance in the switching power supply is only released by the RCD (i.e. residual current device) circuit as useless work, causing energy waste. coupled to the voltage, causing the driving voltage of the MOS tube to oscillate and heat during the driving voltage platform period, and even posing a risk of damaging the MOS tube. In addition, the energy of the leakage inductance in the switching power supply is only released by the RCD (i.e. residual current device) circuit as useless work, causing energy waste.

[0025] And for the conduction loss of the switching power supply, once the MOSFET (MOS tube) is selected, the conduction loss of the switching power supply is only determined by the effective current flowing through the MOS tube and the equivalent internal resistance of the MOSFET, so the conduction loss of the switching power supply is a value that cannot be changed. Therefore, in order to reduce the loss of the switching power supply, only the turn-on loss and the turn-off loss of the switching power supply can be reduced, and the leakage energy of the switching power supply is often wasted as useless work. Therefore, the scheme of the present application proposes a technical scheme for realizing soft switching of switching power supply by using leakage voltage, specifically a soft switching circuit of a new low-loss power supply topology and a switching circuit control scheme, to realize soft switching of the switching tube by using the energy of the leakage inductance in the switching power supply, thereby reducing the turn-on loss and the turn-off loss of the switching power supply.

[0026] According to an embodiment of the present application, a soft switching device of a switching power supply is provided. Referring to Figure 1 The switching power supply includes a transformer and a switching tube, the transformer has a primary winding and a secondary winding, the primary winding includes a first winding; a power supply bus of the switching power supply is connected to the same end of the first winding; the opposite end of the first winding is connected to the first connection end (such as the drain of MOS tube M1) of the switching tube, and the second connection end (such as the source of MOS tube M1) of the switching tube is grounded; the secondary winding is output to a load. The soft switching device of the switching power supply includes an absorption unit and a resonance unit, the absorption unit is an absorption circuit composed of a capacitor C1 and a diode D1, and the resonance unit is an LC resonance circuit.

[0027] The first connection end of the switching tube is connected to the second connection end of the switching tube through the absorption unit and the resonance unit, forming a resonance absorption loop, to absorb the leakage energy of the transformer at the moment of switching off of the switching tube and resonate, so that the peak voltage of the switching tube is reduced when the switching tube is turned on in the next cycle, realizing soft switching of the switching tube, reducing the turn-on loss and the turn-off loss of the switching power supply, and improving the utilization rate of the leakage energy of the transformer in the switching power supply.

[0028] The soft switching circuit of a new low-loss power supply topology proposed by the scheme of the present application uses the often wasted leakage voltage to provide a resonance network and realize soft switching of the switching power supply, uses the energy of the leakage inductance to realize soft switching of the switching tube, reduces the turn-on loss, improves the utilization efficiency of the energy of the leakage inductance, and can also prevent the very high turn-off voltage of the Miller capacitor from being applied to the switching tube at the moment of turn-off of the switching tube. The voltage coupled between the first and second terminals of the switching transistor is prevented from oscillating during the plateau voltage period, thus avoiding the risk of overheating or even damage to the switching transistor. Utilizing soft-switching technology reduces stress on the switching transistor, protecting it and improving the overall stability of the power supply.

[0029] In some embodiments, the switching transistor is a MOSFET, the first connection terminal of the switching transistor is the drain of the MOSFET, and the second connection terminal of the switching transistor is the source of the MOSFET.

[0030] The solution of this invention utilizes the often-wasted leakage inductance voltage to provide power to the resonant network and achieve soft switching of the power supply. By using the energy of the leakage inductance to achieve soft switching of the MOSFET, turn-on losses are reduced, the energy utilization efficiency of the leakage inductance is improved, and the high turn-off peak voltage caused by the Miller capacitance during MOSFET turn-off is also prevented. The voltage coupled between the gate and source of the MOSFET. In terms of voltage, this avoids the risk of overheating or even damage to the MOSFET due to oscillations in the drive voltage during the plateau voltage period. Utilizing soft-switching technology reduces the stress on the MOSFET in the switching power supply, protecting the switching transistor and improving the operating stability of the switching power supply. Specifically, because the MOSFET has Miller capacitance, there is a plateau time during the rise phase of the MOSFET's gate-source voltage. During this time, the voltage value remains constant; this period is called the plateau voltage period.

[0031] Specifically, Figure 2 This is a schematic diagram of a soft-switching circuit according to an embodiment of a novel low-loss power supply topology of the present invention, specifically a modified flyback power supply topology. Figure 2 In the example shown, the power supply energy is rectified and filtered through the AC input to become DC and applied to the power bus. MOSFET M1 is used to switch and adjust the output. A dummy load simulates the electrical equipment. The control IC monitors the bus voltage, current, and output voltage VO, and controls the duty cycle of the switching transistor (such as the MOSFET) to stabilize the output voltage of the switching power supply.

[0032] In some embodiments, the absorption unit comprises: a first diode module, such as diode D1, and a first capacitor module, such as capacitor C1. The non-identical end of the first winding is connected to the anode of the first diode module. The cathode of the first diode module is connected to the second connection end of the first capacitor module. The first connection end of the first capacitor module is connected to the first connection end of the resonance unit. The second connection end of the resonance unit is connected to the second connection end of the first capacitor module. The second connection end of the resonance unit is also connected to the second connection end of the switch tube. Figure 2 In the example shown, diode D1 prevents the transformer T parasitic inductance from resonating with the absorption capacitor.

[0033] In some embodiments, the soft switching device of the switching power supply further comprises: a second diode module, such as diode D2. The second connection end of the first capacitor module is connected to the anode of the second diode module. The cathode of the second diode module is connected to the second connection end of the resonance unit. Figure 2 In the example shown, diode D2 isolates the resonance cavity of the resonance cavity absorption circuit from the absorption circuit to prevent mutual interference.

[0034] In some embodiments, the soft switching device of the switching power supply further comprises: a third diode module, such as diode D3. The first connection end of the first capacitor module is connected to the cathode of the third diode module. The anode of the third diode module is connected to the first connection end of the resonance unit. Figure 2 In the example shown, diode D3 prevents the power bus from charging the resonance cavity of the resonance cavity absorption circuit.

[0035] In some embodiments, the resonance unit comprises: an inductance module, such as inductance L1, and a second capacitor module, such as capacitor C2. The inductance module and the second capacitor module are connected in parallel to form an LC resonance circuit. The first connection end of the LC resonance circuit serves as the first connection end of the resonance unit. The second connection end of the LC resonance circuit serves as the second connection end of the resonance unit and is connected to the second connection end of the switch tube.

[0036] Specifically, as Figure 2As shown, the scheme of the present application proposes a new low-loss power supply topology soft switching circuit, comprising: transformer T, MOS tube M1, inductor L1, capacitor C1, capacitor C2, diode D1, diode D2, diode D3, drive resistor, ground resistor, and controller (such as control IC). The primary winding of the transformer T is two groups, namely the first winding and the second winding, and the power bus of the switching power supply is connected to the same name end of the first winding, and the opposite name end of the first winding is connected to the drain of the MOS tube M1. The source of the MOS tube M1 is grounded through the ground resistor. The same name end of the first winding is connected to the first end of the capacitor C1, the second end of the capacitor C1 is connected to the cathode of the diode D1, and the anode of the diode D1 is connected to the opposite name end of the first winding. The same name end of the first winding is also connected to the cathode of the diode D3, and the anode of the diode D3 is connected to the first end of the parallel inductor L1 and capacitor C2, and the second end of the parallel inductor L1 and capacitor C2 is connected to the source of the MOS tube M1. The first end of the parallel inductor L1 and capacitor C2 is also connected to the drain of the MOS tube M1. The second end of the parallel inductor L1 and capacitor C2 is also connected to the cathode of the diode D2, and the anode of the diode D2 is connected to the cathode of the diode D1. The opposite name end of the secondary winding of the transformer T is connected to the anode of the diode. The cathode of the diode is connected to the same name end of the secondary winding of the transformer T on one hand and to the first end of the dummy load on the other hand. The same name end of the secondary winding of the transformer T is connected to the second end of the dummy load. The controller receives the bus voltage VP detected from the opposite name end of the first winding, receives the switching current detected from the ground resistor connected to the source of the MOS tube M1, and receives the output voltage VO detected from the dummy load, and determines the drive signal for driving the MOS tube M1. The drive signal output by the controller is input to the gate of the MOS tube M1 through the drive resistor.

[0037] In Figure 2 In the example shown, the LC resonance structure composed of the RCD circuit of the switching power supply and the inductor L1 and the capacitor C2 forms a resonance cavity absorption circuit, supplies the originally wasted leakage energy to the LC resonance cavity, and uses the often wasted leakage voltage to provide the resonance network and realize soft switching of the switching power supply, greatly improving the power supply efficiency.

[0038] The technical scheme of the present application is that, by using the RCD circuit based on the switching power supply (such as the flyback isolation switching power supply), the RCD circuit is composed of a resistor module, a capacitor module (such as capacitor C1) and a diode module (such as diode D1), the LC resonant circuit is arranged to replace the resistor module in the RCD circuit, the leakage voltage of the transformer T in the switching power supply is used to supply power to the LC resonant circuit, the resonant circuit is resonated to realize the resonance of the switching tube (such as MOS tube M1) in the switching power supply, so as to reduce the turn-on loss and turn-off loss of the switching tube, thereby, the energy of the leakage inductance in the switching power supply is used to realize the soft switching of the switching tube, and the turn-on loss and turn-off loss of the switching power supply are reduced.

[0039] According to the embodiment of the present application, a switching power supply corresponding to the soft switching device of the switching power supply is also provided. The switching power supply can include the soft switching device of the switching power supply described above.

[0040] Since the processing and functions realized by the switching power supply of the present embodiment are basically corresponding to the embodiments, principles and examples of the device, the description of the present embodiment will not be described in detail, and the related description in the foregoing embodiments can be referred to, which will not be described herein.

[0041] The technical scheme of the present application is that, by using the RCD circuit based on the switching power supply (such as the flyback isolation switching power supply), the RCD circuit is composed of a resistor module, a capacitor module (such as capacitor C1) and a diode module (such as diode D1), the LC resonant circuit is arranged to replace the resistor module in the RCD circuit, the leakage voltage of the transformer T in the switching power supply is used to supply power to the LC resonant circuit, the resonant circuit is resonated to realize the resonance of the switching tube (such as MOS tube M1) in the switching power supply, so as to reduce the turn-on loss and turn-off loss of the switching tube, thereby, the energy of the leakage inductance in the switching power supply is used to realize the soft switching of the switching tube, and the turn-on loss and turn-off loss of the switching power supply are reduced.

[0042] According to the embodiment of the present application, a switching power supply corresponding to the soft switching device of the switching power supply is also provided. The switching power supply can include the soft switching device of the switching power supply described above. Figure 3 As shown in the flowchart of an embodiment of the method of the present application. The control method of the switching power supply can include steps S110 to S140.

[0043] At step S110, the voltage reflected from the secondary winding of the transformer to the primary winding is obtained, denoted as reflected voltage. And the leakage voltage of the transformer is obtained.

[0044] At step S120, according to the reflected voltage and the leakage voltage, the parameters of the components in the absorption unit and the resonant unit are determined, so as to set the components in the absorption unit and the resonant unit according to the parameters of the components in the absorption unit and the resonant unit.

[0045] At step S130, the primary winding of the transformer receives the bus voltage of the power bus to store energy when the switch tube is turned on.

[0046] At step S140, the primary winding of the transformer releases energy to the resonance absorption circuit when the switch tube is turned off. At the moment when the switch tube is turned off, the resonance absorption circuit absorbs the leakage energy generated by the leakage voltage of the transformer and resonates, so that the peak voltage of the switch tube is reduced when the switch tube is turned on in the next cycle, and the soft switching of the switch tube is realized.

[0047] Specifically, Figure 5 The flowchart of an embodiment of the control method of the soft switching circuit of the novel low-loss power supply topology of the application is shown in FIG. 1. As shown in the figure, the control method of the soft switching circuit of the novel low-loss power supply topology proposed by the application comprises the following steps: Figure 5

[0048] Step 11: After the AC power is rectified and filtered, it is output to the power bus.

[0049] Step 12: The primary winding of the transformer T stores energy when the MOS tube M1 is turned on.

[0050] Step 13: The transformer T releases energy to the resonance cavity absorption circuit through the primary winding when the MOS tube M1 is turned off. At the moment when the MOS tube M1 is turned off, the resonance cavity of the resonance cavity absorption circuit absorbs the leakage energy of the transformer T1 and resonates through the resonance circuit. The parameters of the resonance components (such as the inductor L1 and the capacitor C2) in the resonance circuit can be selected by calculation in advance, so that the resonance circuit resonates within a small amplitude range.

[0051] The selection and calculation of the resonance cavity inductor (such as the inductor L1), the resonance capacitor (such as the capacitor C2), and the absorption capacitor (such as the capacitor C1) are as follows: the bus voltage , is the AC input voltage. , V OR is the voltage reflected from the secondary to the primary of the transformer T, Np is the primary turns number, Ns is the secondary turns number, Vo is the output voltage, V F is the diode voltage drop. When the switch tube (such as the MOS tube M1) is turned off, the leakage energy is absorbed by the capacitor C1, and at this time, the voltage across the resistance R1 (i.e. the equivalent resistance of the resonance cavity) and the capacitor C1 network in the absorption circuit is (i.e. the sum of the reflected voltage and the leakage voltage), is the leakage voltage. When the switch tube (such as the MOS tube M1) is turned on, the capacitor C1 discharges through the resistance R1, and before the switch is turned off in the next cycle, ​Reset, so for the control of the discharge time and its strict, here to its discharge time constant R1C1 is 2~4 times the value of R1, R1 is the resistance of the capacitor C1 C1 capacitance value. From the energy point of view (1) is: , wherein, is the original energy of the capacitor C1, is the energy provided by the leakage inductance, is the total energy of the capacitor.

[0052] (1) is expanded then: , wherein L is the leakage inductance voltage, I is the source current, C is the capacitance of the capacitor C1, the leakage inductance energy to the capacitor C1, the capacitor C1 voltage is increased by the increment of the voltage change ΔV, for the voltage capacitor voltage V from the (2) is , the above formula can be obtained , , f is the switching frequency, usually in practical applications due to the influence of other parasitic parameters, will get a larger capacitance, while the resistance is small to meet the requirements of this circuit R1 is the total impedance value of the parallel resonant cavity equivalent past. Inductance impedance , wherein , the capacitance is , C2 is the capacitance of the capacitor C2, so the equivalent impedance , so the selection of the inductance value can be fixed first and then the capacitance value combination.

[0053] Step 14, through the resonant capacitor (such as capacitor C2) clamp MOS tube M1 both ends (ie, the drain of MOS tube M1 and the source of MOS tube M1) voltage in a very small voltage value, in the next cycle when the MOS M1 is turned on again, the peak voltage will be greatly reduced.

[0054] Wherein, the composition of the peak voltage: the peak voltage is generated by the primary leakage inductance of the high frequency transformer, which is superimposed on the switch tube (such as MOS tube M1) after the DC high voltage and the secondary induction voltage, if it exceeds the drain-source voltage will be damaged, so in the design, reference chip manual reduced use switch tube, wherein the switch tube drain-source voltage is composed of the following parts, expressed by the formula: peak voltage , wherein is the bus voltage, is the reflected voltage, is the leakage inductance voltage.

[0055] Referring to Figure 5The example shown, when the switch tube (such as MOS tube M1) is turned on, the power supply loop of the switching power supply is established, and the energy of the power bus can be stored in the primary coil of the transformer T1. When the switch tube (such as MOS tube M1) is turned off, due to the flyback power supply topology, at this time the energy is transmitted backward, and at the same time there is a reverse voltage through the coil (that is, the place where the primary coil of the transformer T1 is connected with the bus) from the secondary winding of the transformer T to the primary winding of the transformer T, and then the leakage inductance voltage of the transformer T is superimposed to make the diode D1 conduct, and the resonant circuit (that is, the resonant cavity absorption circuit) starts to work, and the leakage inductance current of the transformer T flows through the diode D1 to charge the capacitor C1. When the switch tube (such as MOS tube M1) is turned on again, the absorption capacitor (such as capacitor C1) supplies power to the resonant cavity (that is, the resonant circuit composed of capacitor C2 and inductor L1), and the resonant cavity starts to resonate and oscillate within a very small amplitude range. When the switch tube (such as MOS tube M1) is turned off, the drain-source voltage of the MOS tube M1 is clamped to a very small voltage range by the resonant capacitor (such as capacitor C2), at this time it is approximately ZVS (zero voltage switching), so that the MOS tube M1 is turned off, and ZVS turn-off can be realized in the subsequent period, avoiding the high turn-off voltage of the Miller capacitor at the moment of turn-off of the MOS tube M1 coupled to the voltage, thereby avoiding the risk of heating and even damaging the switch tube due to oscillation of the drive voltage during the plateau voltage, and greatly reducing the turn-off loss.

[0056] In some embodiments, the switching power supply control method according to the scheme of the present application further comprises the process of controlling the duty cycle signal of the switch tube.

[0057] The following will be described in detail with reference to the accompanying drawings. Figure 4 The flowchart of an embodiment of the method of the present application for controlling the duty cycle signal of the switch tube is shown in the figure, which further illustrates the specific process of controlling the duty cycle signal of the switch tube, including steps S210 to S230.

[0058] In step S210, the bus voltage of the power bus is obtained, the current between the first connection end of the switch tube and the second connection end of the switch tube is obtained, and the output voltage of the secondary winding is obtained.

[0059] In step S220, the duty cycle signal of the control end of the switch tube is determined according to the bus voltage of the power bus, the current between the first connection end of the switch tube and the second connection end of the switch tube, and the output voltage of the secondary winding.

[0060] In step S230, the turn-on or turn-off of the switch tube is controlled according to the duty cycle signal of the control end of the switch tube.

[0061] Specifically, Figure 6The working flowchart of the PI controller. As shown in Figure 6 The working flowchart of the PI controller includes:

[0062] Step 21, reading the bus voltage VP of the power bus and the current sampling data of the power bus (such as the switching current detected at the ground resistance connected to the source of the MOS tube M1).

[0063] Step 22, the PI regulator adjusts the output voltage VO of the switching power supply by adjusting the duty cycle of the MOS tube M1 according to the bus voltage VP and the current sampling data of the power bus.

[0064] Step 23, according to the feedback of the output voltage VO of the switching power supply, it is judged whether the output voltage VO of the switching power supply is within the calculated adjustment range, and the control is circulated in turn.

[0065] Referring to the example shown in Figure 6 The voltage and current are collected on the power supply main circuit of the switching power supply, it is judged whether the voltage is overvoltage, undervoltage and whether the current is overcurrent through the internal circuit of the control IC chip, it is decided whether the circuit continues to work normally, and at the same time the output voltage V0 is fed back to the control IC through the controllable precision voltage source TL431 and the set voltage value through the photoelectric coupler, the PWM duty cycle of the MOS tube M1 is controlled through the PI regulator, the output voltage of the switching power supply is adjusted constantly, and finally the deviation voltage between the output voltage of the switching power supply and the target voltage is forced to zero, reaching the effect of stable output of the switching power supply (such as flyback isolation switching power supply). According to the experimental data, under the condition that the on-resistance of the MOS tube M1 is constant, the overall loss is significantly reduced, and the heat of the MOS tube M1 is greatly reduced.

[0066] Since the processing and functions realized by the method of the embodiment are basically corresponding to the foregoing embodiments, principles and examples of the switching power supply, the description of the embodiment will not be described in detail, and the related description in the foregoing embodiments will be referred to here.

[0067] By using the technical scheme of the embodiment, the RCD circuit based on the switching power supply (such as flyback isolation switching power supply) is used, the RCD circuit is composed of a resistance module, a capacitor module (such as capacitor C1) and a diode module (such as diode D1), the LC resonant circuit is used to replace the resistance module in the RCD circuit, the leakage inductance voltage of the transformer T in the switching power supply is used to power the LC resonant circuit, the resonant circuit resonates to realize the resonance of the switching tube (such as MOS tube M1) in the switching power supply to reduce the turn-on loss and turn-off loss of the switching tube, the soft switching of the MOSFET is realized by using the energy of the leakage inductance, the turn-on loss is reduced, and the utilization efficiency of the energy of the leakage inductance is improved.

[0068] In summary, the person skilled in the art can easily understand that the above-mentioned advantageous modes can be freely combined and superimposed without conflict.

[0069] The above merely provides an example of the present application, and is not intended to limit the present application. The present application can be variously changed and modified by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall fall within the scope of claims of the present application.

Claims

1. A soft-switching device for a switching power supply, characterized in that, The switching power supply includes: a transformer and a switching transistor; the transformer has a primary winding and a secondary winding; the primary winding includes a first winding; the power bus of the switching power supply is connected to the same-name terminal of the first winding; the opposite-name terminal of the first winding is connected to the first connection terminal of the switching transistor; the second connection terminal of the switching transistor is grounded; the secondary winding outputs to the load; the soft-switching device of the switching power supply includes: an absorption unit and a resonant unit. The absorption unit includes: a first diode module and a first capacitor module; wherein, the opposite terminal of the first winding is connected to the anode of the first diode module; the cathode of the first diode module is connected to the second connection terminal of the first capacitor module; the first connection terminal of the first capacitor module is connected to the first connection terminal of the resonant unit; the second connection terminal of the resonant unit is connected to the second connection terminal of the first capacitor module; the second connection terminal of the resonant unit is also connected to the second connection terminal of the switching transistor; the first connection terminal of the resonant unit is connected to the first connection terminal of the switching transistor. The resonant unit includes: an inductor module and a second capacitor module; wherein the inductor module and the second capacitor module are connected in parallel to form an LC resonant circuit; the first connection terminal of the LC resonant circuit serves as the first connection terminal of the resonant unit; the second connection terminal of the LC resonant circuit serves as the second connection terminal of the resonant unit and is connected to the second connection terminal of the switching transistor. The first connection terminal of the switching transistor is connected to the second connection terminal of the switching transistor via the first diode module in the absorption unit, the second diode module between the absorption unit and the resonant unit, and the resonant unit, forming a resonant absorption circuit. This circuit absorbs the leakage inductance energy of the transformer and resonates at the instant the switching transistor is turned off when it is turned off, thereby reducing the peak voltage of the switching transistor when it is turned on in the next cycle and realizing soft switching of the switching transistor.

2. The soft-switching device for a switching power supply according to claim 1, characterized in that, The switching transistor is a MOSFET, the first connection terminal of the switching transistor is the drain of the MOSFET, and the second connection terminal of the switching transistor is the source of the MOSFET.

3. The soft-switching device for a switching power supply according to claim 1, characterized in that, The soft-switching device of the switching power supply further includes: a second diode module; wherein, The second connection terminal of the first capacitor module is connected to the anode of the second diode module; the cathode of the second diode module is connected to the second connection terminal of the resonant unit.

4. The soft-switching device for a switching power supply according to claim 1, characterized in that, The soft-switching device of the switching power supply further includes: a third diode module; wherein, The first connection terminal of the first capacitor module is connected to the cathode of the third diode module; the anode of the third diode module is connected to the first connection terminal of the resonant unit.

5. A switching power supply, characterized in that, include: The soft-switching device of the switching power supply as described in any one of claims 1 to 4.

6. A control method for a switching power supply as described in claim 5, characterized in that, include: Obtain the voltage reflected from the secondary winding to the primary winding of the transformer, denoted as the reflected voltage; and obtain the leakage inductance voltage of the transformer. Based on the reflected voltage and the leakage inductance voltage, the parameters of the components in the absorption unit and the resonant unit are determined, so as to set the components in the absorption unit and the resonant unit according to the parameters of the components in the absorption unit and the resonant unit. When the switching transistor is turned on, the primary winding of the transformer receives the bus voltage of the power supply bus and stores energy. When the switching transistor is turned off, the primary winding of the transformer releases energy to the resonant absorption circuit; At the instant the switch is turned off, the resonant absorption circuit absorbs the leakage inductance energy generated by the leakage inductance voltage of the transformer and resonates, so that the peak voltage of the switch is reduced when the switch is turned on in the next cycle, thereby realizing the soft switching of the switch.

7. The control method for a switching power supply according to claim 6, characterized in that, Also includes: Obtain the bus voltage of the power supply bus, obtain the current between the first connection terminal and the second connection terminal of the switching transistor, and obtain the output voltage of the secondary winding; The duty cycle signal of the control terminal of the switch is determined based on the bus voltage of the power bus, the current between the first connection terminal and the second connection terminal of the switch, and the output voltage of the secondary winding. The switching transistor is turned on or off according to the duty cycle signal at the control terminal of the switching transistor.

Images