Switching power supply circuit, control method thereof, chip and electronic equipment

Abstract

The invention relates to the technical field of switching power supplies, in particular to a switching power supply circuit, a control method thereof, a chip and electronic equipment. The switching power supply circuit comprises a transformer, a primary control circuit, a secondary control circuit, a first transistor, a second transistor, a third transistor and at least one discharge branch, the third transistor is arranged in a secondary winding loop of the transformer, and a control electrode of the third transistor is connected with the secondary control circuit. According to the switching power supply circuit provided by the invention, after the secondary control circuit controls to open the second transistor, the current on the transformer is gradually reduced and reversed, then the secondary control circuit controls to open the third transistor, and the discharge branch is turned off at the same time, at the moment, the negative current value in the transformer lasts for a period of time until the second transistor is turned off; when the negative current value in the transformer is gradually reduced, the first transistor is controlled to be turned on, so that zero-voltage switching of the first transistor can be realized, and the working efficiency of the switching power supply circuit is improved.

Description

Technical Field

[0001] The present application relates to the technical field of switching power supplies, and in particular to a switching power supply circuit and a control method thereof, a chip, and an electronic device. Background Art

[0002] With the development of electronic technology, the charging efficiency and charging safety of electronic devices are an issue that people are concerned about. In the related art, the switching power supply circuit for fast charging of electronic devices usually includes a transformer, a primary switch tube, a secondary switch tube, a primary control unit and a secondary control unit. Among them, the primary switch tube is arranged in the primary winding loop of the transformer, and the secondary switch tube is arranged in the secondary winding loop of the transformer. The transformer is used to convert the input power supply voltage, and then make the secondary winding output a charging voltage that is adapted to the electronic device. The primary control unit and the secondary control unit are respectively used to control the conduction or shutdown of the primary switch tube and the secondary switch tube, so as to control the switching power supply circuit to work in different charging modes to meet the charging needs of various scenarios.

[0003] In the related art, the primary control unit controls the on or off of the primary switch tube, thereby controlling the on or off of the switching power supply circuit. However, each time the primary control unit controls the primary switch tube to be on, the primary switch tube does not achieve zero voltage switching (Zero Voltage Switch, referred to as ZVS). Therefore, the switch tube loss of the switching power supply circuit is large, affecting the working efficiency of the switching power supply circuit. Summary of the invention

[0004] The present application provides a switching power supply circuit and a control method thereof, a chip, and an electronic device to solve the technical problem in the related art that the switching tube cannot achieve zero voltage switching, resulting in large switching tube losses in the switching power supply circuit.

[0005] In a first aspect, the present application provides a switching power supply circuit, including: a transformer, a primary control circuit, a secondary control circuit, a first transistor, a second transistor, a third transistor, and at least one discharge branch;

[0006] The same-name end of the primary winding of the transformer is used to receive the power supply voltage, the opposite-name end of the primary winding is connected to the first electrode of the first transistor, and the second electrode of the first transistor is grounded; the control electrode of the first transistor is connected to the primary control circuit, and the primary control circuit is used to control the conduction and shutdown of the first transistor;

[0007] The opposite-name end of the secondary winding of the transformer is connected to the first electrode of the third transistor, the second electrode of the third transistor is connected to the second electrode of the second transistor, the first electrode of the second transistor is connected to the same-name end of the secondary winding, and the control electrodes of the second transistor and the third transistor are connected to the secondary control circuit, and the secondary control circuit is used to control the conduction and disconnection of the second transistor and the third transistor;

[0008] The opposite-polarity end of the secondary winding of the transformer is connected to the input end of the at least one discharge branch, and the output end of the at least one discharge branch is used to output a discharge voltage; at least one switch circuit is provided on each discharge branch, and the control end of the switch circuit is also connected to the secondary control circuit;

[0009] The secondary control circuit is used to control the on or off of the switch circuit on the discharge branch, thereby controlling the discharge branch to output a corresponding discharge voltage.

[0010] In a possible design, it further includes a first diode and a first capacitor; the positive electrode of the first diode is connected to the opposite end of the secondary winding, the negative electrode of the first diode is connected to the first end of the first capacitor, and the second end of the first capacitor is grounded;

[0011] Wherein, the first end of the first capacitor is also connected to the power supply end of the secondary control circuit.

[0012] In a possible design, a second capacitor is also included, wherein the first end of the second capacitor is connected to the opposite end of the secondary winding, and the second end of the second capacitor is connected to the bootstrap capacitor pin of the secondary control circuit; the first end of the second capacitor is also connected to the level switching pin of the secondary control circuit.

[0013] In a possible design, each of the discharge branches includes an energy storage capacitor, a first end of the energy storage capacitor is connected to the discharge branch, and a second end of the energy storage capacitor is grounded.

[0014] In a possible design, an isolation circuit is further included, and the primary control circuit is connected to the secondary control circuit through the isolation circuit.

[0015] In a possible design, the switch circuit includes a first MOS transistor, a second MOS transistor, a second diode, a third capacitor and a first resistor;

[0016] The first MOS transistor and the second MOS transistor are a group of back-to-back MOS transistors, the first electrode of the first MOS transistor is connected to the opposite end of the secondary winding, the second electrode of the first MOS transistor is connected to the second electrode of the second MOS transistor, and the first electrode of the second MOS transistor is the output end of the discharge branch; the control electrode of the first MOS transistor is connected to the secondary control circuit; the control electrode of the second MOS transistor is connected to the first end of the third capacitor, and the second end of the third capacitor is connected to the secondary control circuit;

[0017] The anode of the second diode is connected to the first electrode of the second MOS tube, and the cathode of the second diode is connected to the control electrode of the second MOS tube; the first resistor is connected in parallel to both ends of the second diode.

[0018] In a possible design, two discharge branches are included, and the two discharge branches are respectively a first discharge branch and a second discharge branch;

[0019] The first discharge branch is provided with a first switch circuit, the first switch circuit comprises a third MOS transistor, a first pole of the third MOS transistor is connected to the opposite end of the secondary winding, and a second pole of the third MOS transistor is the output end of the first discharge branch;

[0020] The second discharge branch is provided with a second switch circuit, and the second switch circuit includes a fourth MOS transistor, a fifth MOS transistor, a third diode, a fourth capacitor and a second resistor;

[0021] The fourth MOS tube and the fifth MOS tube are a group of back-to-back MOS tubes, the first electrode of the fourth MOS tube is connected to the opposite end of the secondary winding, the second electrode of the fourth MOS tube is connected to the second electrode of the fifth MOS tube, and the first electrode of the fifth MOS tube is the output end of the second discharge branch; the control electrode of the fourth MOS tube is connected to the secondary control circuit; the control electrode of the fifth MOS tube is connected to the first end of the fourth capacitor, and the second end of the fourth capacitor is connected to the secondary control circuit; the positive electrode of the third diode is connected to the first electrode of the fifth MOS tube, and the negative electrode of the third diode is connected to the control electrode of the fifth MOS tube; the second resistor is connected in parallel to both ends of the third diode.

[0022] In a possible design, when the switching power supply circuit operates in the first discontinuous conduction mode, within one working cycle:

[0023] The primary control circuit is used to control the first transistor to turn on so that the current value on the transformer increases, and to turn off the first transistor after the turn-on time of the first transistor reaches a first preset time length;

[0024] The secondary control circuit is used for controlling the second transistor to be turned on at the moment when the first transistor is turned off;

[0025] The secondary control circuit is further used for controlling the discharge branch to be turned off and the third transistor to be turned on after the turn-on time of the second transistor reaches a second preset time; and controlling the third transistor to be turned off and the discharge branch to be turned on and the second transistor to be turned off after the turn-on time of the third transistor reaches a third preset time.

[0026] The primary control circuit is further configured to control turning on the first transistor after a fourth preset time period has passed after the second transistor is turned off.

[0027] In a possible design, when the switching power supply circuit operates in the second discontinuous conduction mode, within one working cycle:

[0028] The primary control circuit is used to control the first transistor to turn on so that the current value on the transformer increases, and to turn off the first transistor after the turn-on time of the first transistor reaches a first preset time length;

[0029] The secondary control circuit is used for controlling the second transistor to be turned on, and the third transistor to be turned off, and the discharge branch to be turned on at the moment when the first transistor is turned off;

[0030] The secondary control circuit is further used for controlling the third transistor to be turned on and the discharge branch to be turned off after the turn-off time of the third transistor reaches a fifth preset time length;

[0031] The secondary control circuit is further configured to control turning off the second transistor after the on time of the second transistor reaches a sixth preset time length;

[0032] The primary control circuit is further configured to control turning on the first transistor after a seventh preset time period has passed after the second transistor is turned off.

[0033] In a possible design, when the switching power supply circuit operates in a continuous conduction mode, within one working cycle:

[0034] The primary control circuit is used to control the first transistor to turn on;

[0035] The secondary control circuit is used to control the third transistor to turn on, the second transistor to turn off, and the discharge branch to disconnect when the first transistor is turned on;

[0036] The primary control circuit is further configured to control the first transistor to be turned off after the on time of the first transistor reaches an eighth preset time;

[0037] The secondary control circuit is further used for controlling the third transistor to be turned off, the second transistor to be turned on, and the discharge branch to be turned on when the first transistor is turned off.

[0038] In a second aspect, the present application further provides a control method for a switching power supply circuit, the switching power supply circuit comprising: a transformer, a primary control circuit, a secondary control circuit, a first transistor, a second transistor, a third transistor and at least one discharge branch; the same-name end of the primary winding of the transformer is used to receive a power supply voltage, the opposite-name end of the primary winding is connected to the first electrode of the first transistor, and the second electrode of the first transistor is grounded; the control electrode of the first transistor is connected to the primary control circuit; the opposite-name end of the secondary winding of the transformer is connected to the first electrode of the third transistor, the second electrode of the third transistor is connected to the second electrode of the second transistor, the first electrode of the second transistor is connected to the same-name end of the secondary winding, and the control electrodes of the second transistor and the third transistor are connected to the secondary control circuit; the first electrode of the third transistor is connected to the input end of the at least one discharge branch, and the output end of the at least one discharge branch is used to output a discharge voltage; at least one switch circuit is provided on each of the discharge branches, and the control end of the switch circuit is also connected to the secondary control circuit;

[0039] When the switching power supply circuit operates in a first discontinuous conduction mode, within a working cycle, the control method includes:

[0040] Controlling the first transistor to turn on so that the current value on the transformer increases, and turning off the first transistor after the turn-on time of the first transistor reaches a first preset time length;

[0041] At the moment of closing the first transistor, controlling to open the second transistor;

[0042] After the on-time of the second transistor reaches a second preset time length, the discharge branch is controlled to be turned off, and the third transistor is controlled to be turned on at the same time; and after the on-time of the third transistor reaches a third preset time length, the third transistor is controlled to be turned off, and the switch circuit is controlled to turn on the discharge branch, and the second transistor is controlled to be turned off;

[0043] After the second transistor is turned off, after a fourth preset time period, the first transistor is controlled to be turned on.

[0044] In a possible design, when the switching power supply circuit operates in the second discontinuous conduction mode, within a working cycle, the control method further includes:

[0045] Controlling the first transistor to turn on so that the current value on the transformer increases, and turning off the first transistor after the turn-on time of the first transistor reaches a first preset time length;

[0046] At the moment of closing the first transistor, controlling to open the second transistor, and controlling to close the third transistor, and controlling to turn on the discharge branch;

[0047] After the closing time of the third transistor reaches a fifth preset time length, controlling to turn on the third transistor, and at the same time controlling the switch circuit to turn off the discharge branch;

[0048] After the on time of the second transistor reaches a sixth preset time length, controlling to turn off the second transistor;

[0049] After the second transistor is turned off, after a seventh preset time period, the first transistor is controlled to be turned on.

[0050] In a possible design, when the switching power supply circuit operates in a continuous conduction mode, within a working cycle, the control includes:

[0051] Controlling the first transistor to turn on;

[0052] At the moment when the first transistor is turned on, controlling the third transistor to be turned on, controlling the second transistor to be turned off, and controlling the switch circuit to disconnect the discharge branch;

[0053] After the turn-on time of the first transistor reaches an eighth preset time, controlling the first transistor to turn off;

[0054] At the moment when the first transistor is turned off, the third transistor is controlled to be turned off, the second transistor is controlled to be turned on, and the switch circuit is controlled to turn on the discharge branch.

[0055] In a third aspect, the present application also provides a chip, which includes a switching power supply circuit as described in any one of the above items.

[0056] In a fourth aspect, the present application also provides an electronic device, which includes a switching power supply circuit as described in any one of the above items; or includes a chip as described above.

[0057] The switching power supply circuit provided by the first aspect above includes: a transformer, a primary control circuit, a secondary control circuit, a first transistor, a second transistor, a third transistor and at least one discharge branch; wherein the same-name end of the primary winding of the transformer is used to receive the power supply voltage, the opposite-name end of the primary winding is connected to the first electrode of the first transistor, and the second electrode of the first transistor is grounded; the control electrode of the first transistor is connected to the primary control circuit, and the primary control circuit is used to control the conduction and shutdown of the first transistor; the opposite-name end of the secondary winding of the transformer is connected to the first electrode of the third transistor, and the second electrode of the third transistor is connected to the second transistor The second pole of the second transistor is connected to the same-name end of the secondary winding, the control poles of the second transistor and the third transistor are connected to the secondary control circuit, and the secondary control circuit is used to control the conduction and shutoff of the second transistor and the third transistor; the first pole of the third transistor is connected to the input end of at least one discharge branch, and the output end of at least one discharge branch is used to output the discharge voltage; at least one switch circuit is provided on each discharge branch, and the control end of the switch circuit is also connected to the secondary control circuit; the secondary control circuit is used to control the conduction or shutoff of the switch circuit on the discharge branch, so as to control the discharge branch to output the corresponding discharge voltage. According to the switching power supply circuit provided by the present application, after the secondary control circuit controls to turn on the second transistor, the current on the transformer gradually decreases and reverses, and then the secondary control circuit controls to turn on the third transistor and turn off the discharge branch at the same time. At this time, the negative current value in the transformer will continue for a period of time until the second transistor is turned off, and the negative current value in the transformer will gradually decrease. At this time, the first transistor is controlled to be turned on, and the zero voltage switch of the first transistor can be realized, thereby improving the working efficiency of the switching power supply circuit.

[0058] The beneficial effects provided in the above-mentioned second aspect and various possible designs of the above-mentioned second aspect can refer to the beneficial effects brought about by the above-mentioned first aspect and various possible implementation methods of the first aspect, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technologies, the drawings required for use in the embodiments or the related technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0060] Figure 1 A schematic diagram of the switching power supply circuit structure provided for the related technology;

[0061] Figure 2 One of the structural schematic diagrams of the switching power supply circuit provided in the embodiment of the present application;

[0062] Figure 3The second structural schematic diagram of the switching power supply circuit provided in the embodiment of the present application;

[0063] Figure 4 The third structural diagram of the switching power supply circuit provided in the embodiment of the present application;

[0064] Figure 5 A fourth structural schematic diagram of a switching power supply circuit provided in an embodiment of the present application;

[0065] Figure 6 A fifth structural diagram of a switching power supply circuit provided in an embodiment of the present application;

[0066] Figure 7 The sixth structural diagram of the switching power supply circuit provided in the embodiment of the present application;

[0067] Figure 8 A waveform diagram of a switching power supply circuit provided in an embodiment of the present application in a working mode;

[0068] Fig. 9 A flowchart of a switching power supply circuit in a working mode provided in an embodiment of the present application;

[0069] Fig.10 A waveform diagram of the switching power supply circuit provided in an embodiment of the present application in another working mode;

[0070] Fig.11 A working flow chart of the switching power supply circuit provided in an embodiment of the present application in another working mode;

[0071] Fig.12 A waveform diagram of the switching power supply circuit provided in an embodiment of the present application in another working mode;

[0072] Fig.13 A working flow chart of the switching power supply circuit provided in an embodiment of the present application in another working mode;

[0073] Fig.14 One of the control method flow charts provided in the embodiment of the present application;

[0074] Fig.15 The second flow chart of the control method provided in the embodiment of the present application;

[0075] Fig.16 The third flow chart of the control method provided in the embodiment of the present application. DETAILED DESCRIPTION

[0076] In this application, "at least one" means one or more, and "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c alone can represent: a, b, c, a and b, a and c, or a, b, and c, where a, b, and c can be single or multiple. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0077] The directions or positional relationships indicated by terms such as "center", "longitudinal", "lateral", "up", "down", "left", "right", "front", and "back" are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present application and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present application.

[0078] The terms "connected" and "connected" should be understood in a broad sense. For example, the "connected" or "connected" of a circuit structure can refer to not only physical connection, but also electrical connection or signal connection. For example, it can be directly connected, that is, physically connected, or indirectly connected through at least one intermediate element, as long as the circuit is connected, or it can be the internal connection of two elements; signal connection can refer to signal connection through a circuit or through a media medium, such as radio waves. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0079] The transistor in the present application is a three-terminal transistor, and its three terminals are a control electrode, a first electrode, and a second electrode. The transistor can be a bipolar transistor or a field effect transistor, etc. For example, when the transistor is a bipolar transistor, its control electrode refers to the base of the bipolar transistor, the first electrode can be the collector or emitter of the bipolar transistor, and the corresponding second electrode can be the emitter or collector of the bipolar transistor; when the transistor is a field effect transistor, its control electrode refers to the gate of the field effect transistor, the first electrode can be the drain or source of the field effect transistor, and the corresponding second electrode can be the source or drain of the field effect transistor.

[0080] With the development of fast charging technology, switching power supply circuits with high power and multi-channel output have become a trend in market demand. For example, a fast charging adapter can achieve two outputs at the same time. One output can power an electronic device with a USB Type-C interface, and the other output can charge an electronic device with a USB Type-A interface. The two outputs can charge two electronic devices at the same time without affecting each other.

[0081] In order to achieve the above technical purpose, a switching power supply circuit is provided in the related art. Figure 1 For the schematic diagram of the switching power supply circuit structure provided for related technologies, please refer to Figure 1 As shown, the switching power supply circuit includes a first transformer T1, a primary switch tube Q10, a secondary switch tube Q20, a primary control unit 10, an isolation unit 11 and a secondary control unit 12. The primary switch tube Q10 is arranged in the primary winding loop of the first transformer T1. Specifically, the first pole of the primary switch tube Q10 is connected to the opposite end of the primary winding, the second pole of the primary switch tube Q10 is grounded GND, the control pole of the primary switch tube Q10 is connected to the primary control unit 10, and the primary control unit 10 is used to control the conduction or shutdown of the primary switch tube Q10. The secondary switch tube Q20 is arranged in the secondary winding loop of the first transformer T1. Specifically, the first pole of the secondary switch tube Q20 is connected to the same end of the secondary winding of the first transformer T1, the second pole of the secondary switch tube Q20 is grounded, and the control pole SDRV1 of the secondary switch tube Q20 is connected to the secondary control unit 12. The first transformer T1 is used to convert the input power supply voltage, and then make the secondary winding output a charging voltage adapted to the electronic device. The primary control unit 10 and the secondary control unit 12 are used to control the on or off of the primary switch tube Q10 and the secondary switch tube Q20 respectively, so as to control the switching power supply circuit to operate in different charging modes to meet the charging requirements of various scenarios.

[0082] Please continue to see Figure 1The switching power supply circuit provided by the related technology includes two charging output terminals, namely the first charging output terminal Vo1 and the second charging output terminal Vo2. The opposite-name end of the secondary winding loop of the first transformer T1 is a high-voltage end, and the opposite-name end of the secondary winding loop is connected to the first charging output terminal Vo1 and the second charging output terminal Vo2 respectively. In addition, the first charging output terminal Vo1 is grounded to GND through the first energy storage capacitor C10, and the second charging output terminal Vo2 is grounded to GND through the second energy storage capacitor C10. In addition, a first switch S10 is also connected in series between the opposite-name end of the secondary winding loop and the first charging output terminal Vo1, and a second switch S20 is also connected in series between the opposite-name end of the secondary winding loop and the second charging output terminal Vo2. The control ends of the first switch S10 and the second switch S10 are both connected to the secondary control unit 12. During operation, the secondary control unit 12 controls the first switch S10 and the second switch S20 to turn on or off according to the duty cycle signal, thereby controlling the energy proportion of the first charging output terminal Vo1 and the second charging output terminal Vo2, thereby adjusting the two charging outputs without affecting each other.

[0083] according to Figure 1 In the switching power supply circuit shown in the related art, during operation, each time the primary control unit 10 controls the primary switch tube Q10 to turn on, the primary switch tube Q10 is not a zero voltage switch (ZVS for short). Therefore, the switch tube loss is greatly increased, affecting the working efficiency of the switching power supply circuit. In addition, during operation of the switching power supply circuit, the voltage signal SRV1 on the opposite-name end of the secondary winding and the voltage signal SRD1 on the same-name end both have large voltage spikes, which will also affect the working efficiency and stability of the circuit.

[0084] In order to overcome the defects in the above-mentioned related technologies, the present application provides a switching power supply circuit. On the basis of the related technologies, the switching power supply circuit adds a third transistor in the secondary winding loop, the first electrode of the third transistor is connected to the opposite end of the secondary winding, the second electrode of the third transistor is connected to the same end of the secondary winding, the control electrode of the third transistor is connected to the secondary control unit, and the secondary control unit outputs a driving signal to control the conduction or shutdown of the third transistor. According to the switching power supply circuit provided by the present application, after the secondary control circuit controls to turn on the secondary transistor, the current on the transformer gradually decreases and reverses, and then the secondary control circuit controls to turn on the third transistor and turns off the discharge branch at the same time. At this time, the negative current value in the transformer will continue for a period of time until the secondary transistor is turned off. The negative current value in the transformer will gradually decrease. At this time, the primary transistor is controlled to be turned on, which can realize the zero voltage switch of the primary transistor and improve the working efficiency of the switching power supply circuit.

[0085] The switching power supply circuit provided in the present application is further described below in conjunction with the accompanying drawings and specific implementations.

[0086] Figure 2 One of the structural schematic diagrams of the switching power supply circuit provided in the embodiment of the present application is shown in FIG. Figure 2 As shown, the switching power supply circuit provided in this embodiment includes: a second transformer T2, a primary control circuit 21, a secondary control circuit 22, a first transistor Q20, a second transistor Q21, a third transistor Q22 and at least one discharge branch.

[0087] Among them, the same-name end of the primary winding of the transformer is used to receive the power supply voltage VIN, the opposite-name end D of the primary winding is connected to the first end of the first transistor Q20, and the second electrode of the first transistor Q20 is grounded; the control electrode PDRV of the first transistor Q20 is connected to the primary control circuit 21, and the primary control circuit 21 is used to output a corresponding drive control signal to control the conduction and shutdown of the first transistor Q20.

[0088] The opposite-name terminal SRV of the secondary winding of the transformer is connected to the first electrode of the third transistor Q22, the second electrode of the third transistor Q22 is connected to the second electrode of the second transistor Q21, the first electrode of the second transistor Q21 is connected to the same-name terminal SRD of the secondary winding, and the control electrodes of the second transistor Q21 and the third transistor Q22 are both connected to the secondary control circuit 22, and the secondary control circuit 22 is used to output corresponding drive control signals to control the conduction and shutoff of the second transistor Q21 and the third transistor Q22. Specifically, the secondary control circuit 22 is provided with a plurality of drive signal terminals, for example, the secondary control circuit 22 is provided with two drive signal terminals, wherein one drive signal terminal is connected to the control electrode SDRV of the second transistor Q21, and the other drive signal terminal is connected to the control electrode S0 of the third transistor Q22.

[0089] Among them, the opposite-name end of the secondary winding of the second transformer T2 is connected to the input end of at least one discharge branch, that is, the first electrode of the third transistor Q22 is connected to the input end of at least one discharge branch, and the output end of at least one discharge branch is used to output a discharge voltage; at least one switch circuit is arranged on each discharge branch, and the control end of the switch circuit is also connected to the secondary control circuit 22; the secondary control circuit 22 is used to control the conduction or disconnection of the switch circuit on the discharge branch, so as to control the discharge branch to output the corresponding discharge voltage.

[0090] It can be seen that, compared with the switching power supply circuit provided by the related art, the switching power supply circuit provided by this embodiment adds a third transistor Q22, the first electrode of the third transistor Q22 is connected to the opposite end of the secondary winding of the transformer, and the second electrode of the third transistor Q22 is connected to the second electrode of the second transistor Q21. According to the switching power supply circuit provided by the present application, after the secondary control circuit 22 controls to turn on the secondary transistor, the current Lm on the second transformer T2 gradually decreases and reverses, and then the secondary control circuit 22 controls to turn on the third transistor Q22, and at the same time turns off all discharge branches. At this time, the negative current value in the second transformer T2 will continue for a period of time until the second transistor Q21 is turned off, and the negative current value in the transformer will gradually decrease. At this time, the first transistor Q20 is controlled to be turned on, and the zero voltage switch of the first transistor Q20 can be realized, thereby improving the working efficiency of the switching power supply circuit.

[0091] In this embodiment, the first transistor Q20, the second transistor Q21 and the third transistor Q22 can be NMOS (N-Metal-Oxide-Semiconductor) tubes. In other embodiments, the first transistor Q20, the second transistor Q21 and the third transistor Q22 can also be PMOS (P-Metal-Oxide-Semiconductor) tubes. For example, when the first transistor Q20, the second transistor Q21 and the third transistor Q22 are NMOS tubes, the first pole is the drain, the second pole is the source, and the control pole is the gate.

[0092] In one embodiment, see Figure 2 As shown, the switching power supply circuit also includes an isolation circuit 23, and the primary control circuit 21 is electrically connected to the secondary control circuit 22 through the isolation circuit. It can be understood that in the isolated switching power supply circuit, the isolation circuit 23 mainly plays the role of safety, stability and noise isolation to ensure the stable operation of the switching power supply, and the isolation circuit 23 will not be described in detail here.

[0093] Please continue to see Figure 2 As shown, in one embodiment, the switching power supply circuit further includes a first diode D1 and a first capacitor C21. The anode of the first diode D1 is connected to the opposite end of the secondary winding, the cathode of the first diode D1 is connected to the first end of the first capacitor C21, and the second end of the first capacitor C21 is grounded GND; the first end of the first capacitor C21 is also connected to the power supply end VDD of the secondary control circuit 22.

[0094] According to the switching power supply circuit provided in this embodiment, during operation, the energy of the voltage glitch on SRV will be transmitted to the first capacitor C21 through the first diode D1 for storage at the opposite-name end SRV of the secondary winding, so that the energy stored in the first capacitor C21 can be used to power the secondary control circuit 22. This not only eliminates the voltage glitch in the secondary circuit and ensures the stability of the output discharge voltage of the switching power supply circuit, but also can power the secondary control circuit 22 with the energy of the voltage glitch, thereby improving the energy conversion efficiency of the switching power supply circuit.

[0095] In other embodiments, there are various ways to power the secondary control circuit 22. For example, the secondary control circuit 22 may be powered from the opposite-signal terminal SRV, or from the first discharge branch Vo3 and the second discharge branch Vo4.

[0096] Please continue to see Figure 2 As shown, in one embodiment, the switching power supply circuit further includes a second capacitor C22, the first end of the second capacitor C22 is connected to the opposite end SRV of the secondary winding, the second end of the second capacitor C22 is connected to the bootstrap capacitor pin of the secondary control circuit 22, and the bootstrap capacitor pin can be referred to as the BST (Boost-trap) pin; the first end of the second capacitor C22 is also connected to the level switching pin of the secondary control circuit 22. BST and the level switching pin are two important pins in the power chip, and they are particularly common in the BUCK power chip. The bootstrap capacitor pin is usually connected to the level switching pin through a 100nF capacitor, and the level switching pin is referred to as the SW (Switch Pin) pin. The second capacitor C22 between the bootstrap capacitor pin and the level switching pin is also called a bootstrap capacitor, which plays a key role. When the low-side N-tube is turned off, since the voltage across the second capacitor C22 cannot change suddenly, the bootstrap capacitor pin voltage will be 5V higher than the level switching pin voltage. This bootstrap capacitor directly provides voltage to the high-side drive circuit, so that the high-end N-tube can be turned on. This mechanism ensures the normal operation of the power chip.

[0097] In one embodiment, Figure 3 For the second structural diagram of the switching power supply circuit provided in the embodiment of the present application, please refer to Figure 3 As shown, when there is no need to power the second capacitor C22 and the power supply terminal VDD of the secondary control circuit 22 through the opposite-name terminal SRV, the first end of the second capacitor C22 is also connected to the power supply terminal VDD of the secondary control circuit 22 to power the secondary control circuit 22 through the voltage at the SRV point.

[0098] In one embodiment, Figure 4 The third structural diagram of the switching power supply circuit provided in the embodiment of the present application is shown in FIG. Figure 4As shown, when there is no need to power the bootstrap capacitor, that is, when there is no need to power the second capacitor C22 through the alternative terminal SRV, the bootstrap capacitor between the bootstrap capacitor pin and the level switching pin can be powered by an external power supply inside the secondary control circuit 22.

[0099] In addition, in general, the capacitance value of the second capacitor C22 can be 100nF, and the bootstrap capacitor pin is connected to the level switching pin through a 100nF capacitor. This connection method can effectively reduce the switching noise of the power chip and improve the efficiency and stability of the power chip.

[0100] Generally, in the switching power supply circuit of this embodiment, each discharge branch includes an energy storage capacitor, and the first end of the energy storage capacitor is connected to the discharge branch, that is, the energy storage capacitor is used to be connected to the input end of the discharge branch, and the second end of the energy storage capacitor is grounded GND. During operation, when a certain discharge branch is turned on, the opposite-name end SRV of the secondary winding will charge the energy storage capacitor on the discharge branch while outputting a discharge voltage to the discharge branch, so that the energy storage capacitor stores energy, and when the input end of the discharge branch is disconnected from the opposite-name end SRV of the secondary winding, the energy storage capacitor can continue to supply power to the outside.

[0101] Among them, the switch circuit on the discharge branch in this embodiment is usually implemented by two back-to-back MOS tubes. The MOS tube can be a power device such as a MOSFET tube, a GaN tube, and a SiC tube, which is not limited here.

[0102] In one embodiment, the switch circuit includes a first MOS tube, a second MOS tube, a second diode, a third capacitor and a first resistor; the first MOS tube and the second MOS tube are a group of back-to-back MOS tubes, the first electrode of the first MOS tube is connected to the opposite end of the secondary winding, the second electrode of the first MOS tube is connected to the second electrode of the second MOS tube, and the first electrode of the second MOS tube is the output end of the discharge branch; the control electrode of the first MOS tube is connected to the secondary control circuit; the control electrode of the second MOS tube is connected to the first end of the third capacitor, and the second end of the third capacitor is connected to the secondary control circuit; the positive electrode of the second diode is connected to the first electrode of the second MOS tube, and the negative electrode of the second diode is connected to the control electrode of the second MOS tube; the first resistor is connected in parallel at both ends of the second diode. The first electrode of the second MOS tube is connected to the output end of the discharge branch, and the voltage of the output end of the discharge branch does not change drastically, so that the third capacitor can drive the first MOS tube and the second MOS tube in a bootstrap manner.

[0103] In one embodiment, if Figure 2As shown, the switch power supply circuit includes two discharge branches, which are respectively a first discharge branch Vo3 and a second discharge branch Vo4. Among them, a first energy storage capacitor C23 is provided in the first discharge branch Vo3, and the first end of the first energy storage capacitor C23 is connected to the first discharge branch Vo3, and the second end of the first energy storage capacitor C23 is grounded GND, that is, the second end of the first energy storage capacitor C23 is also the grounding end of the first discharge branch, and together with the first discharge branch Vo3, an output loop is formed. A second energy storage capacitor C24 is provided in the second discharge branch Vo4, and the first end of the second energy storage capacitor C24 is connected to the second discharge branch Vo4, and the second end of the second energy storage capacitor C24 is grounded GND, that is, the second end of the second energy storage capacitor C24 is also the grounding end of the second discharge branch, and together with the second discharge branch Vo4, an output loop is formed.

[0104] Figure 5 The fourth structural diagram of the switching power supply circuit provided in the embodiment of the present application is shown in FIG. Figure 5 As shown, in one embodiment, the first switch circuit S21 includes a first MOS transistor Q26, a second MOS transistor Q27, a second diode D2, a third capacitor C25 and a first resistor R1; the first MOS transistor Q26 and the second MOS transistor Q27 are a group of back-to-back MOS transistors, the first electrode of the first MOS transistor Q26 is connected to the opposite end SRV of the secondary winding, the second electrode of the first MOS transistor Q26 is connected to the second electrode of the second MOS transistor Q27, and the first electrode of the second MOS transistor Q27 is the output end of the first discharge branch Vo1; the control electrode of the first MOS transistor Q26 is connected to the secondary control circuit 22; the control electrode of the second MOS transistor Q27 is connected to the first end of the third capacitor C25, and the second end of the third capacitor C25 is connected to the secondary control circuit 22; the positive electrode of the second diode D2 is connected to the first electrode of the second MOS transistor Q27, and the negative electrode of the second diode D2 is connected to the control electrode of the second MOS transistor Q27; the first resistor R1 is connected in parallel at both ends of the second diode D2. The first electrode of the second MOS tube Q27 is connected to the output end of the first discharge branch Vo1. The voltage at the output end of the first discharge branch Vo1 does not change dramatically, so that the third capacitor can drive the third capacitor C25, the second diode D2 and the first energy storage capacitor C23 in a bootstrap manner.

[0105] In this embodiment, a second switch circuit S22 is provided on the second discharge branch Vo4. The second switch circuit includes a fourth MOS transistor Q24, a fifth MOS transistor Q25, a third diode D3, a fourth capacitor C26 and a second resistor R2. The fourth MOS transistor Q24 and the fifth MOS transistor Q25 are a group of back-to-back MOS transistors, the first electrode of the fourth MOS transistor Q24 is connected to the opposite-name end SRV of the secondary winding, the second electrode of the fourth MOS transistor Q24 is connected to the second electrode of the fifth MOS transistor Q25, and the first electrode of the fifth MOS transistor Q25 is the output end of the second discharge branch Vo4; the control electrode S221 of the fourth MOS transistor Q24 is connected to the secondary control circuit 22; the control electrode S222 of the fifth MOS transistor Q25 is connected to the first end of the fourth capacitor C26, and the second end of the fourth capacitor C26 is connected to the secondary control circuit 22; the positive electrode of the third diode D3 is connected to the first electrode of the fifth MOS transistor Q25, and the negative electrode of the third diode D3 is connected to the control electrode S222 of the fifth MOS transistor Q25; the second resistor R2 is connected in parallel to both ends of the third diode D3.

[0106] Above Figure 5 The switching power supply circuit shown is a dual-output power supply circuit structure. In the PD (Power Delivery) application scenario, since the voltage output by the first discharge branch Vo3 and the second discharge branch Vo4 needs to be adjustable, the relative magnitude of the voltage output on the first discharge branch Vo3 and the second discharge branch Vo4 will change, so the first switch circuit S21 and the second switch circuit S22 need to be able to withstand bidirectional withstand voltage. Therefore, when the first switch circuit S21 and the second switch circuit S22 of this embodiment are implemented using MOS tubes, due to the body diode, the first switch circuit S21 and the second switch circuit S22 both require two back-to-back MOS tubes, which can be specifically MOSFET tubes, GaN tubes, SiC tubes and other power devices.

[0107] Among them, the source of the first MOS tube Q26 and the fourth MOS tube Q24 is at the SRV point. When working, the voltage at the SRV point changes dynamically. Therefore, the second capacitor C22 is introduced in this embodiment to provide a BST voltage. The voltage difference between BST and SW is controlled at the value required by the circuit, and its value mainly depends on the withstand voltage and performance parameters of the driving power tube. For the second MOS tube Q27 and the fifth MOS tube Q25, their sources are respectively connected to the first discharge branch Vo3 and the second discharge branch Vo4. Since the first discharge branch Vo3 and the second discharge branch Vo4 are output ends, the voltage will not change drastically. Therefore, the second MOS tube Q27 can be driven by the second diode D2, the first energy storage capacitor C23 and the first resistor R1 in the form of bootstrap, and the fifth MOS tube Q25 can be driven by the third diode D3, the second energy storage capacitor C24 and the second resistor R2 in the form of bootstrap, which solves the technical problems of driving and power supplying the power tubes in the first switch circuit S21 and the second switch circuit S22, without the need for additional power supply and drive circuits, and saving the hardware cost of the circuit.

[0108] In one embodiment, when the outputs of the first discharge branch Vo3 and the second discharge branch Vo4 of the switching power supply circuit are two fixed voltages, and the voltage output on the first discharge branch Vo3 is always greater than the voltage output on the second discharge branch Vo4, at this time, since the voltage output on the first discharge branch Vo3 is always higher than the voltage at the SRV point, it is not necessary to block the reverse conduction of the parasitic diode of the fourth MOS tube Q24, then for Figure 5 The switching power supply shown does not need to be provided with the fifth MOS tube Q25.

[0109] Figure 6 For the fifth structural diagram of the switching power supply circuit provided in the embodiment of the present application, please refer to Figure 6 As shown, in one embodiment, a first switch circuit is provided on the first discharge branch Vo3, and the first switch circuit includes a third MOS transistor Q23, a first electrode of the third MOS transistor Q23 is connected to the opposite-name end SRV of the secondary winding, a second electrode of the third MOS transistor Q23 is an output end of the first discharge branch to output a discharge voltage, and a control electrode S213 of the third MOS transistor Q23 is connected to the secondary control circuit 22. Among them, the circuit structure of the second switch circuit S22 on the second discharge branch Vo4 is the same as that in the above embodiment, and will not be repeated here.

[0110] In some embodiments, the secondary control circuit 22 specifically includes a BST power supply unit 220, a first drive circuit 221, and a second drive circuit 222. The output end of the BST power supply unit 220 is connected to the first drive circuit 221 and the second drive circuit 222. The output end of the first drive circuit 221 is connected to the control electrode S210 of the first MOS transistor Q26, and the output end of the second drive circuit 222 is connected to the control electrode S221 of the fourth MOS transistor Q24. The BST power supply unit 220 is used to output corresponding control to control the first drive circuit 221 and the second drive circuit 222 to respectively output corresponding drive signals, and the drive signals are used to respectively drive the first MOS transistor Q26 and the fourth MOS transistor Q24 to be turned on or off.

[0111] Figure 7 For the sixth structural diagram of the switching power supply circuit provided in the embodiment of the present application, please refer to Figure 7 As shown, in one embodiment, the switching power supply circuit includes only one output, for example, the switching power supply circuit includes only the first discharge branch Vo3, then the first switching circuit S21 only needs unidirectional withstand voltage, and there is no need to set two back-to-back MOS tubes. Specifically, the first switching circuit includes a third MOS tube Q23, and the third MOS tube Q23 is an NMOS tube, whose source is connected to the opposite-name end SRV of the secondary winding, whose drain is the output end, and whose gate S213 is connected to the secondary control circuit 22.

[0112] In this embodiment, the first MOS transistor Q26, the second MOS transistor Q27, the third MOS transistor Q23, the fourth MOS transistor Q24 and the fifth MOS transistor Q25 can be NMOS (N-Metal-Oxide-Semiconductor) transistors. In other embodiments, the first MOS transistor Q23, the second MOS transistor Q24, the fourth MOS transistor Q24 and the fifth MOS transistor Q25 can also be PMOS (P-Metal-Oxide-Semiconductor) transistors. For example, when the above-mentioned MOS transistors are NMOS transistors, the first pole is the drain, the second pole is the source, and the control pole is the gate.

[0113] It should be noted that the second transistor Q21 in this embodiment adopts a low-side connection method, that is, the second transistor Q21 is between the transformer and SGND, and the second transistor Q21 plays a role of synchronous rectification. For the synchronous rectification application of the high-side connection method, the second transistor Q21 can be connected between the transformer and the SRV point. Taking the second transistor Q21 as an NMOS synchronous rectifier as an example, its drain is connected to the second transformer T2, and its source is connected to the source of the third transistor Q3.

[0114] It should be noted that, in other embodiments, the primary control circuit 21 in the present application can be understood as a primary controller, which can adopt a flyback circuit, AHB Flyback (asymmetric flyback converter), etc.; in addition, the first transistor Q1 is introduced into the primary circuit of this embodiment. In other embodiments, the first transistor Q1 can be replaced by a half-bridge control circuit or a full-bridge control circuit.

[0115] It should be noted that, in other embodiments, the switching power supply circuit may include multiple discharge branches, for example, three or four discharge branches. The structure and connection relationship of the remaining extended discharge branches refer to the second discharge branch. The secondary control circuit 22 controls the discharge voltage output by controlling the discharge duration of each discharge branch.

[0116] Figure 8 The waveform diagram of the switching power supply circuit provided in the embodiment of the present application in a working mode is as follows: Figure 8In the figure, S21 / S22 is a control signal of a group of switches, and S21 / S22 represents the control signal on the first switch circuit S21 and the second switch circuit S22, wherein when S21 / S22 is at a high level, it indicates that the first switch circuit S21 and the second switch circuit S22 are in a conducting state, or one of the first switch circuit S21 and the second switch circuit S22 is in a conducting state, at which time, the proportion of the conduction time can be controlled according to the output voltage requirements on the first discharge branch Vo3 and the second discharge branch Vo4, and the conduction time of the first switch circuit S21 and the second switch circuit S22 can be controlled according to the set proportion. In particular, when controlling the conduction time of the first switch circuit S21 and the second switch circuit S22, a dead zone may be introduced, and during the dead zone, the first switch circuit S21 and the second switch circuit S22 will be briefly turned off at the same time, that is, when S21 / S22 is at a high level, the first switch circuit S21 and the second switch circuit S22 will also be turned off at the same time. When S21 / S22 is at a low level, it indicates that the first switch circuit S21 and the second switch circuit S22 are both in the off state. Lm indicates the current signal on the transformer, and Lm0 indicates the current reference signal. D indicates the voltage waveform at point D in the primary loop, PDRV indicates the waveform on the control electrode of the first transistor Q20, PDRV is at a high level, indicating that the first transistor Q20 is turned on, and PDRV is at a low level, indicating that the first transistor Q20 is turned off; SDRV indicates the waveform on the control electrode of the second transistor Q21, SDRV is at a high level, indicating that the second transistor Q21 is turned on, and SDRV is at a low level, indicating that the second transistor Q21 is turned off. S0 indicates the waveform on the control electrode of the third transistor Q22, S0 is at a high level, indicating that the third transistor Q22 is turned on, and S0 is at a low level, indicating that the third transistor Q22 is turned off; SRD is the voltage waveform on the same-name end of the secondary winding of the second transformer T2, and VO is the reference voltage waveform.

[0117] Fig. 9 For a flowchart of the switching power supply circuit provided in an embodiment of the present application in one working mode, please refer to Figure 8 and Fig. 9 As shown, when the switching power supply circuit operates in the discontinuous conduction mode, within a working cycle, the working process of the switching power supply circuit includes:

[0118] S901, a primary control circuit is used to control the first transistor to turn on so that the current value on the transformer increases, and to turn off the first transistor after the turn-on time of the first transistor reaches a first preset time length.

[0119] See also Figure 8As shown, at time t0, when PDRV is at a high level, the first transistor Q20 is controlled to be turned on. At this time, the current Lm on the second transformer T2 will gradually increase. At this time, S21 / S22 is at a high level, and the first switch circuit S21 and the second switch circuit S22 are in the on state.

[0120] After the on time of the first transistor Q20 reaches the first preset time, the first transistor Q20 is turned off. For example, when the on time of the first transistor Q20 reaches the first preset time at time t1, the first transistor Q20 is turned off. When the first transistor Q20 is turned off, the current Lm on the second transformer T2 reaches the maximum value, the second transformer T2 transfers energy to the secondary, the voltage at the SRD point decreases, and the voltage at the SRV point increases. For different synchronous rectification control methods, the voltage of the SDRV includes two situations, one is that it can be kept constant at a high level, and the other is that the voltage of the SDRV is adjusted according to the Lm current so that the SRD is stabilized at the set value.

[0121] S902, a secondary control circuit is used to control turning on the second transistor when the first transistor is turned off.

[0122] Specifically, at time t1, the first transistor Q20 is turned off and the second transistor Q21 is turned on. After the second transistor Q21 is turned on, the current Lm on the second transformer T2 gradually decreases. When the current Lm decreases to near 0V, the second transistor Q21 is continuously turned on, and the current Lm reverses.

[0123] S903, the secondary control circuit is also used to control the discharge branch to be turned off and the third transistor to be turned on after the turn-on time of the second transistor reaches a second preset time; and to control the third transistor to be turned off and the discharge branch to be turned on and the second transistor to be turned off after the turn-on time of the third transistor reaches a third preset time.

[0124] Specifically, at time t3, the secondary control circuit 22 controls the third transistor Q22 to be turned on, and the first switch circuit S21 and the second switch circuit S22 are turned off, so that the first discharge branch Vo3 and the second discharge branch Vo4 are turned off. Before the first transistor Q20 is turned on, the reverse current on the second transformer T2 can resonate the voltage at point D (i.e., the drain of the first transistor Q20) to near 0V, thereby realizing the zero voltage switch of the first transistor Q20 and improving the working efficiency of the power supply circuit.

[0125] At time t4, after detecting that the turn-on time of the third transistor Q22 reaches the third preset time length, or detecting that the current Lm reaches the preset value, the secondary control circuit 22 controls the third transistor Q22 to be turned off, and at the same time controls the discharge branch to be turned on, and controls the second transistor Q21 to be turned off. At this time, the current Lm gradually approaches 0V.

[0126] Specifically, when the reverse inductor current of current Lm has reached the value required to satisfy the zero voltage switch-on (ZVS) of the first transistor Q2, the current Lm does not need to continue to increase in negative current. The secondary control circuit 22 actively controls the first switch circuit S21 and the second switch circuit S22 to be disconnected at the same time, and controls the third transistor Q22 to be turned on. At this time, the Lm current is negative, and the voltages at points SRV and D will drop. In order to provide high switching efficiency, the voltage at point SRV is detected, and the third transistor Q22 can be turned on after the SRV voltage drops to near the SGND voltage. At this time, since the voltage difference between the two ends of the secondary winding (SRD and SRV) is small, the voltage difference is the sum of the on-resistance of the second transistor Q21 and the third transistor Q22 multiplied by the current. Since the on-resistance is small, the voltage difference is small. It can be considered that the current change of the secondary winding is small, and the reverse current of Lm is maintained in the second transformer T2. The switching power supply circuit is approximately considered to be operating in a discontinuous conduction mode (DCM) state. When the switching power supply circuit in the related art is in this state, SRD and D points will generate an LC resonant voltage waveform, affecting the stability of the circuit, while the circuit of this embodiment can overcome this defect, so the working efficiency of the circuit can be effectively improved.

[0127] S904, the primary control circuit is further used to control turning on the first transistor after a fourth preset time period has passed after the second transistor is turned off.

[0128] At time t4, after the second transistor Q21 is turned off, due to the negative current in Lm, the voltage at point SRD will rise and the voltage at point D will drop. After the second transistor Q21 is turned off, the third transistor Q22 can be turned off immediately, and the first switch circuit S21 and the second switch circuit S22 can be turned on. However, in order to reduce the power glitch between the source and drain of the second transistor Q21 when the first transistor Q20 is turned on, the turn-off time of the third transistor Q22 and the turn-on time of S11 / S22 can be delayed after time t4. The delay time is very short. The delayed turn-on time can be but not limited to between 4t and t5, that is, the delay time is before the next turn-on time of the first transistor Q20. In this way, when the first transistor Q20 is turned on, the power supply at point SRV is approximately equal to SGND, eliminating the increase in the SRD voltage spike caused by VO. The advantage of this is that the second transistor Q21 can use a power tube with a lower withstand voltage, which can increase the efficiency.

[0129] After the fourth preset time, when the voltage at point D drops to the preset voltage, the first transistor Q20 is controlled to be turned on. At this time, when the first transistor Q20 is turned on, the voltage at point D is very low, which reduces the turn-on loss of Q10 and improves efficiency.

[0130] In one working scenario, when the first transistor Q20 is turned on, the third transistor Q22 remains turned on, and the first switch circuit S21 and the second switch circuit S22 remain turned off. At this time, the voltage at the SRV point is approximately equal to SGND, reducing the voltage spike at the SRD.

[0131] Among them, in this embodiment, each preset time can be specifically set according to the actual application scenario, and it is only necessary to ensure the above-mentioned working sequence. There is no specific limitation on each preset time here.

[0132] Fig.10 This is a waveform diagram of the switching power supply circuit provided in an embodiment of the present application in another working mode. Fig.11 For a flowchart of the switching power supply circuit provided in the embodiment of the present application in another working mode, please refer to Fig.10 and Fig.11 As shown, when the switching power supply circuit works in a DCM mode that can reduce the voltage spike at the SRD point, within a working cycle, the working process of the switching power supply circuit includes:

[0133] S111, a primary control circuit, used for controlling the first transistor to turn on so that the current value on the transformer increases, and turning off the first transistor after the turn-on time of the first transistor reaches a first preset time length.

[0134] S112, a secondary control circuit, used for controlling the second transistor to be turned on when the first transistor is turned off, and controlling the third transistor to be turned off, and controlling the discharge branch to be turned on.

[0135] S113, the secondary control circuit is further used to control turning on the third transistor and turning off the discharge branch after the closing time of the third transistor reaches a fifth preset time length.

[0136] S114, the secondary control circuit is further used to control turning off the second transistor after the turn-on time of the second transistor reaches a sixth preset time length.

[0137] S115, the primary control circuit is further used to control turning on the first transistor after a seventh preset time period has passed after the second transistor is turned off.

[0138] Among them, in this embodiment, each preset time can be specifically set according to the actual application scenario, and it is only necessary to ensure the above-mentioned working sequence. There is no specific limitation on each preset time here.

[0139] Among them, in the above working mode, the voltage and current waveforms of each point on the switching power supply circuit can be referred to Fig.10 For the specific workflow, please refer to Fig.11As shown, in this working mode, the voltage peak of the SRD point can be reduced, and the zero voltage switch of the first transistor Q20 can be realized, thereby improving the working efficiency of the power supply circuit. The specific working process can refer to the above embodiment, which will not be repeated here.

[0140] Fig.12 This is a waveform diagram of the switching power supply circuit provided in an embodiment of the present application in another working mode. Fig.13 For a flowchart of the switching power supply circuit provided in the embodiment of the present application in another working mode, please refer to Fig.12 and Fig.13 As shown, when the switching power supply circuit of this embodiment works in the continuous conduction mode, within a working cycle, the working process of the switching power supply circuit includes:

[0141] S131, a primary control circuit, used for controlling the first transistor to turn on;

[0142] S132, a secondary control circuit, used for controlling the third transistor to turn on, the second transistor to turn off, and the discharge branch to disconnect when the first transistor is turned on;

[0143] S133, the primary control circuit is further used to control the first transistor to be turned off after the turn-on time of the first transistor reaches an eighth preset time;

[0144] S134, the secondary control circuit is also used to control the third transistor to turn off, the second transistor to turn on, and the discharge branch to conduct when the first transistor is turned off.

[0145] Among them, in this embodiment, each preset time can be specifically set according to the actual application scenario, and it is only necessary to ensure the above-mentioned working sequence. There is no specific limitation on each preset time here.

[0146] Among them, in the above working mode, the voltage and current waveforms of each point on the switching power supply circuit can be referred to Fig.12 For the specific workflow, please refer to Fig.13 As shown, in this working mode, the voltage peak of the SRD point can be reduced, and the zero voltage switch of the first transistor Q20 can be realized, thereby improving the working efficiency of the power supply circuit. The specific working process can refer to the above embodiment, which will not be repeated here.

[0147] This embodiment provides a control method for a switching power supply circuit. The circuit structure of the switching power supply circuit can refer to Figure 2 The control method for the switching power supply circuit provided in this embodiment can correspond to the working process of the switching power supply circuit described above.

[0148] Fig.14One of the control method flow charts provided in the embodiment of the present application is shown in Fig.14 As shown, when the switching power supply circuit operates in a discontinuous conduction mode, within a working cycle, the control method includes:

[0149] S141, controlling the first transistor to turn on so that the current value on the transformer increases, and turning off the first transistor after the turn-on time of the first transistor reaches a first preset time length.

[0150] S142, when the first transistor is turned off, controlling to turn on the second transistor;

[0151] S143, after the turn-on time of the second transistor reaches a second preset time length, controlling the discharge branch to be turned off, and controlling the third transistor to be turned on; and after the turn-on time of the third transistor reaches a third preset time length, controlling the third transistor to be turned off, and controlling the switch circuit to turn on the discharge branch, and controlling the second transistor to be turned off;

[0152] S144, after the second transistor is turned off, after a fourth preset time period has passed, control to turn on the first transistor.

[0153] Fig.15 For the second control method flow chart provided in the embodiment of the present application, please refer to Fig.15 As shown, when the switching power supply circuit operates in another discontinuous conduction mode, the voltage peak at the SRD point can be reduced. In one working cycle, the control method includes:

[0154] S151, controlling the first transistor to turn on so that the current value on the transformer increases, and turning off the first transistor after the turn-on time of the first transistor reaches a first preset time length;

[0155] S152, when the first transistor is turned off, controlling the second transistor to be turned on, and controlling the third transistor to be turned off, and controlling the discharge branch to be turned on;

[0156] S153, after the closing time of the third transistor reaches a fifth preset time length, controlling to turn on the third transistor, and at the same time controlling the switch circuit to turn off the discharge branch;

[0157] S154, after the on time of the second transistor reaches a sixth preset time length, controlling to turn off the second transistor;

[0158] S155 , after the second transistor is turned off, after a seventh preset time period has passed, control to turn on the first transistor.

[0159] Fig.16 For the third flow chart of the control method provided in the embodiment of the present application, please refer to Fig.16As shown, when the switching power supply circuit operates in a continuous conduction mode, within a working cycle, the control method includes:

[0160] S161, controlling the first transistor to turn on;

[0161] S162, when the first transistor is turned on, controlling the third transistor to be turned on, controlling the second transistor to be turned off, and controlling the switch circuit to disconnect the discharge branch;

[0162] S163, after the turn-on time of the first transistor reaches an eighth preset time, controlling the first transistor to turn off;

[0163] S164, when the first transistor is turned off, control the third transistor to be turned off, control the second transistor to be turned on, and control the switch circuit to turn on the discharge branch.

[0164] Based on the switching power supply circuits provided in the above embodiments, this embodiment further provides a chip, which includes the switching power supply circuits provided in the above embodiments; in other words, the above switching power supply circuits are integrated into a functional chip to facilitate layout and use.

[0165] This embodiment further provides an electronic device, which includes the switching power supply circuit provided by the above embodiments; or the electronic device includes the above chip.

[0166] Finally, it should be noted that the above embodiments are only specific implementation methods of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A switching power supply circuit, characterized in that: include: A transformer, a primary control circuit, a secondary control circuit, a first transistor, a second transistor, a third transistor and at least one discharge branch; The same-name end of the primary winding of the transformer is used to receive the power supply voltage, the opposite-name end of the primary winding is connected to the first electrode of the first transistor, and the second electrode of the first transistor is grounded; the control electrode of the first transistor is connected to the primary control circuit, and the primary control circuit is used to control the conduction and shutdown of the first transistor; The opposite-name end of the secondary winding of the transformer is connected to the first electrode of the third transistor, the second electrode of the third transistor is connected to the second electrode of the second transistor, the first electrode of the second transistor is connected to the same-name end of the secondary winding, and the control electrodes of the second transistor and the third transistor are connected to the secondary control circuit, and the secondary control circuit is used to control the conduction and disconnection of the second transistor and the third transistor; The opposite-polarity end of the secondary winding of the transformer is connected to the input end of the at least one discharge branch, and the output end of the at least one discharge branch is used to output a discharge voltage; at least one switch circuit is provided on each discharge branch, and the control end of the switch circuit is also connected to the secondary control circuit; The secondary control circuit is used to control the on or off of the switch circuit on the discharge branch, thereby controlling the discharge branch to output a corresponding discharge voltage.

2. The switching power supply circuit according to claim 1, characterized in that: It also includes a first diode and a first capacitor; the positive electrode of the first diode is connected to the opposite end of the secondary winding, the negative electrode of the first diode is connected to the first end of the first capacitor, and the second end of the first capacitor is grounded; Wherein, the first end of the first capacitor is also connected to the power supply end of the secondary control circuit.

3. The switching power supply circuit according to claim 1 or 2, characterized in that: It also includes a second capacitor, a first end of which is connected to the opposite end of the secondary winding, and a second end of the second capacitor is connected to the bootstrap capacitor pin of the secondary control circuit; the first end of the second capacitor is also connected to the level switching pin of the secondary control circuit.

4. The switching power supply circuit according to claim 1 or 2, characterized in that: Each of the discharge branches includes an energy storage capacitor, a first end of the energy storage capacitor is connected to the discharge branch, and a second end of the energy storage capacitor is grounded.

5. The switching power supply circuit according to claim 1 or 2, characterized in that: An isolation circuit is also included, and the primary control circuit is connected to the secondary control circuit through the isolation circuit.

6. The switching power supply circuit according to claim 1 or 2, characterized in that: The switch circuit includes a first MOS tube, a second MOS tube, a second diode, a third capacitor and a first resistor; The first MOS transistor and the second MOS transistor are a group of back-to-back MOS transistors, the first electrode of the first MOS transistor is connected to the opposite end of the secondary winding, the second electrode of the first MOS transistor is connected to the second electrode of the second MOS transistor, and the first electrode of the second MOS transistor is the output end of the discharge branch; the control electrode of the first MOS transistor is connected to the secondary control circuit; the control electrode of the second MOS transistor is connected to the first end of the third capacitor, and the second end of the third capacitor is connected to the secondary control circuit; The anode of the second diode is connected to the first electrode of the second MOS tube, and the cathode of the second diode is connected to the control electrode of the second MOS tube; the first resistor is connected in parallel to both ends of the second diode.

7. The switching power supply circuit according to claim 1 or 2, characterized in that: It comprises two discharge branches, wherein the two discharge branches are respectively a first discharge branch and a second discharge branch; The first discharge branch is provided with a first switch circuit, the first switch circuit comprises a third MOS transistor, a first pole of the third MOS transistor is connected to the opposite end of the secondary winding, and a second pole of the third MOS transistor is the output end of the first discharge branch; The second discharge branch is provided with a second switch circuit, and the second switch circuit includes a fourth MOS transistor, a fifth MOS transistor, a third diode, a fourth capacitor and a second resistor; The fourth MOS tube and the fifth MOS tube are a group of back-to-back MOS tubes, the first electrode of the fourth MOS tube is connected to the opposite end of the secondary winding, the second electrode of the fourth MOS tube is connected to the second electrode of the fifth MOS tube, and the first electrode of the fifth MOS tube is the output end of the second discharge branch; the control electrode of the fourth MOS tube is connected to the secondary control circuit; the control electrode of the fifth MOS tube is connected to the first end of the fourth capacitor, and the second end of the fourth capacitor is connected to the secondary control circuit; the positive electrode of the third diode is connected to the first electrode of the fifth MOS tube, and the negative electrode of the third diode is connected to the control electrode of the fifth MOS tube; the second resistor is connected in parallel to both ends of the third diode.

8. The switching power supply circuit according to claim 1 or 2, characterized in that: When the switching power supply circuit operates in the first discontinuous conduction mode, within one working cycle: The primary control circuit is used to control the first transistor to turn on so that the current value on the transformer increases, and to turn off the first transistor after the turn-on time of the first transistor reaches a first preset time length; The secondary control circuit is used for controlling the second transistor to be turned on at the moment when the first transistor is turned off; The secondary control circuit is further used for controlling the discharge branch to be turned off and the third transistor to be turned on after the turn-on time of the second transistor reaches a second preset time; and controlling the third transistor to be turned off and the discharge branch to be turned on and the second transistor to be turned off after the turn-on time of the third transistor reaches a third preset time. The primary control circuit is further configured to control turning on the first transistor after a fourth preset time period has passed after the second transistor is turned off.

9. The switching power supply circuit according to claim 1 or 2, characterized in that: When the switching power supply circuit operates in the second discontinuous conduction mode, within one working cycle: The primary control circuit is used to control the first transistor to turn on so that the current value on the transformer increases, and to turn off the first transistor after the turn-on time of the first transistor reaches a first preset time length; The secondary control circuit is used for controlling the second transistor to be turned on, and the third transistor to be turned off, and the discharge branch to be turned on at the moment when the first transistor is turned off; The secondary control circuit is further used for controlling the third transistor to be turned on and the discharge branch to be turned off after the turn-off time of the third transistor reaches a fifth preset time length; The secondary control circuit is further configured to control turning off the second transistor after the on time of the second transistor reaches a sixth preset time length; The primary control circuit is further configured to control turning on the first transistor after a seventh preset time period has passed after the second transistor is turned off.

10. The switching power supply circuit according to claim 1 or 2, characterized in that: When the switching power supply circuit operates in the continuous conduction mode, within one working cycle: The primary control circuit is used to control the first transistor to turn on; The secondary control circuit is used to control the third transistor to turn on, the second transistor to turn off, and the discharge branch to disconnect when the first transistor is turned on; The primary control circuit is further configured to control the first transistor to be turned off after the on time of the first transistor reaches an eighth preset time; The secondary control circuit is further used for controlling the third transistor to be turned off, the second transistor to be turned on, and the discharge branch to be turned on when the first transistor is turned off.

11. A control method for a switching power supply circuit, characterized in that: The switching power supply circuit comprises: a transformer, a primary control circuit, a secondary control circuit, a first transistor, a second transistor, a third transistor and at least one discharge branch; the same-name end of the primary winding of the transformer is used to receive the supply voltage, the opposite-name end of the primary winding is connected to the first electrode of the first transistor, and the second electrode of the first transistor is grounded; the control electrode of the first transistor is connected to the primary control circuit; the opposite-name end of the secondary winding of the transformer is connected to the first electrode of the third transistor, the second electrode of the third transistor is connected to the second electrode of the second transistor, the first electrode of the second transistor is connected to the same-name end of the secondary winding, and the control electrodes of the second transistor and the third transistor are connected to the secondary control circuit; the first electrode of the third transistor is connected to the input end of the at least one discharge branch, and the output end of the at least one discharge branch is used to output the discharge voltage; at least one switch circuit is arranged on each discharge branch, and the control end of the switch circuit is also connected to the secondary control circuit; When the switching power supply circuit operates in a first discontinuous conduction mode, within a working cycle, the control method includes: Controlling the first transistor to turn on so that the current value on the transformer increases, and turning off the first transistor after the turn-on time of the first transistor reaches a first preset time length; At the moment of closing the first transistor, controlling to open the second transistor; After the on-time of the second transistor reaches a second preset time length, the discharge branch is controlled to be turned off, and the third transistor is controlled to be turned on at the same time; and after the on-time of the third transistor reaches a third preset time length, the third transistor is controlled to be turned off, and the switch circuit is controlled to turn on the discharge branch, and the second transistor is controlled to be turned off; After the second transistor is turned off, after a fourth preset time period, the first transistor is controlled to be turned on.

12. The control method for a switching power supply circuit according to claim 11, characterized in that: When the switching power supply circuit operates in the second discontinuous conduction mode, within a working cycle, the control method further includes: Controlling the first transistor to turn on so that the current value on the transformer increases, and turning off the first transistor after the turn-on time of the first transistor reaches a first preset time length; At the moment of closing the first transistor, controlling to open the second transistor, and controlling to close the third transistor, and controlling to turn on the discharge branch; After the closing time of the third transistor reaches a fifth preset time length, controlling to turn on the third transistor, and at the same time controlling the switch circuit to turn off the discharge branch; After the on time of the second transistor reaches a sixth preset time length, controlling to turn off the second transistor; After the second transistor is turned off, after a seventh preset time period, the first transistor is controlled to be turned on.

13. The control method for a switching power supply circuit according to claim 11 or 12, characterized in that: When the switching power supply circuit operates in a continuous conduction mode, within a working cycle, the control includes: Controlling the first transistor to turn on; At the moment when the first transistor is turned on, controlling the third transistor to be turned on, controlling the second transistor to be turned off, and controlling the switch circuit to disconnect the discharge branch; After the turn-on time of the first transistor reaches an eighth preset time, controlling the first transistor to turn off; At the moment when the first transistor is turned off, the third transistor is controlled to be turned off, the second transistor is controlled to be turned on, and the switch circuit is controlled to turn on the discharge branch.

14. A chip, characterized in that: Comprising a switching power supply circuit as described in any one of claims 1-10.

15. An electronic device, characterized in that: Includes the switching power supply circuit as described in any one of claims 1 to 10; or includes the chip as described in claim 14.

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