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 and at least two discharge branches, and the secondary control circuit is used for firstly controlling a first transistor on a first discharge branch to be turned off and a second transistor on the first discharge branch to be turned on, so that the first discharge branch discharges outwards through a body diode of the first transistor and the second transistor; before the second transistor is turned off, the fourth transistor is controlled to be turned on, so that the second discharge branch discharges outwards through the body diode of the third transistor and the fourth transistor; and finally, the second transistor is controlled to be switched off and the third transistor is controlled to be switched on in sequence, so that the second discharge branch discharges outwards. Thus, in the switching process of the two discharge branches, one discharge branch is always in a conducting state to absorb excess energy output by the secondary winding, and the situation that the circuit is damaged due to the fact that voltage spikes are generated is avoided.

Description

Technical Field

[0001] This application relates to the field of switching power supply technology, and in particular to a switching power supply circuit and its control method, chip, and electronic device. Background Technology

[0002] With the development of fast charging technology, power adapters with high power, small size, and multiple outputs have become a trend. In the existing field of multi-output fast charging adapters, related technologies provide a dual-output isolated power supply system. This dual-output isolated power supply system includes a transformer, with both output paths located on the secondary side of the transformer. Each output path has two transistors arranged back-to-back to form an on / off switch, enabling the two transistors to withstand voltage bidirectionally to prevent energy leakage during output switching. For any output path, a drive signal is used to simultaneously control the two transistors on that output path to turn on or off, thereby controlling the secondary circuit to alternately supply power to multiple output paths.

[0003] In related technologies, to prevent the switches on two output paths from opening simultaneously and directly connecting the two different output paths, thus damaging the system, two control signals need to have a period during the switching time when the switches are switched off simultaneously. This period is called the dead time. During the dead time, the energy on the secondary side of the transformer cannot be conducted to either output path. Thus, the energy output from the transformer's secondary winding has nowhere to dissipate, and this undissipated energy will generate voltage spikes that damage the power supply circuit system. Summary of the Invention

[0004] This application provides a switching power supply circuit and its control method, chip, and electronic device to solve the technical problem in the related art where voltage spikes occur during the dead time, damaging the power supply circuit system.

[0005] In a first aspect, this application provides a switching power supply circuit, which includes: a transformer, a primary control circuit, a secondary control circuit, and at least two discharge branches; the primary control circuit is disposed in the primary winding circuit of the transformer to control the primary winding to store and release energy; the input terminal of the discharge branch is connected to the output terminal of the secondary winding circuit of the transformer, and the output terminal of the discharge branch is used to output a discharge voltage.

[0006] The secondary control circuit is used to control the conduction and cutoff of each discharge branch, thereby controlling the output state switching between the secondary winding and each discharge branch.

[0007] Specifically, for any first discharge branch and second discharge branch among the at least two discharge branches, the first discharge branch includes a first transistor and a second transistor arranged back to back, and the second discharge branch includes a third transistor and a fourth transistor arranged back to back; the control electrodes of the first transistor, the second transistor, the third transistor, and the fourth transistor are all connected to the secondary control circuit.

[0008] Specifically, when controlling the output state switching of the first discharge branch and the second discharge branch, the secondary control circuit is used to: firstly, control the first transistor on the first discharge branch to turn off and the second transistor to turn on, so that the first discharge branch discharges to the outside through the body diode of the first transistor; then, before the second transistor turns off, control the fourth transistor to turn on, so that the second discharge branch discharges to the outside through the body diode of the third transistor and the fourth transistor; finally, control the second transistor to turn off and control the third transistor to turn on in sequence, so that the second discharge branch discharges to the outside through the third transistor and the fourth transistor.

[0009] In one possible design, the switching power supply circuit further includes multiple voltage sampling circuits, each of which is used to sample the discharge voltage on a corresponding discharge branch.

[0010] The secondary control circuit is also used to acquire multiple discharge voltages on all discharge branches, sort the voltage values ​​of the multiple discharge voltages from low to high, and, during the energy release phase, sequentially control the multiple discharge branches to conduct in order of the discharge voltages from low to high to discharge to the outside.

[0011] In one possible design, the switching power supply circuit further includes at least one comparator, which is used to sample the discharge voltages corresponding to any two discharge branches and compare the voltage values ​​of the discharge voltages to output the comparison result to the secondary control circuit.

[0012] In one possible design, the discharge branch further includes an energy storage capacitor, the first end of which is connected to the high-voltage end of the discharge branch, and the second end of which is grounded.

[0013] In one possible design, the switching power supply circuit further includes an isolation circuit, through which the primary control circuit is connected to the secondary control circuit.

[0014] In one possible design, the switching power supply circuit further includes a rectifier circuit, the input terminal of which is connected to the output terminal of the secondary winding of the transformer, and the output terminal of which is connected to the input terminal of the discharge branch.

[0015] The rectifier circuit is used to rectify the AC power output from the secondary winding and output the corresponding DC power.

[0016] Secondly, this application also provides a control method for a switching power supply circuit. The switching power supply circuit includes a transformer, a primary control circuit, a secondary control circuit, and at least two discharge branches. The primary control circuit is disposed in the primary winding circuit of the transformer to control the primary winding to store and release energy. The input terminal of each discharge branch is connected to the output terminal of the secondary winding circuit of the transformer, and the output terminal of the discharge branch is used to output a discharge voltage. The secondary control circuit is used to control the conduction and cutoff of each discharge branch, thereby controlling the output state switching between the secondary winding and each discharge branch.

[0017] Specifically, for any first discharge branch and second discharge branch among the at least two discharge branches, the first discharge branch includes a first transistor and a second transistor arranged back to back, and the second discharge branch includes a third transistor and a fourth transistor arranged back to back.

[0018] During an energy release cycle, when the output state of the first discharge branch and the second discharge branch switches, the control method includes:

[0019] The first transistor in the first discharge branch is turned off and the second transistor is turned on, so that the first discharge branch discharges to the outside through the body diode of the first transistor;

[0020] Before the second transistor is turned off, the fourth transistor is controlled to be turned on, so that the second discharge branch discharges to the outside through the body diode of the third transistor and the fourth transistor;

[0021] After the fourth transistor is turned on, the second transistor is turned off and the third transistor is turned on in sequence, so that the second discharge branch discharges to the outside through the third transistor and the fourth transistor.

[0022] In one possible design, the control method further includes: acquiring multiple discharge voltages on all discharge branches, sorting the voltage values ​​of the multiple discharge voltages from low to high, and, during the energy release phase, sequentially controlling the multiple discharge branches to conduct in order of the discharge voltages from low to high to discharge to the outside.

[0023] Thirdly, this application also provides a chip that includes a switching power supply circuit as described in any of the preceding claims.

[0024] Fourthly, this application also provides an electronic device that includes a switching power supply as described in any of the preceding claims; or includes a chip as described above.

[0025] The switching power supply circuit provided in the first aspect above includes: a transformer, a primary control circuit, a secondary control circuit, and at least two discharge branches. The primary control circuit is disposed in the primary winding circuit of the transformer to control the primary winding for energy storage and release. The input terminal of the discharge branch is connected to the output terminal of the secondary winding circuit of the transformer, and the output terminal of the discharge branch is used to output a discharge voltage. The secondary control circuit is used to control the conduction and cutoff of each discharge branch, thereby controlling the output state switching between the secondary winding and each discharge branch. Specifically, for any first discharge branch and second discharge branch among the at least two discharge branches, the first discharge branch includes a first transistor and a... The second transistor, the second discharge branch, includes a third transistor and a fourth transistor arranged back-to-back. When switching the output state of the first and second discharge branches, the secondary control circuit first controls the first transistor in the first discharge branch to turn off and the second transistor to turn on, allowing the first discharge branch to discharge externally through the body diode of the first transistor and the second transistor. Then, before the second transistor turns off, it controls the fourth transistor to turn on, allowing the second discharge branch to discharge externally through the body diode of the third transistor and the fourth transistor. Finally, it sequentially controls the second transistor to turn off and the third transistor to turn on, allowing the second discharge branch to discharge externally through the third transistor and the fourth transistor. In this way, during the switching process of the two discharge branches, one discharge branch is always in a conducting state to absorb excess energy output from the secondary winding, avoiding the technical problem of voltage spikes damaging the power supply circuit system.

[0026] The beneficial effects provided by the other aspects and the various possible designs of the other aspects can be found in the beneficial effects of the first aspect and the various possible implementations of the first aspect, and will not be repeated here. Attached Figure Description

[0027] Figure 1 A schematic diagram of a dual-output isolated power supply circuit provided for related technologies;

[0028] Figure 2 A schematic diagram of the drive signal waveform when the dual-output isolated power supply circuit provided for related technologies is in operation;

[0029] Figure 3 A schematic diagram of a dual-output switching power supply circuit provided in an embodiment of this application;

[0030] Figure 4 A waveform diagram of some signals during the operation of the switching power supply circuit provided in the embodiments of this application;

[0031] Figure 5A schematic diagram of the waveforms of each control signal when the dual-output switching power supply circuit provided in the embodiments of this application is in operation;

[0032] Figure 6 One of the schematic diagrams showing the current flow direction during operation of the dual-output switching power supply circuit provided in the embodiments of this application;

[0033] Figure 7 A second schematic diagram showing the current flow direction during operation of the dual-output switching power supply circuit provided in this application embodiment;

[0034] Figure 8 The third schematic diagram of the current flow direction during operation of the dual-output switching power supply circuit provided in the embodiments of this application;

[0035] Figure 9 The fourth schematic diagram of the current flow direction during operation of the dual-output switching power supply circuit provided in the embodiments of this application;

[0036] Figure 10 Fifth schematic diagram of the current flow direction during operation of the dual-output switching power supply circuit provided in the embodiments of this application;

[0037] Figure 11 A flowchart of a control method for a switching power supply circuit provided in an embodiment of this application. Detailed Implementation

[0038] In this application, "at least one" means one or more, and "more than one" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c alone can mean: a alone, b alone, c alone, a combination of a and b, a combination of a and c, a combination of b and c, or a, b, and c, where a, b, and c can be single or multiple. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0039] The terms “center,” “longitudinal,” “lateral,” “up,” “down,” “left,” “right,” “front,” and “rear,” etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0040] The terms "connected" and "connected" should be interpreted broadly. For example, in circuit structures, "connected" or "connected" can refer not only to physical connections but also to electrical or signal connections. This could be a direct connection (physical connection) or an indirect connection via at least one intermediate component, as long as the circuit is connected. It could also refer to the internal connection between two components. Similarly, a signal connection can refer to a connection via a circuit or a medium, such as radio waves. Those skilled in the art will understand the specific meaning of these terms in this application based on the specific circumstances.

[0041] The transistor in this application is a three-terminal transistor, with its three terminals being a control terminal, a first terminal, and a second terminal. The transistor can be a bipolar transistor (BPT) or a field-effect transistor (FET), etc. For example, when the transistor is a BPT, its control terminal is the base of the BPT, the first terminal can be the collector or emitter of the BPT, and the corresponding second terminal can be the emitter or collector of the BPT; when the transistor is a FET, its control terminal is the gate of the FET, the first terminal can be the drain or source of the FET, and the corresponding second terminal can be the source or drain of the FET. Furthermore, the transistor provided in this application is not limited to MOSFETs; it can also be a fully controllable device such as GaN.

[0042] With the development of electronic technology, various types of electronic devices have emerged. Different types of electronic devices may have different charging interface types. In order to meet the charging needs of electronic devices with different interface types, power adapters can usually be set with two or more different charging interfaces, with each charging interface corresponding to a discharge branch. This can satisfy the simultaneous charging of electronic devices with different charging interfaces.

[0043] Related technology provides an isolated power supply system with dual outputs. The dual output isolated power supply system includes a transformer, and two output paths are both located on the secondary side of the transformer. Each output path has two transistors arranged back to back to form an on / off switch, so that the two transistors can withstand voltage bidirectionally to prevent energy from flowing into each other during the output switching process. For any output path, a drive signal is used to simultaneously control the two transistors on the output path to be turned on or off at the same time, thereby controlling the secondary circuit to supply power to multiple output paths in turn.

[0044] Figure 1 Please refer to the schematic diagram of the dual-output isolated power supply circuit provided for related technologies. Figure 1As shown, the dual-output isolated power supply circuit in the related technology includes a first transformer T1, a first synchronous rectifier circuit 14, a first output path Vo11, a second output path Vo12, a primary control unit 11, an isolation unit 12, and a secondary control unit 13. The input terminal of the primary winding of the first transformer T1 is used to receive a first input voltage VIN1. The primary winding is coupled to the secondary winding to transfer the electrical energy of the received first input voltage VIN1 to the secondary winding circuit. The two output terminals of the secondary winding of the first transformer T1... The same-name terminal and the opposite-name terminal are respectively connected to the input terminal of the first synchronous rectifier circuit 14. The output terminal of the first synchronous rectifier circuit 14 is respectively connected to the input terminal of the first output path Vo11 and the input terminal of the second output path Vo12. The first synchronous rectifier circuit 14 is used to rectify the AC power received by the secondary winding to output the rectified first DC power Vo-Pre1 to the first output path Vo11 and the second output path Vo12. The output terminal of the first output path Vo11 and the output terminal of the second output path Vo12 are respectively used to output different voltage signals.

[0045] Specifically, the first output path Vo11 includes the thirty-first transistor Q31, the thirty-second transistor Q32, and the first capacitor C1. In this embodiment, both the thirty-first transistor Q31 and the thirty-second transistor Q32 can be PMOS (P-Metal-Oxide-Semiconductor) transistors. The thirty-first transistor Q31 and the thirty-second transistor Q32 are arranged back to back so that the two transistors can withstand voltage bidirectionally to prevent energy from flowing back into each other during the output switching process. Specifically, the source of the thirty-first transistor Q31 is the input terminal of the first output path Vo11, used to receive the rectified first DC voltage Vo-Pre1 output by the first synchronous rectifier circuit 14. The source of the thirty-first transistor Q31 is connected to the output terminal of the first synchronous rectifier circuit 14. The drain of the thirty-first transistor Q31 is connected to the drain of the thirty-second transistor Q32. The source of the thirty-second transistor Q32 is the output terminal of the first output path Vo11, used to output the first voltage signal. The source of the thirty-second transistor Q32 is connected to the first terminal of the first capacitor C1, and the second terminal of the first capacitor C1 is grounded to GND. It is understandable that when both the thirty-first transistor Q31 and the thirty-second transistor Q32 are in the on state, the rectified first DC power Vo-Pre1 output by the first synchronous rectifier circuit 14 can be powered through the output terminal of the first output path Vo11, so that the first output path Vo11 outputs a set first voltage signal to charge the electronic device connected to the output terminal of the first output path Vo11. Furthermore, when both the thirty-first transistor Q31 and the thirty-second transistor Q32 are in the on state, the rectified first DC power output by the first synchronous rectifier circuit 14... The current Vo-Pre1 can simultaneously charge the first capacitor C1, allowing it to store energy. When both the thirty-first transistor Q31 and the thirty-second transistor Q32 are off, the power supply circuit switches to the second output path Vo12. At this time, the rectified first DC current Vo-Pre1 output by the synchronous rectifier circuit 14 will no longer directly supply power to the first output path Vo11. The first capacitor C1 then starts to work, releasing the pre-stored electrical energy to the output terminal, so that the electronic devices on the first output path Vo11 can continue to be charged.

[0046] Specifically, the second output path Vo12 includes the thirty-third transistor Q33, the thirty-fourth transistor Q34, and the second capacitor C2. In this embodiment, both the thirty-third transistor Q33 and the thirty-fourth transistor Q34 can be PMOS (P-Metal-Oxide-Semiconductor) transistors. The thirty-third transistor Q33 and the thirty-fourth transistor Q34 are arranged back to back so that the two transistors can withstand voltage bidirectionally to prevent energy from flowing back into each other during the output switching process. Specifically, the source of the thirty-third transistor Q33 is the input terminal of the second output path Vo12, used to receive the rectified first DC voltage Vo-Pre1 output by the first synchronous rectifier circuit 14. The source of the thirty-third transistor Q33 is connected to the output terminal of the first synchronous rectifier circuit 14. The drain of the thirty-third transistor Q33 is connected to the drain of the thirty-fourth transistor Q34. The source of the thirty-fourth transistor Q34 is the output terminal of the second output path Vo12, used to output the second voltage signal. The source of the thirty-fourth transistor Q34 is connected to the first terminal of the second capacitor C2, and the second terminal of the second capacitor C2 is grounded to GND. It is understandable that when both the thirty-third transistor Q33 and the thirty-fourth transistor Q34 are in the on state, the rectified first DC voltage Vo-Pre1 output by the first synchronous rectifier circuit 14 can be powered through the output terminal of the second output path Vo12, so that the second output path Vo12 outputs a set second voltage signal to charge the electronic device connected to the output terminal of the second output path Vo12. Furthermore, when both the thirty-third transistor Q33 and the thirty-fourth transistor Q34 are in the on state, the rectified first DC voltage output by the first synchronous rectifier circuit 14... The current Vo-Pre1 can simultaneously charge the second capacitor C2, allowing it to store energy. When both the thirty-third transistor Q33 and the thirty-fourth transistor Q34 are off, the power supply circuit switches to the first output path Vo11. At this time, the rectified first DC current Vo-Pre1 output by the synchronous rectifier circuit 14 will no longer directly supply power to the second output path Vo12. The second capacitor C2 then starts working, releasing the pre-stored electrical energy to the output terminal, so that the electronic devices on the second output path Vo12 can continue to be charged.

[0047] In this circuit, the gates of both the thirty-first transistor Q31 and the thirty-second transistor Q32 are connected to the secondary control unit 13. The secondary control unit 13 outputs a first drive signal S1 to simultaneously control the on and off states of both transistors Q31 and Q32, thereby controlling the on or off state of the first synchronous rectifier circuit 14 and the first output path Vo11. Similarly, the gates of both the thirty-third transistor Q33 and the thirty-fourth transistor Q34 are connected to the secondary control unit 13. The secondary control unit 13 outputs a second drive signal S2 to simultaneously control the on and off states of both transistors Q33 and Q34, thereby controlling the on or off state of the first synchronous rectifier circuit 14 and the second output path Vo12.

[0048] Please continue reading Figure 1 As shown, the dual-output isolated power supply circuit also includes a primary transistor Q35, a first diode D1, a third capacitor C3, and a first resistor R1. The primary transistor Q35 is disposed in the primary winding circuit of the first transformer T1. By controlling the on / off state of the primary transistor Q35, the conduction and off state of the primary winding circuit of the first transformer T1 can be controlled. Specifically, the primary transistor Q35 can be a PMOS (P-Metal-Oxide-Semiconductor) transistor. The source of the primary transistor Q35 is grounded to GDN, the gate of the primary transistor Q35 is connected to the primary control unit 11, and the drain of the primary transistor Q35 is connected to the opposite-name terminal of the primary winding of the first transformer T1. The same-name terminal of the primary winding of the first transformer T1 is used to receive the first input voltage VIN1. The anode of the first diode D1 is connected to the opposite terminal of the primary winding of the first transformer T1, and the cathode of the first diode D1 is connected to the first terminal of the third capacitor C3. The second terminal of the third capacitor C3 is connected to the same terminal of the primary winding of the first transformer T1. The first resistor R1 is connected in parallel across the third capacitor C3. The third capacitor C3 also serves as an energy storage capacitor. When the primary winding circuit of the first transformer T1 is turned on, the first input voltage VIN1 supplies power to the primary winding and simultaneously charges the third capacitor C3. The primary control unit 11 outputs a drive signal PDRV1 to control the on and off states of the primary transistor Q35, thereby controlling the on or off states of the primary winding circuit of the first transformer T1. It can be understood that when the primary control unit 11 outputs a drive signal to turn off the primary transistor Q35, the third capacitor C3, the first resistor R1, the primary winding, and the first diode D1 form a discharge circuit to release the energy stored in the third capacitor C3.

[0049] Figure 2 Please refer to the schematic diagram of the drive signal waveforms during operation of the dual-output isolated power supply circuit provided for related technologies. Figure 2 As shown, S1 is a waveform diagram of the first drive signal used to control the thirty-first transistor Q31 and the thirty-second transistor Q32, S2 is a waveform diagram of the second drive signal used to control the thirty-third transistor Q33 and the thirty-fourth transistor Q34, Vo-Pre1 is a waveform diagram of the rectified first DC voltage Vo-Pre1 output by the synchronous rectifier circuit 14, Vo111 is the output voltage set on the first output path Vo11, and Vo112 is the output voltage set on the second output path Vo12.

[0050] In one embodiment, at time t1, the first drive signal S1 output by the secondary control unit 13 is high to control the thirty-first transistor Q31 and the thirty-second transistor Q32 to be in the conducting state. At this time, the output terminal of the synchronous rectification circuit 14 is connected to the first output path Vo11. During the time period t1-t2, the rectified first DC power Vo-Pre1 output by the synchronous rectification circuit 14 supplies power to the first output path Vo11. At time t2, the first drive signal S1 output by the secondary control unit 13 flips to low to control the thirty-first transistor Q31 and the thirty-second transistor Q32 to be in the off state. At this time, the output terminal of the synchronous rectification circuit 14 is turned off from the first output path Vo11. After a delay, at time t3, the second drive signal S2 output by the secondary control unit 13 is high, controlling the thirty-third transistor Q33 and the thirty-fourth transistor Q34 to be in the conducting state. At this time, the output terminal of the synchronous rectifier circuit 14 is connected to the second output path Vo12, thus completing the output state switching, i.e., switching from the first output path Vo11 to the second output path Vo12. During the time period t3-t4, the rectified first DC power Vo-Pre1 output by the synchronous rectifier circuit 14 supplies power to the second output path Vo12. At time t4, the second drive signal S2 output by the secondary control unit 13 flips to low, controlling the thirty-third transistor Q33 and the thirty-fourth transistor Q34 to be in the off state. At this time, the output terminal of the synchronous rectifier circuit 14 is turned off from the second output path Vo12. After a delay, at time t5, the first drive signal S1 output by the secondary control unit 13 flips to high, controlling the thirty-first transistor Q31 and the thirty-second transistor Q32 to be in the conducting state, completing the output state switching again.

[0051] Since both turning a transistor on and off require a process, to prevent the transistors on both output paths from turning on simultaneously, which would directly connect the first output path Vo11 and the second output path Vo12 and damage the circuit system, the two drive signals need a time during the switching period to simultaneously turn off the switch. This time is called the dead time. Figure 2As shown, before the secondary control unit 13 controls the activation of the 33rd transistor Q33 and the 34th transistor Q34, during the time period t2-t3, the first drive signal S1 and the second drive signal S2 output by the secondary control unit 13 are both at a low level. At this time, the 31st transistor Q31, the 32nd transistor Q32, the 33rd transistor Q33, and the 34th transistor Q34 are all in the off state. The time periods t2-t3 and t4-t5 are referred to as the dead time. It should be noted that during the dead time, the voltage of the first DC voltage Vo-Pre1 output by the synchronous rectifier circuit 14 will no longer be controlled by the synchronous rectifier circuit 14, but will be affected by the output voltages on the first output path Vo11 and the second output path Vo12. Please refer to [link to relevant documentation]. Figure 2 As shown, when the output path switches from the first output path Vo11 to the second output path Vo12, if there is no energy accumulation at the output terminal of the synchronous rectifier circuit 14, the voltage value of the first DC voltage Vo-Pre1 at the output terminal of the synchronous rectifier circuit 14 should be the voltage value Vo112 set on the second output path Vo12. However, during the dead time period t2-t3, due to the energy accumulation at the output terminal of the synchronous rectifier circuit 14, the voltage value of the first DC voltage Vo-Pre1 will be pulled up by the energy accumulated during the dead time to a value higher than the voltage value Vo112 set on the second output path Vo12. Similarly, during the dead time period t4-t5, due to the energy accumulation at the output terminal of the synchronous rectifier circuit 14, the voltage value of the first DC voltage Vo-Pre1 will be pulled up by the energy accumulated during the dead time to a value higher than the voltage value Vo112 set on the second output path Vo12. During the dead time, the energy on the secondary side of the transformer cannot be conducted to either the first output path Vo11 or the second output path Vo12. As a result, the energy output from the secondary winding of the transformer has nowhere to be released, and the unreleased energy will generate voltage spikes that damage the power supply circuit system.

[0052] To overcome the deficiencies in the aforementioned related technologies, this application provides a switching power supply circuit, which includes: a transformer, a primary control circuit, a secondary control circuit, and at least two discharge branches. The primary control circuit is disposed in the primary winding circuit of the transformer to control the primary winding for energy storage and release. The input terminal of the discharge branch is connected to the output terminal of the secondary winding circuit of the transformer, and the output terminal of the discharge branch is used to output a discharge voltage. The secondary control circuit is used to control the conduction and cutoff of each discharge branch, thereby controlling the output state switching between the secondary winding and each discharge branch. For the two transistors on each discharge branch, the secondary control circuit outputs two control signals to control them separately. When switching the discharge state from one discharge branch to another, the two transistors on each discharge branch are not turned off simultaneously. Instead, one transistor is turned off first, allowing the electrical signal to conduct through the body diode of one transistor and the other transistor, thereby achieving continuous current flow. This cleverly handles the dead time, ensuring that the energy on the secondary side can always be absorbed by the output channel, avoiding the use of energy absorption circuits and potential system risks.

[0053] Specifically, for any first and second discharge branches in at least two discharge branches, the first discharge branch includes a first transistor and a second transistor arranged back-to-back, and the second discharge branch includes a third transistor and a fourth transistor arranged back-to-back. When controlling the output state switching of the first and second discharge branches, the secondary control circuit is used to: firstly, control the first transistor on the first discharge branch to turn off and the second transistor to turn on, so that the first discharge branch discharges externally through the body diode of the first transistor and the second transistor; then, before the second transistor turns off, control the fourth transistor to turn on, so that the second discharge branch discharges externally through the body diode of the third transistor and the fourth transistor; finally, control the second transistor to turn off and the third transistor to turn on sequentially, so that the second discharge branch discharges externally through the third transistor and the fourth transistor. In this way, during the switching process of the two discharge branches, one discharge branch is always in a conducting state to absorb excess energy output from the secondary winding, avoiding the technical problem of voltage spikes damaging the power supply circuit system.

[0054] The following uses a switching power supply circuit with two outputs as an example to further explain the structure and control method of the switching power supply circuit provided in this application. It should be understood that the following is only an example of a switching power supply circuit with two outputs, and is not limited to the switching power supply circuit provided in this application only having two outputs. In specific application scenarios, it can be extended to a switching power supply circuit with more than two outputs as needed.

[0055] Figure 3 For a schematic diagram of the dual-output switching power supply circuit structure provided in the embodiments of this application, please refer to [link / reference]. Figure 3 As shown, the switching power supply circuit includes: a second transformer T2, a primary control circuit 21, a secondary control circuit 23, and two discharge branches. The primary control circuit 21 is located in the primary winding circuit of the second transformer T2 to control the primary winding to store and release energy. The input terminal of the discharge branch is connected to the output terminal of the secondary winding circuit of the second transformer T2, and the output terminal of the discharge branch is used to output the discharge voltage. The secondary control circuit 23 is used to control the conduction and cutoff of each discharge branch, thereby controlling the output state switching between the secondary winding and each discharge branch.

[0056] Specifically, the two discharge branches are designated as the first discharge branch Vo1 and the second discharge branch Vo2. The first discharge branch Vo1 includes a first transistor Q11 and a second transistor Q12 arranged back-to-back, and the second discharge branch Vo2 includes a third transistor Q21 and a fourth transistor Q22 arranged back-to-back. In this embodiment, the first transistor Q11, the second transistor Q12, the third transistor Q21, and the fourth transistor Q22 are all PMOS (P-Metal-Oxide-Semiconductor) transistors.

[0057] In the switching of the output state of the first discharge branch Vo1 and the second discharge branch Vo2, the secondary control circuit 23 is used to: firstly, turn off the first transistor Q11 and turn on the second transistor Q12 on the first discharge branch Vo1, so that the first discharge branch Vo1 discharges to the outside through the body diode of the first transistor Q11 and the second transistor Q12; then, before the second transistor Q12 turns off, turn on the fourth transistor Q22, so that the second discharge branch Vo2 discharges to the outside through the body diode of the third transistor Q21 and the fourth transistor Q22; finally, turn off the second transistor Q12 and turn on the third transistor Q21 in sequence, so that the second discharge branch Vo2 discharges to the outside through the third transistor Q21 and the fourth transistor Q22. In this way, during the switching process of the two discharge branches, one discharge branch is always in the conducting state to absorb the excess energy output from the secondary winding, avoiding the technical problem of voltage spikes damaging the power supply circuit system.

[0058] In one embodiment of this application, please continue to refer to Figure 3 As shown, the two output terminals (same-name terminal and opposite-name terminal) of the secondary winding of the second transformer T2 are connected to the input terminals of the second rectifier circuit 24. The second rectifier circuit 24 is used to synchronously rectify the AC power output from the secondary winding of the second transformer T2 to obtain the rectified second DC power Vo-Pre2. The input terminal of each discharge branch is connected to the output terminal of the second rectifier circuit 24, and the output terminal of the discharge branch is used to connect to electronic equipment.

[0059] Specifically, the source of the first transistor Q1 is the input terminal of the first discharge branch Vo1, and the source of the first transistor Q1 is connected to the output terminal of the second rectifier circuit 24. The drain of the first transistor Q1 is connected to the drain of the second transistor Q12, and the source of the second transistor Q12 is the output terminal of the first discharge branch Vo1. The output terminal of the first discharge branch Vo1 is used to output the first discharge voltage Vo11 to charge the electronic device. The gates of the first transistor Q1 and the second transistor Q12 are both connected to the secondary control circuit 23. Circuit 23 can output a first control signal S11 to the first transistor Q11. The first control signal S11 is used to control the turn-on and turn-off of the first transistor Q11. For example, when the first control signal S11 output by the secondary control circuit 23 to the gate of the first transistor Q11 is high, the first control signal S11 controls the first transistor Q11 to turn on; correspondingly, when the first control signal S11 output by the secondary control circuit 23 to the gate of the first transistor Q11 is low, the first control signal S11 controls the first transistor Q11 to turn off. The secondary control circuit 23 can output a second control signal S12 to the second transistor Q12. The second control signal S12 is used to control the turn-on and turn-off of the second transistor Q12. For example, when the second control signal S12 output by the secondary control circuit 23 to the gate of the second transistor Q12 is at a high level, the second control signal S12 controls the second transistor Q12 to turn on; correspondingly, when the second control signal S12 output by the secondary control circuit 23 to the gate of the second transistor Q12 is at a low level, the second control signal S12 controls the second transistor Q12 to turn off.

[0060] In this circuit, the source of the third transistor Q21 is the input terminal of the second discharge branch Vo2, and the source of the third transistor Q21 is connected to the output terminal of the second rectifier circuit 24. The drain of the third transistor Q21 is connected to the drain of the fourth transistor Q22, and the source of the fourth transistor Q22 is the output terminal of the second discharge branch Vo2. The output terminal of the second discharge branch Vo2 is used to output the second discharge voltage Vo21 to charge the electronic device. The gates of the third transistor Q21 and the fourth transistor Q22 are both connected to the secondary control circuit 23. The control circuit 23 can output a third control signal S21 to the third transistor Q21. The third control signal S31 is used to control the turn-on and turn-off of the third transistor Q21. For example, when the third control signal S21 output by the secondary control circuit 23 to the gate of the third transistor Q21 is high, the third control signal S31 controls the third transistor Q21 to turn on; correspondingly, when the third control signal S21 output by the secondary control circuit 23 to the gate of the third transistor Q21 is low, the third control signal S21 controls the third transistor Q21 to turn off. The secondary control circuit 23 can output a fourth control signal S22 to the fourth transistor Q22. The fourth control signal S22 is used to control the turn-on and turn-off of the fourth transistor Q22. For example, when the fourth control signal S22 output by the secondary control circuit 23 to the gate of the fourth transistor Q22 is at a high level, the fourth control signal S22 controls the fourth transistor Q22 to turn on; correspondingly, when the fourth control signal S22 output by the secondary control circuit 23 to the gate of the fourth transistor Q22 is at a low level, the fourth control signal S22 controls the fourth transistor Q22 to turn off.

[0061] In one embodiment of this application, each discharge branch also includes an energy storage capacitor. The first end of the energy storage capacitor is connected to the high-voltage end in the discharge branch, and the second end of the energy storage capacitor is grounded. When the current discharge branch is connected to the output of the second rectifier circuit 24, the second DC current Vo-Pre2 output by the second rectifier circuit 24 can supply power to the discharge branch and charge the energy storage capacitor on the discharge branch so that the energy storage capacitor can store energy. When switching to other discharge branches for power supply, that is, after the output of the second rectifier circuit 24 is disconnected from the current discharge branch, the energy storage capacitor on the current discharge branch discharges to the outside to supply power to the electronic equipment at the output of the discharge branch.

[0062] In one embodiment of this application, please continue to refer to Figure 3 As shown, the first discharge branch Vo1 also includes a first energy storage capacitor C11, the source of the second transistor Q12 is connected to the first terminal of the first energy storage capacitor C11, and the second terminal of the first energy storage capacitor C11 is grounded. The second discharge branch Vo2 also includes a second energy storage capacitor C12, the source of the fourth transistor Q12 is connected to the first terminal of the second energy storage capacitor C12, and the second terminal of the second energy storage capacitor C12 is grounded.

[0063] Please continue reading Figure 3 As shown, the switching power supply circuit also includes a fifth transistor Q23, a second diode D2, a third energy storage capacitor C13, and a second resistor R2. The fifth transistor Q23 is located in the primary winding circuit of the second transformer T2. By controlling the on / off state of the fifth transistor Q23, the conduction and off state of the primary winding circuit of the second transformer T2 can be controlled. Specifically, the fifth transistor Q23 can be a PMOS (P-Metal-Oxide-Semiconductor) transistor. The source of the fifth transistor Q23 is grounded to GDN, the gate of the fifth transistor Q23 is connected to the primary control circuit 21, and the drain of the fifth transistor Q23 is connected to the opposite-name terminal of the primary winding of the second transformer T2. The same-name terminal of the primary winding of the second transformer T2 is used to receive the second input voltage VIN2. The positive terminal of the second diode D2 is connected to the opposite terminal of the primary winding of the second transformer T2, and the negative terminal of the second diode D2 is connected to the first terminal of the third energy storage capacitor C13. The second terminal of the third energy storage capacitor C13 is connected to the same terminal of the primary winding of the second transformer T2. The second resistor R2 is connected in parallel across the third energy storage capacitor C13. The third energy storage capacitor C13 is also primarily used for energy storage. When the primary winding circuit of the second transformer T2 is turned on, the second input voltage VIN2 supplies power to the primary winding and simultaneously charges the third energy storage capacitor C13. The primary control circuit 21 outputs a second primary drive signal PDRV2 to control the conduction and cutoff of the fifth transistor Q23. For example, when the second primary drive signal PDRV2 output by the primary control circuit 21 is high, it controls the fifth transistor Q23 to conduct, at which time the second input voltage VIN2 supplies power to the second transformer T2. When the second primary drive signal PDRV2 output by the primary control circuit 21 is low, it controls the primary transistor Q35 to turn off, at which time the third energy storage capacitor C13 supplies power to the second transformer T2, thus controlling the conduction or cutoff of the primary winding circuit of the second transformer T2. It can be understood that when the primary control circuit 21 outputs the second primary drive signal PDRV2 to control the fifth transistor Q23 to turn off, the third energy storage capacitor C13, the second resistor R2, the primary winding, and the second diode D2 form a discharge circuit to release the energy stored in the third energy storage capacitor C13.

[0064] Figure 4 For waveform diagrams of some signals during the operation of the switching power supply circuit provided in this application embodiment, please refer to [link / reference]. Figure 4 As shown, Figure 4This diagram illustrates the waveforms of the primary current Ip in the primary winding circuit of the second transformer T2, the secondary current Is in the secondary winding circuit of the second transformer T2, and the second primary drive signal PDRV2 during the energy storage and release phases of the second transformer T2. (Combined with...) Figure 4 It can be seen that during the time period t0-t1, the second transformer T2 is in the energy storage stage, and the primary control circuit 21 outputs the second primary drive signal PDRV2 at a high level. At this time, the fifth transistor Q23 in the primary winding circuit of the second transformer T2 is turned on, and the primary winding circuit of the second transformer T2 is in the charging process. Figure 4 As can be seen, during the time interval t0-t1, the primary current Ip in the primary winding circuit of the second transformer T2 increases linearly, while the secondary current Is in the secondary winding circuit of the second transformer T2 remains at a stable low value. At time t1, the primary control circuit 21 outputs the second primary drive signal PDRV2 at a low level, which turns off the fifth transistor Q23 in the primary winding circuit of the second transformer T2. From time t1 onwards, the second transformer T2 is in the enabling stage, and the primary current Ip in the primary winding circuit of the second transformer T2 decreases to 0. At this time, the secondary current Is in the secondary winding circuit of the second transformer T2 gradually decreases. Specifically, when the second transformer T2 is in the enabling stage, the second transformer T2 first discharges to the first discharge branch Vo1, and then, through the channel switch switching control, the secondary winding of the second transformer T2 discharges to the second discharge branch Vo2.

[0065] In one embodiment of this application, the switching power supply circuit further includes multiple voltage sampling circuits, each voltage sampling circuit being used to sample the discharge voltage on a corresponding discharge branch; the secondary control circuit 23 is also used to acquire multiple discharge voltages on all discharge branches, sort the voltage values ​​of the multiple discharge voltages from low to high, and, during the energy release phase, sequentially control the multiple discharge branches to conduct in order of discharge voltage from low to high to discharge externally.

[0066] It is understandable that, since different electronic devices have different discharge voltages during charging, the discharge voltage of each discharge branch in a power supply circuit with multiple outputs will be different. In this embodiment, a voltage sampling circuit (not shown in the figure) can collect the discharge voltage of each discharge branch, and then sort the discharge voltages from smallest to largest. In one discharge cycle, the secondary circuit and the discharge branch with the smaller discharge voltage are prioritized to discharge the external electronic device. When the discharge time reaches the set time, the secondary winding circuit is switched to discharge the next discharge branch. In this way, because the discharge branches are turned on and discharged in order of smallest discharge voltage, the discharge efficiency is improved. Figure 4The secondary current Is in the secondary winding circuit of the second transformer T2 decreases at a relatively gradual rate to avoid large ripples in the secondary current Is, which could affect the stability of the circuit. Understandably, if within one energy release cycle, the secondary winding is first switched to the discharge branch with the higher discharge voltage, the secondary current Is in the secondary winding circuit of the second transformer T2 will decrease rapidly. Figure 4 The waveform of the secondary current Is in the secondary winding circuit of the second transformer T2 is relatively steep, which can easily cause current ripple in the circuit and thus affect the stability of the circuit.

[0067] In one embodiment of this application, the power supply circuit further includes a voltage comparison circuit composed of multiple comparators. The voltage comparison circuit is used to compare the discharge voltages sampled by multiple voltage sampling circuits to determine the order of magnitude of the multiple discharge voltages.

[0068] It is understood that, in one embodiment of this application, in a power supply circuit with multiple discharge branches, it is not necessary to switch smoothly according to the charging current from small to large. The above is just a preferred discharge channel switching control method provided by the embodiment of this application, and does not limit this application to controlling the switching to different discharge branches only according to the above discharge channel switching method.

[0069] Please continue reading Figure 3 As shown, the switching power supply circuit also includes a comparator COMP. The input of the comparator COMP is used to sample the discharge voltages corresponding to the two discharge branches and compare the voltage values ​​of the discharge voltages to output the comparison result to the secondary control circuit 23. For example, in this embodiment, the voltage sampling circuit samples the first discharge voltage Vo11 on the first discharge branch Vo1 and the second discharge voltage Vo21 on the second discharge branch Vo2, and then compares the first discharge voltage Vo11 and the second discharge voltage Vo21.

[0070] In this embodiment, the second transformer T2 stores energy during the conduction phase of the fifth transistor Q23 on the primary side, and releases energy to each discharge branch in the secondary winding circuit during the energy release phase. During the energy release phase, through the action of the output comparator circuit, the system will first open the path with the lower discharge voltage. In this embodiment, taking the first discharge voltage Vo11 being less than the second discharge voltage Vo21 as an example, the working principle of the dual-channel switching power supply circuit provided in this application embodiment is explained as follows:

[0071] Figure 5 For waveform diagrams of the control signals during operation of the dual-output switching power supply circuit provided in this application embodiment, please refer to [link / reference]. Figure 5As shown, in this embodiment, the control of multiple transistors on the two secondary output paths is changed from one control signal controlling a pair of back-to-back transistors to two signals controlling a pair of transistors respectively, that is, one control signal controls one transistor respectively.

[0072] Figure 6 One of the schematic diagrams showing the current flow direction during operation of the dual-output switching power supply circuit provided in the embodiments of this application; Figure 7 This is the second schematic diagram showing the current flow direction during operation of the dual-output switching power supply circuit provided in this application embodiment. Figure 8 This is the third schematic diagram showing the current flow direction during operation of the dual-output switching power supply circuit provided in this application embodiment. Figure 9 This is the fourth schematic diagram showing the current flow direction during operation of the dual-output switching power supply circuit provided in this application embodiment. Figure 10 The fifth schematic diagram of the current flow direction during operation of the dual-output switching power supply circuit provided in the embodiments of this application.

[0073] Please see Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 as well as Figure 10 As shown, during operation, when the fifth transistor Q23 in the primary circuit is turned off, the secondary control circuit will prioritize turning on the discharge branch with the lower discharge voltage. This means that the transistors on the discharge branch with the lower discharge voltage need to be turned on first. In this embodiment, the first discharge voltage Vo11 on the first discharge branch Vo1 is lower, while the second discharge voltage Vo21 on the second discharge branch Vo2 is higher. At the very beginning of the energy release phase, i.e. Figure 5 During the time interval t0-t1, the first control signal S11 and the second control signal S12 output by the secondary control circuit 23 are high, while the third control signal S21 and the fourth control signal S22 are low. During this time period, the secondary energy of the second transformer T2 is first supplied to the first discharge branch Vo1. Please refer to the relevant documentation for details. Figure 6 As shown, at this time, the current on the first discharge branch Vo1 is output to the outside through the first transistor Q11 and the second transistor Q22.

[0074] During the brief period when the first transistor Q11 is off, the second transistor Q12 is on, but the fourth transistor Q22 is temporarily off, the current flow in the secondary circuit is as follows: Figure 7 As shown, please refer to Figure 7As shown, at this time, the second DC current Vo-Pre2 output by the secondary winding is connected to the first discharge branch Vo1 by the parasitic diode of the first transistor Q11 and the second transistor Q12. The secondary energy is still only transferred to the first discharge branch Vo1, and there is no risk of secondary energy accumulation in the circuit system.

[0075] The secondary control circuit 23 will control the opening time of the two discharge branches Vo1 and Vo2 according to their load conditions. This is done using an existing method, which will not be elaborated further. When the opening time of the first discharge branch Vo1 is about to end, i.e. Figure 5 At time t1, the first control signal S11 first changes from high level to low level, and the first transistor Q11 is turned off. Please refer to the corresponding information at this time. Figure 8 As shown, at this time, the second DC current Vo-Pre2 output by the secondary winding is connected to the first discharge branch Vo1 by the parasitic diode of the first transistor Q11 and the second transistor Q12. The secondary energy is still only transferred to the first discharge branch Vo1, and there is no risk of secondary energy accumulation in the circuit system.

[0076] Then, before turning off the second transistor Q12, the fourth transistor Q22 is turned on first, that is, before... Figure 5 The fourth control signal S22 is preferentially switched from low to high to control the fourth transistor Q22 to conduct. At this time, since the first discharge voltage Vo11 output on the first discharge branch Vo1 is relatively low, secondary energy is still only transferred to the first discharge branch Vo1, and the circuit system is still safe. Then, after the fourth control signal S22 is switched from low to high, the second control signal S12 is changed from high to low. At this time, the channel for secondary energy to freewheel from the first discharge branch Vo1 is closed. After the second DC voltage Vo-Pre2 rises to the voltage Vo12+Vdiode, the secondary energy can directly flow from the parasitic diode of the third transistor Q21 and the conduction of the fourth transistor Q22 to the second discharge branch Vo2, and there will be no situation where energy has nowhere to be released. Please refer to the corresponding section at this time. Figure 9 As shown, at this time, the secondary energy can be directly freewheeled from the parasitic body diode of the third transistor Q21 and the fourth transistor Q22 to the second discharge branch Vo2.

[0077] Finally, at time t2, the third control signal S21 changes from low to high again. At this time, the third transistor Q21 and the fourth transistor Q22 on the second discharge branch Vo2 are fully turned on. Please refer to the corresponding information at this time. Figure 10As shown, at this point, secondary energy can directly flow from the third transistor Q21 and the fourth transistor Q22 to the second discharge branch Vo2; the power supply system has completed the switching process from the first discharge branch Vo1 to the second discharge branch Vo2. Moreover, during the entire switching process, there is no risk of direct connection between the first discharge branch Vo1 and the second discharge branch Vo2, nor is there a situation where secondary energy has nowhere to flow, ensuring the reliability of the power supply system and avoiding the technical problem of voltage spikes damaging the power circuit system; it also avoids the technical problem of designing a dedicated energy absorption circuit, increasing hardware costs and circuit complexity. Similarly, the control method is similar during the switching process from the second discharge branch Vo2 to the first discharge branch Vo1.

[0078] Please see Figure 6 As shown, in one embodiment of this application, the switching power supply circuit further includes a sixth transistor Q6. The sixth transistor Q6 is a PMOS transistor with its source grounded and its drain connected to the same terminal of the secondary winding. The gate of the sixth transistor Q6 can receive a sixth control signal SRG output by the secondary control circuit 23. The sixth control signal SRG is used to control the conduction or turn-off of the sixth transistor Q6, thereby controlling the conduction or turn-off of the secondary circuit.

[0079] In one embodiment of this application, please continue to refer to Figure 3 The switching power supply circuit also includes an isolation circuit 22, through which the primary control circuit 21 is connected to the secondary control circuit 23. It is understood that in the isolated switching power supply circuit, the isolation circuit 22 mainly serves to ensure safety, stability, and noise isolation, thereby guaranteeing the stable operation of the switching power supply; further details will not be elaborated here.

[0080] Figure 11 This is a flowchart of a control method for a switching power supply circuit provided in an embodiment of this application. The switching power supply circuit of this embodiment includes a transformer, a primary control circuit, a secondary control circuit, and at least two discharge branches. The primary control circuit is disposed in the primary winding circuit of the transformer to control the primary winding to store and release energy. The input terminal of the discharge branch is connected to the output terminal of the secondary winding circuit of the transformer, and the output terminal of the discharge branch is used to output a discharge voltage. Each discharge branch has two transistors disposed back to back, and the control electrode of each transistor is connected to the secondary control circuit. The secondary control circuit is used to control the operation of the transistors in the discharge branch to control the output state switching of the discharge branch.

[0081] Among them, with Figure 3Taking the dual-output switching power supply circuit shown as an example, the switching power supply circuit includes: a second transformer T2, a primary control circuit 21, a secondary control circuit 23, and two discharge branches. The primary control circuit 21 is located in the primary winding circuit of the second transformer T2 to control the primary winding to store and release energy. The input terminal of the discharge branch is connected to the output terminal of the secondary winding circuit of the second transformer T2, and the output terminal of the discharge branch is used to output the discharge voltage. The secondary control circuit 23 is used to control the conduction and cutoff of each discharge branch, thereby controlling the output state switching between the secondary winding and each discharge branch. Among them, the two discharge branches are the first discharge branch Vo1 and the second discharge branch Vo2. The first discharge branch Vo1 includes a first transistor Q11 and a second transistor Q12 arranged back to back, and the second discharge branch Vo2 includes a third transistor Q21 and a fourth transistor Q22 arranged back to back. The two discharge branches are the first discharge branch Vo1 and the second discharge branch Vo2. The first discharge branch Vo1 includes a first transistor Q11 and a second transistor Q12 arranged back to back, and the second discharge branch Vo2 includes a third transistor Q21 and a fourth transistor Q22 arranged back to back.

[0082] The control method provided in this embodiment is mainly used in the secondary control circuit 23. During one energy release cycle, when the output state of the first discharge branch Vo1 and the second discharge branch Vo2 switches, the control method includes:

[0083] S101, control the first transistor on the first discharge branch to turn off and the second transistor to turn on, so that the first discharge branch discharges to the outside through the body diode of the first transistor.

[0084] S102. Before the second transistor is turned off, the fourth transistor is turned on so that the second discharge branch discharges to the outside through the body diode of the third transistor and the fourth transistor.

[0085] S103. After the fourth transistor is turned on, the second transistor is turned off and the third transistor is turned on in sequence, so that the second discharge branch discharges to the outside through the third transistor and the fourth transistor.

[0086] According to the control method provided in this embodiment, during the switching process of the two discharge branches, one discharge branch is always in a conducting state to absorb the excess energy output by the secondary winding, thus avoiding the technical problem of generating voltage spikes and damaging the power supply circuit system.

[0087] In one embodiment of this application, the control method further includes: acquiring multiple discharge voltages on all discharge branches, sorting the voltage values ​​of the multiple discharge voltages from low to high, and controlling the multiple discharge branches to conduct in sequence to discharge to the outside according to the order of discharge voltage from low to high during the energy release phase.

[0088] Because different electronic devices have different discharge voltages during charging, the discharge voltage of each discharge branch in a power supply circuit with multiple outputs is different. In this embodiment, during one discharge cycle, the secondary circuit and the discharge branch with the lower discharge voltage are prioritized to discharge the external electronic device. Once the discharge time reaches the set value, the secondary winding circuit is switched to discharge the next discharge branch. This sequentially discharges the branches according to their discharge voltage, resulting in a relatively gradual decrease in the secondary current Is in the secondary winding circuit of the second transformer T2. This avoids large ripples in the secondary current Is, which could affect circuit stability. It is understandable that if, during one discharge cycle, the secondary winding is switched to the discharge branch with the higher discharge voltage first, the secondary current Is in the secondary winding circuit of the second transformer T2 would decrease rapidly, resulting in a steep waveform. This could easily cause current ripples in the circuit, affecting its stability.

[0089] This application also provides a chip, which can be a power supply chip, and the chip includes a switching power supply circuit as provided in one of the above embodiments.

[0090] This application also provides an electronic device, which can be a power adapter or other electronic device with external charging function. The electronic device includes a switching power supply as provided in any of the above embodiments; or the electronic device includes a chip as provided in the above embodiments.

[0091] Finally, it should be noted that the above embodiments are merely specific implementations of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A switching power supply circuit, characterized in that, include: Transformer, primary control circuit, secondary control circuit, and at least two discharge branches; The primary control circuit is installed in the primary winding circuit of the transformer to control the primary winding to store and release energy; the input terminal of the discharge branch is connected to the output terminal of the secondary winding circuit of the transformer, and the output terminal of the discharge branch is used to output the discharge voltage. The secondary control circuit is used to control the conduction and cutoff of each discharge branch, thereby controlling the output state switching between the secondary winding and each discharge branch. Specifically, for any first discharge branch and second discharge branch among the at least two discharge branches, the first discharge branch includes a first transistor and a second transistor arranged back to back, and the second discharge branch includes a third transistor and a fourth transistor arranged back to back; the control electrodes of the first transistor, the second transistor, the third transistor, and the fourth transistor are all connected to the secondary control circuit. Specifically, when controlling the output state switching of the first discharge branch and the second discharge branch, the secondary control circuit is used to: firstly, control the first transistor on the first discharge branch to turn off and the second transistor to turn on, so that the first discharge branch discharges to the outside through the body diode of the first transistor; then, before the second transistor turns off, control the fourth transistor to turn on, so that the second discharge branch discharges to the outside through the body diode of the third transistor and the fourth transistor; finally, control the second transistor to turn off and control the third transistor to turn on in sequence, so that the second discharge branch discharges to the outside through the third transistor and the fourth transistor.

2. The switching power supply circuit according to claim 1, characterized in that, The switching power supply circuit also includes multiple voltage sampling circuits, each of which is used to sample the discharge voltage of a corresponding discharge branch. The secondary control circuit is also used to acquire multiple discharge voltages on all discharge branches, sort the voltage values ​​of the multiple discharge voltages from low to high, and, during the energy release phase, sequentially control the multiple discharge branches to conduct in order of the discharge voltages from low to high to discharge to the outside.

3. The switching power supply circuit according to claim 2, characterized in that, The switching power supply circuit further includes at least one comparator, which is used to sample the discharge voltages corresponding to any two discharge branches and compare the voltage values ​​of the discharge voltages to output the comparison result to the secondary control circuit.

4. The switching power supply circuit according to any one of claims 1-3, characterized in that, The discharge branch also includes an energy storage capacitor, the first end of which is connected to the high-voltage end of the discharge branch, and the second end of which is grounded.

5. The switching power supply circuit according to any one of claims 1-3, characterized in that, The switching power supply circuit also includes an isolation circuit, through which the primary control circuit is connected to the secondary control circuit.

6. The switching power supply circuit according to any one of claims 1-3, characterized in that, The switching power supply circuit also includes a rectifier circuit, the input terminal of which is connected to the output terminal of the secondary winding of the transformer, and the output terminal of which is connected to the input terminal of the discharge branch. The rectifier circuit is used to rectify the AC power output from the secondary winding and output the corresponding DC power.

7. A control method for a switching power supply circuit, characterized in that, The switching power supply circuit includes a transformer, a primary control circuit, a secondary control circuit, and at least two discharge branches. The primary control circuit is located in the primary winding circuit of the transformer to control the primary winding to store and release energy. The input terminal of the discharge branch is connected to the output terminal of the secondary winding circuit of the transformer, and the output terminal of the discharge branch is used to output the discharge voltage. The secondary control circuit is used to control the conduction and cutoff of each discharge branch, thereby controlling the output state switching between the secondary winding and each discharge branch. Specifically, for any first discharge branch and second discharge branch among the at least two discharge branches, the first discharge branch includes a first transistor and a second transistor arranged back to back, and the second discharge branch includes a third transistor and a fourth transistor arranged back to back. During an energy release cycle, when the output state of the first discharge branch and the second discharge branch switches, the control method includes: The first transistor in the first discharge branch is turned off and the second transistor is turned on, so that the first discharge branch discharges to the outside through the body diode of the first transistor; Before the second transistor is turned off, the fourth transistor is controlled to be turned on, so that the second discharge branch discharges to the outside through the body diode of the third transistor and the fourth transistor; After the fourth transistor is turned on, the second transistor is turned off and the third transistor is turned on in sequence, so that the second discharge branch discharges to the outside through the third transistor and the fourth transistor.

8. The control method for a switching power supply circuit according to claim 7, characterized in that, The control method further includes: acquiring multiple discharge voltages on all discharge branches, sorting the voltage values ​​of the multiple discharge voltages from low to high, and controlling the multiple discharge branches to conduct in sequence to discharge to the outside according to the order of the discharge voltages from low to high during the energy release phase.

9. A chip, characterized in that, Includes the switching power supply circuit as described in any one of claims 1-6.

10. An electronic device, characterized in that, It includes the switching power supply as described in any one of claims 1-6; or it includes the chip as described in claim 9.

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