FCCM mode output discharge control method, control device and switching power supply

Abstract

The invention provides an FCCM mode output discharge control method, a control device and a switching power supply, which are applied to light no-load shutdown of the switching power supply, and the FCCM mode output discharge control method comprises the following steps: a power-down shutdown type identification step: identifying whether the power-down shutdown type is input voltage non-open-circuit type power-down shutdown or input voltage open-circuit type power-down shutdown; a shutdown control strategy execution step: executing a corresponding control strategy according to the power-down shutdown type, detecting a negative current peak value in real time when the output flows backward to the input in the shutdown process, and limiting the negative current peak value within a negative current threshold value, during shutdown, when the power-down shutdown type is input voltage non-open-circuit power-down shutdown, the output voltage is made to flow back to the input side to be recycled; when the power-down shutdown type is input voltage open circuit type power-down shutdown, the output voltage is consumed. The invention can ensure that the output voltage rises monotonically when the switching power supply is restarted, and can reduce the cost and volume of the switching power supply.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converters, and in particular to an FCCM mode output discharge control method. Background Art

[0002] With the development of science and technology, switching power supplies have become an inseparable part of various industries. Their importance is self-evident. As a result, the performance requirements for switching power supplies are becoming increasingly stringent. In some industries, especially the communication power supply industry, for example, the switching power supply is used to power the power amplifier. The power supply quality directly affects the quality of the radio signal. Therefore, the monotonicity of the output voltage rise during the startup process of the switching power supply is required to be higher.

[0003] Usually, the switching power supply will use the discontinuous conduction mode (hereinafter referred to as DCM mode) and the forced continuous conduction mode (hereinafter referred to as FCCM mode) under light no-load. Because the inductor current is in a discontinuous state in the DCM mode, the dynamic response speed is slow. In applications where the dynamic response speed of the switching power supply is required to be high, such as the communication power supply industry, it cannot meet the actual application. In this application scenario, the FCCM mode is usually used. When the load jumps dynamically, it can respond in time to avoid the output voltage overshoot or undershoot beyond the range, which affects the normal operation of the subsequent system.

[0004] Under light no-load conditions, when the switching power supply adopts FCCM mode, when the output voltage is higher than the input voltage, the output voltage can be fed back to the input side by reverse flow, especially when the output has a large-capacity capacitor. If the switching power supply stops working directly after shutdown, the output voltage cannot be fed back to the input side, and the output will have a very high voltage residue, which will exist for a long time and basically cannot be consumed. Figure 1 As shown, when the machine is restarted, the output will flow back to the input side, causing the output voltage to drop rapidly. The output voltage will not rise until the input energy is greater than the output energy. This does not meet the startup monotonicity and affects the normal operation of the subsequent system.

[0005] In addition, the input and output ends of the switching power supply are usually equipped with large-capacity capacitors. When the FCCM mode is used, under light no-load conditions, when the input voltage circuit is disconnected by a circuit breaker, for example, after the input voltage circuit is disconnected by an air switch, the output voltage flows back to the input. Because there is no circuit discharge, it is finally stored in the input capacitor. Figure 2 As shown, when the switching power supply is just shut down due to undervoltage, it rises rapidly again and exceeds the voltage shutdown threshold, causing the switching power supply to restart again, which will affect the reliability of the switching power supply shutdown. Under some working conditions, such as lightning strikes, static electricity, input power failure, etc., the input voltage drops rapidly, causing the output to flow back to the input, and the negative current in the switching power supply will continue to increase. If the negative current is not limited, the switching power supply will be damaged.

[0006] In the industry, in order to solve the above problems, an additional discharge circuit is added to the output or input end of the switching power supply to consume the residual voltage, ensure that the output voltage rises monotonically when the power is restarted, and that the power supply system is safe. However, this solution will increase the cost and size of the power supply system. Summary of the invention

[0007] In view of this, the technical problem to be solved by the present invention is to provide an FCCM mode output discharge control method, a control device and a switching power supply, which do not require an additional discharge circuit. When the power is turned off, the output voltage is fed back to the input side for recovery or consumption, so that the output discharge is completed, ensuring that the output voltage rises monotonically when the power is restarted, and avoiding the shutdown and restart problem.

[0008] As a first aspect of the present invention, an embodiment of a method for controlling FCCM mode output discharge is provided as follows:

[0009] A FCCM mode output discharge control method is applied to the light no-load shutdown of a switching power supply, wherein the switching power supply includes a main switch tube and a synchronous freewheeling tube, wherein the FCCM mode output discharge control method includes the following steps:

[0010] A power-off shutdown type identification step, identifying whether the power-off shutdown type is an input voltage non-circuit-breaking type power-off shutdown or an input voltage circuit-breaking type power-off shutdown;

[0011] The shutdown control strategy execution step executes the corresponding control strategy according to the power-off shutdown type. At the same time, during the shutdown process, the negative current peak value when the output flows back to the input is detected in real time, and the negative current peak value is limited within the negative current threshold:

[0012] When the power-off shutdown type is the input voltage non-circuit-breaking power-off shutdown, the control strategy is: at the moment of the switch power supply shutdown, all the switch tubes in the switch power supply continue to work, while reducing the duty cycle of the main switch tube and increasing the duty cycle of the synchronous freewheeling tube, and the output voltage flows back to the input side and finally feeds back to the input power supply. After the first time period, all the switch tubes in the switch power supply are turned off to complete the shutdown;

[0013] When the power-off shutdown type is the input voltage circuit-breaking power-off shutdown, the control strategy is: when the input voltage drops to the undervoltage shutdown threshold, the switch tube connected to the positive end of the input voltage is turned off first, and the remaining switch tubes continue to work. At the same time, the duty cycle of the synchronous freewheeling tube is increased, and the output voltage flows back to the input side, causing the input voltage to rise. Until the input voltage drops to the undervoltage shutdown threshold again, all the switch tubes in the switching power supply are turned off to complete the shutdown.

[0014] Furthermore, when the input voltage first drops to the undervoltage shutdown threshold, and then within the set time, the input voltage is higher than the first threshold, the power-off shutdown type is identified as input voltage circuit-breaking power-off shutdown, otherwise it is input voltage non-circuit-breaking power-off shutdown.

[0015] Furthermore, the first threshold is greater than the under-voltage shutdown threshold.

[0016] Furthermore, the input voltage non-circuit-breaking type power-off shutdown includes input power shutdown and Ctrl shutdown; the input voltage circuit-breaking type power-off shutdown includes a shutdown in which an air switch or a circuit breaker disconnects the power supply circuit.

[0017] Furthermore, when the input voltage non-circuit-breaking type power-off shutdown is an input power shutdown, the first duration timing starts when the input voltage first drops to the undervoltage shutdown threshold; when the input voltage non-circuit-breaking type power-off shutdown is a Ctrl shutdown, the first duration timing starts when the Ctrl shutdown reaches the shutdown threshold.

[0018] Furthermore, the switching power supply further comprises a synchronous rectifier tube, wherein: when the absolute value of the negative current peak sampling value is greater than the absolute value of the negative current threshold value, the synchronous rectifier tube is turned off cycle by cycle.

[0019] Furthermore, the absolute value of the negative current threshold is greater than zero and less than or equal to the maximum forward current that the switching power supply can withstand.

[0020] As a second aspect of the present invention, the technical solution of the embodiment of the FCCM mode output discharge control device is as follows:

[0021] An FCCM mode output discharge control device is applied to the light no-load shutdown of a switching power supply, wherein the switching power supply includes a main switch tube and a synchronous freewheeling tube, wherein the FCCM mode output discharge control device includes the following units:

[0022] A power-off shutdown type identification unit, used to identify whether the power-off shutdown type is an input voltage non-circuit-breaking type power-off shutdown or an input voltage circuit-breaking type power-off shutdown;

[0023] The shutdown control strategy execution unit is used to execute the corresponding control strategy according to the power-off shutdown type. At the same time, during the shutdown process, the negative current peak value when the output flows back to the input is detected in real time, and the negative current peak value is limited within the negative current threshold:

[0024] When the power-off shutdown type is the input voltage non-circuit-breaking power-off shutdown, the control strategy is: at the moment of the switch power supply shutdown, all the switch tubes in the switch power supply continue to work, while reducing the duty cycle of the main switch tube and increasing the duty cycle of the synchronous freewheeling tube, and the output voltage flows back to the input side and finally feeds back to the input power supply. After the first time period, all the switch tubes in the switch power supply are turned off to complete the shutdown;

[0025] When the power-off shutdown type is the input voltage circuit-breaking power-off shutdown, the control strategy is: when the input voltage drops to the undervoltage shutdown threshold, the switch tube connected to the positive end of the input voltage is turned off first, and the remaining switch tubes continue to work. At the same time, the duty cycle of the synchronous freewheeling tube is increased, and the output voltage flows back to the input side, causing the input voltage to rise. Until the input voltage drops to the undervoltage shutdown threshold again, all the switch tubes in the switching power supply are turned off to complete the shutdown.

[0026] As a third aspect of the present invention, the technical solution of the embodiment of the switching power supply provided is as follows:

[0027] A switching power supply, comprising the FCCM mode output discharge control device as described in any one of the second aspects above.

[0028] Furthermore, the adopted topology is a buck single-stage topology, or a cascade topology including a buck and an isolation switch power supply circuit; or a cascade topology including a buck-boost and an isolation switch power supply circuit.

[0029] Furthermore, the isolation switch power supply circuit is a bridge circuit, or a push-pull circuit, or an LLC circuit.

[0030] Furthermore, the main switch tube is electrically magnetized when it is turned on.

[0031] Terminology explanation:

[0032] Input power shutdown: The power supply that provides input to the switching power supply is shut down.

[0033] Ctrl shutdown: Ctrl is the remote control terminal of the switching power supply. When Ctrl is shut down, it normally provides input for the switching power supply, but the switching power supply has no output voltage.

[0034] Compared with the existing FCCM control scheme, the present invention has the following beneficial effects:

[0035] (1) The FCCM mode output discharge control method provided by the embodiment of the present invention, when the switching power supply is shut down, the output voltage flows back to the input side and is finally fed back to the input power supply or consumed, thereby ensuring that the output voltage rises monotonically when the power supply is restarted;

[0036] (2) In the FCCM mode output discharge control method provided by the embodiment of the present invention, when the input voltage is disconnected and the switching power supply is shut down, for example, when the air switch is shut down, when the input voltage drops to the undervoltage threshold, the switch tube associated with the positive end of the input voltage is shut down first, and the remaining switch tubes continue to work, and the output voltage flows back to the input side. Since the power supply driven by the switch tube comes from the input, the switch tube continues to work and can quickly consume the voltage at the input end, thereby avoiding the problem of restarting the machine due to the rapid rise of the input voltage caused by the output backflow, thereby ensuring the monotonicity of the shutdown;

[0037] (3) The FCCM mode output discharge control method provided by the embodiment of the present invention has simple control logic and can reduce the cost and volume of the switching power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a waveform diagram of the output voltage backflow when the switching power supply in the prior art is restarted after being shut down without load;

[0039] Figure 2 A schematic diagram of a waveform of a prior art switching power supply in which the output voltage flows back to the input after the input power supply is disconnected and shut down, and the input voltage rises;

[0040] Figure 3 It is a flow chart of the FCCM mode output discharge control method according to the first embodiment of the present invention;

[0041] Figure 4 It is a principle block diagram of the FCCM mode output discharge control device according to the second embodiment of the present invention;

[0042] Figure 5 A specific circuit diagram of a switching power supply according to a third embodiment of the present invention;

[0043] Figure 6 for Figure 5 A specific flow chart of the output discharge control method of the switching power supply FCCM mode;

[0044] Figure 7 for Figure 5 Schematic diagram of input voltage when the switching power supply is turned off;

[0045] Figure 8 for Figure 5 Schematic diagram of the output voltage when the switching power supply is turned on. DETAILED DESCRIPTION

[0046] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0047] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0048] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application are described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, the process, method, system, product or equipment comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0049] It should be understood that, in the specification, claims and drawings, when a step is described as being connected to another step, the step may be directly connected to the other step, or be connected to the other step through a third step; when an element / unit is described as being "connected" to another element / unit, the element / unit may be "directly connected" to the other element / unit, or be "connected" to the other element / unit through a third element / unit.

[0050] In addition, the drawings of the present disclosure are only schematic diagrams of the present disclosure and are not necessarily drawn to scale. The same symbols in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented using software, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontrollers.

[0051] First embodiment

[0052] This embodiment provides an FCCM mode output discharge control method, which is applied to the light no-load shutdown of a switching power supply, wherein the switching power supply includes a main switch tube and a synchronous freewheeling tube. Figure 3 This is a flow chart of the FCCM mode output discharge control method of the first embodiment of the present invention. Figure 3 , which includes the following steps:

[0053] A power-off shutdown type identification step S100, identifying whether the power-off shutdown type is an input voltage non-circuit-breaking type power-off shutdown or an input voltage circuit-breaking type power-off shutdown;

[0054] The shutdown control strategy executes step S200, and executes the corresponding control strategy according to the power-off shutdown type. At the same time, during the shutdown process, the negative current peak value when the output flows back to the input is detected in real time, and the negative current peak value is limited within the negative current threshold. This step is divided into two working conditions as follows:

[0055] In step S201 of the first working condition, when the power-off shutdown type is the input voltage non-circuit-breaking power-off shutdown, the control strategy is: at the moment of the switch power supply shutdown, all the switch tubes in the switch power supply continue to work, and at the same time, the duty cycle of the main switch tube is reduced, and the duty cycle of the synchronous freewheeling tube is increased, and the output voltage is reversed to the input side, and finally fed back to the input power supply, and after the first time period, all the switch tubes in the switch power supply are turned off to complete the shutdown;

[0056] In step S202 under the second working condition, when the power-off shutdown type is the input voltage circuit-breaking power-off shutdown, the control strategy is: when the input voltage drops to the undervoltage shutdown threshold, the switch tube connected to the positive end of the input voltage is turned off first, and the remaining switch tubes continue to work. At the same time, the duty cycle of the synchronous freewheeling tube is increased, and the output voltage flows back to the input side, causing the input voltage to rise, until the input voltage drops to the undervoltage shutdown threshold again, all the switch tubes in the switching power supply are turned off to complete the shutdown.

[0057] In the second working condition, when the remaining switch tubes continue to work, the power supply for the switch tube driver comes from the input voltage. Since the remaining switch tubes continue to work, the voltage at the input end can be quickly consumed.

[0058] When shutting down, this embodiment allows the output voltage to flow back to the input side for recovery or consumption, so that the output is discharged, ensuring that the output voltage rises monotonically when restarting, and avoiding the shutdown and restart problem. During the shutdown process, the system will detect the negative current when the output flows back to the input, limit it within a certain range, and ensure that the system will not be damaged. The control logic of the present invention is simple, and no additional discharge circuit is required, which can reduce the cost and volume of the power supply system.

[0059] As a specific implementation method, when the input voltage first drops to the undervoltage shutdown threshold, and then within the set time, the input voltage is higher than the first threshold, the power-off shutdown type is identified as an input voltage circuit-breaking type power-off shutdown, otherwise it is an input voltage non-circuit-breaking type power-off shutdown.

[0060] Further, the first threshold is greater than the under-voltage shutdown threshold.

[0061] As a specific implementation method, when the input voltage non-circuit-breaking type power-off shutdown is an input power shutdown, the first duration timing starts when the input voltage first drops to the undervoltage shutdown threshold; when the input voltage non-circuit-breaking type power-off shutdown is a Ctrl shutdown, the first duration timing starts when the Ctrl shutdown reaches the shutdown threshold.

[0062] As a specific implementation, the switching power supply also includes a synchronous rectifier. When the absolute value of the negative current peak sampling value is greater than the absolute value of the negative current threshold, the synchronous rectifier is turned off cycle by cycle. The purpose is to prevent the output voltage from flowing back and the negative current from continuing to increase, thereby controlling the negative current within a certain range and ensuring that the switching power supply will not be damaged.

[0063] As a specific implementation, the absolute value of the negative current threshold is greater than zero and less than or equal to the maximum forward current that the switching power supply can withstand.

[0064] Second embodiment

[0065] This embodiment provides an FCCM mode output discharge control device, which is applied to the light no-load shutdown of a switching power supply. The switching power supply includes a main switch tube and a synchronous freewheeling tube. Figure 4 This is a functional block diagram of the FCCM mode output discharge control device of the second embodiment of the present invention. Figure 4 , which includes the following units:

[0066] A power-off shutdown type identification unit 100, used to identify whether the power-off shutdown type is an input voltage non-disconnection type power-off shutdown or an input voltage disconnection type power-off shutdown;

[0067] The shutdown control strategy execution unit 200 is used to execute the corresponding control strategy according to the power-off shutdown type. At the same time, during the shutdown process, the negative current peak value when the output flows back to the input is detected in real time, and the negative current peak value is limited within the negative current threshold:

[0068] When the power-off shutdown type is the input voltage non-circuit-breaking power-off shutdown, the control strategy is: at the moment of the switch power supply shutdown, all the switch tubes in the switch power supply continue to work, while reducing the duty cycle of the main switch tube and increasing the duty cycle of the synchronous freewheeling tube, and the output voltage flows back to the input side and finally feeds back to the input power supply. After the first time period, all the switch tubes in the switch power supply are turned off to complete the shutdown;

[0069] When the power-off shutdown type is the input voltage circuit-breaking power-off shutdown, the control strategy is: when the input voltage drops to the undervoltage shutdown threshold, the switch tube connected to the positive end of the input voltage is turned off first, and the remaining switch tubes continue to work. At the same time, the duty cycle of the synchronous freewheeling tube is increased, and the output voltage flows back to the input side, causing the input voltage to rise. Until the input voltage drops to the undervoltage shutdown threshold again, all the switch tubes in the switching power supply are turned off to complete the shutdown.

[0070] The technical means adopted by the control device of this embodiment correspond to and are consistent with the control method of the first embodiment, and have the same beneficial effects, so they will not be described in detail.

[0071] In addition, the preferred technical means or further improved means of each step in the control method of the first embodiment can be extended to the corresponding units of this embodiment, and this embodiment will not describe them one by one.

[0072] Third embodiment

[0073] This embodiment provides a switching power supply, which includes the FCCM mode output discharge control device described in any one of the second embodiments.

[0074] Since the switching power supply of this embodiment includes the FCCM mode output discharge control device described in any one of the second embodiments, it can ensure that the output voltage rises monotonically when the switching power supply is restarted, and can reduce the cost and volume of the switching power supply.

[0075] Furthermore, the topology adopted by the switching power supply of this embodiment is a buck single-stage topology, or a cascade topology including a buck and an isolation switching power supply circuit; or a cascade topology including a buck-boost and an isolation switching power supply circuit.

[0076] Furthermore, the isolating switch power supply circuit is a bridge circuit, or a push-pull circuit, or an LLC circuit.

[0077] Furthermore, when the main switch tube is turned on, the inductor is magnetized.

[0078] Figure 5 A specific circuit diagram of the switching power supply of the third embodiment of the present invention is shown in FIG. Figure 5 , where the switching power supply is a BUCK+ full-bridge topology cascade structure, and the control method used for FCCM mode output discharge is shown in Figure 6 , Figure 5 The main switch tube is the switch tube Q1 in the BUCK circuit, the synchronous freewheeling tube is the switch tube Q2 in the BUCK circuit, and the synchronous rectifier tube is the secondary switch tube Q7 to Q10 in the full-bridge circuit. Figure 5It also includes the BUCK inductor L1, the input capacitor Cin, the output capacitor Cout, the isolation transformer T in the full-bridge circuit and the primary full-bridge switch tubes Q3 to Q6; when the main switch tube Q1 is turned on, the inductor L1 is excited, and when the synchronous freewheeling tube Q2 is turned on, the inductor L1 is demagnetized. When the demagnetization is completed, the inductor current is a negative peak. Figure 6 The control method includes two types of working conditions: input voltage non-circuit-breaking type power-off shutdown and input voltage circuit-breaking type power-off shutdown. Specifically:

[0079] When the input voltage is not a circuit-breaking type power-off shutdown, at the moment of the switch power shutdown, all the switch tubes Q1-Q10 continue to work, and at the same time gradually reduce the duty cycle of the main switch tube Q1. Since the synchronous freewheeling tube Q2 and the main switch tube Q1 are complementary, the duty cycle of the synchronous freewheeling tube Q2 will also increase synchronously. At this time, if the input power is used to shut down, because the input voltage is reduced, the output voltage is higher than the input voltage. At this time, the current in the circuit begins to increase negatively, flows through the secondary rectifier tube and then through the primary full-bridge tube, and finally returns to the input Vin terminal through the main switch tube Q1. There is a power supply on the input side, and the energy that flows back to the primary side is finally fed back to the input power supply. After a timing of 1ms, the output is fully discharged, and then the switch tubes Q1-Q10 are turned off to complete the shutdown. When the machine is restarted, the output voltage waveform is as follows Figure 8 As shown, the output has no electricity and will not flow back, ensuring that the output voltage rises monotonically; if Ctrl is used to shut down, the input voltage always exists at this time. As the duty cycle of the synchronous freewheeling tube Q2 gradually increases, the demagnetization time gradually increases, and the negative current gradually increases. The negative current flows through the secondary rectifier tube and then through the primary full-bridge tube, and finally returns to the input Gnd terminal through the synchronous freewheeling tube Q2. After 1ms of timing, the output is fully discharged, and then the switch tubes Q1-Q10 are turned off to complete the shutdown. When restarting, the output voltage waveform is also as follows Figure 8 As shown, there is no power at the output and no backflow, ensuring that the output voltage rises monotonically;

[0080] When the input voltage is disconnected and the power is turned off, for example, the positive output of the power supply is connected in series with a circuit breaker, and the output of the circuit breaker is connected to the Vin terminal of the switching power supply. When the power is turned off, the circuit breaker is disconnected. When the input voltage drops to the undervoltage shutdown threshold, Q1 is turned off first, and Q2-Q10 continue to work. At the same time, the duty cycle of Q2 is gradually increased. Because the input voltage is reduced, the output voltage is higher than the input voltage. At this time, the current in the loop begins to increase negatively, flows through the secondary rectifier tube and then through the primary full-bridge tube, and finally charges the input capacitor Cin through the body diode of Q1. The input voltage begins to rise, and the input voltage waveform is as follows: Figure 5As shown in the figure, since the power supply driven by the switch tubes Q2-Q10 comes from the input, the switch tubes Q2-Q10 continue to work and can quickly consume the voltage at the input end until the input voltage drops to the undervoltage shutdown threshold again, and then the switch tubes Q2-Q10 are turned off to complete the shutdown; this avoids the output backflow causing the input voltage to rise rapidly, resulting in the problem of restarting the machine, ensuring the monotonicity of the shutdown. When the machine is restarted, the output voltage waveform is as follows Figure 7 As shown, there is no power at the output and no backflow, ensuring that the output voltage rises monotonically;

[0081] At the shutdown moment, the purpose of reducing the duty cycle of the main switch tube Q1 or turning off the main switch tube Q1 is to reduce the energy transferred from the input to the output; the purpose of increasing the duty cycle of the synchronous freewheeling tube Q2 is to allow the inductor L1, Q2 and Q1 to form a reverse Boost circuit to speed up the backflow from the output to the input.

[0082] In the above two shutdown processes, the negative peak current when the output flows back to the input is detected and the negative peak current is limited within a certain range to ensure that the switching power supply will not be damaged;

[0083] When the input voltage first drops to the undervoltage shutdown threshold, and then within 200us, the input voltage is higher than the first threshold, it is identified as an input voltage disconnection type power-off shutdown, otherwise it is an input voltage non-disconnection type power-off shutdown;

[0084] By detecting the negative peak current in the switching power supply circuit when the output flows back to the input cycle by cycle, when the absolute value of the negative current sampling value is greater than the absolute value of the negative current threshold, the synchronous rectifier tubes Q7 to Q10 are turned off cycle by cycle, so that the output voltage cannot flow back and the negative current will not continue to increase. When the absolute value of the negative current sampling value is less than the absolute value of the negative current threshold, the synchronous rectifier tubes Q7 to Q10 work normally, so that the negative current can be controlled within a certain range to ensure that the switching power supply will not be damaged; wherein the absolute value of the negative current threshold is greater than zero and less than or equal to the maximum forward current that the switching power supply can withstand.

[0085] The above are only preferred embodiments of the present invention, and it should be noted that the above preferred embodiments should not be regarded as limiting the present invention. For those skilled in the art, several equivalent substitutions, improvements and modifications can be made without departing from the spirit and scope of the present invention, and these equivalent substitutions, improvements and modifications should also be regarded as the protection scope of the present invention. The embodiments will not be repeated here, and the protection scope of the present invention shall be based on the scope defined by the claims.

Claims

1. A FCCM mode output discharge control method, applied to the light no-load shutdown of a switching power supply, the switching power supply comprising a main switch tube and a synchronous freewheeling tube, characterized in that: The FCCM mode output discharge control method comprises the following steps: A power-off shutdown type identification step, identifying whether the power-off shutdown type is an input voltage non-circuit-breaking type power-off shutdown or an input voltage circuit-breaking type power-off shutdown; The shutdown control strategy execution step executes the corresponding control strategy according to the power-off shutdown type. At the same time, during the shutdown process, the negative current peak value when the output flows back to the input is detected in real time, and the negative current peak value is limited within the negative current threshold: When the power-off shutdown type is the input voltage non-circuit-breaking power-off shutdown, the control strategy is: at the moment of the switch power supply shutdown, all the switch tubes in the switch power supply continue to work, while reducing the duty cycle of the main switch tube and increasing the duty cycle of the synchronous freewheeling tube, and the output voltage flows back to the input side and finally feeds back to the input power supply. After the first time period, all the switch tubes in the switch power supply are turned off to complete the shutdown; When the power-off shutdown type is the input voltage circuit-breaking power-off shutdown, the control strategy is: when the input voltage drops to the undervoltage shutdown threshold, the switch tube connected to the positive end of the input voltage is turned off first, and the remaining switch tubes continue to work. At the same time, the duty cycle of the synchronous freewheeling tube is increased, and the output voltage flows back to the input side, causing the input voltage to rise. Until the input voltage drops to the undervoltage shutdown threshold again, all the switch tubes in the switching power supply are turned off to complete the shutdown.

2. The FCCM mode output discharge control method according to claim 1, characterized in that: When the input voltage first drops to the undervoltage shutdown threshold, and within the set time, the input voltage is higher than the first threshold, the power-off shutdown type is identified as input voltage circuit-breaking power-off shutdown, otherwise it is input voltage non-circuit-breaking power-off shutdown.

3. The FCCM mode output discharge control method according to claim 2, characterized in that: The first threshold is greater than the under-voltage shutdown threshold.

4. The FCCM mode output discharge control method according to claim 1, characterized in that: The input voltage non-circuit-breaking type power-off shutdown includes input power shutdown and Ctrl shutdown; the input voltage circuit-breaking type power-off shutdown includes a shutdown in which an air switch or a circuit breaker disconnects the power supply circuit.

5. The FCCM mode output discharge control method according to claim 1, characterized in that: When the input voltage non-circuit-breaking power-off shutdown is an input power shutdown, the first duration timing starts when the input voltage first drops to the undervoltage shutdown threshold; When the input voltage non-circuit-breaking power-off shutdown is a Ctrl shutdown, the first duration timing starts when the Ctrl shutdown reaches a shutdown threshold.

6. According to the FCCM mode output discharge control method of claim 1, the switching power supply further includes a synchronous rectifier tube, characterized in that: When the absolute value of the negative current peak sampling value is greater than the absolute value of the negative current threshold, the synchronous rectifier is turned off cycle by cycle.

7. The FCCM mode output discharge control method according to claim 6, characterized in that: The absolute value of the negative current threshold is greater than zero, and is less than or equal to the maximum forward current that the switching power supply can withstand.

8. An FCCM mode output discharge control device, applied to the light no-load shutdown of a switching power supply, the switching power supply comprising a main switch tube and a synchronous freewheeling tube, characterized in that: The FCCM mode output discharge control device comprises the following units: A power-off shutdown type identification unit, used to identify whether the power-off shutdown type is an input voltage non-circuit-breaking type power-off shutdown or an input voltage circuit-breaking type power-off shutdown; The shutdown control strategy execution unit is used to execute the corresponding control strategy according to the power-off shutdown type. At the same time, during the shutdown process, the negative current peak value when the output flows back to the input is detected in real time, and the negative current peak value is limited within the negative current threshold: When the power-off shutdown type is the input voltage non-circuit-breaking power-off shutdown, the control strategy is: at the moment of the switch power supply shutdown, all the switch tubes in the switch power supply continue to work, while reducing the duty cycle of the main switch tube and increasing the duty cycle of the synchronous freewheeling tube, and the output voltage flows back to the input side and finally feeds back to the input power supply. After the first time period, all the switch tubes in the switch power supply are turned off to complete the shutdown; When the power-off shutdown type is the input voltage circuit-breaking power-off shutdown, the control strategy is: when the input voltage drops to the undervoltage shutdown threshold, the switch tube connected to the positive end of the input voltage is turned off first, and the remaining switch tubes continue to work. At the same time, the duty cycle of the synchronous freewheeling tube is increased, and the output voltage flows back to the input side, causing the input voltage to rise. Until the input voltage drops to the undervoltage shutdown threshold again, all the switch tubes in the switching power supply are turned off to complete the shutdown.

9. A switching power supply, characterized in that: It includes the FCCM mode output discharge control device as described in claim 8.

10. The switching power supply according to claim 9, characterized in that: The adopted topology is a buck single-stage topology, or a cascade topology including a buck and an isolation switch power supply circuit; or a cascade topology including a buck-boost and an isolation switch power supply circuit.

11. The switching power supply according to claim 10, characterized in that: The isolating switch power supply circuit is a bridge circuit, or a push-pull circuit, or an LLC circuit.

12. The switching power supply according to claim 10, characterized in that: When the main switch tube is turned on, the inductor is magnetized.

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