Switching power supply and charging device

Abstract

The embodiment of the utility model discloses a switching power supply and a charging device, and belongs to the technical field of electronics. The switching power supply comprises a first switching circuit, a transformer, a control circuit, a feedback circuit, a second switching circuit and an oscillating circuit. Wherein the first switching circuit is arranged in a current path of a primary coil of the transformer, and a first output end of the control circuit is connected with a control end of the first switching circuit; the first switching circuit is configured to switch the on-off state of a current path of the primary coil according to a switching control signal received by a control end; a first end of the feedback circuit is connected with a first secondary coil of the transformer, and the feedback circuit is configured to output a turn-off signal through a second end when short-circuit current in the first secondary coil is detected. According to the invention, when the switching power supply is short-circuited, the switching power supply stops working, so that internal devices are prevented from being damaged.

Description

Technical Field

[0001] The present application relates to the field of electronic technology, and in particular to a switching power supply and a charging device. Background Art

[0002] With the development of new energy technologies, DC charging piles are gradually appearing in daily life. In order to improve the safety and stability of DC charging piles, it is necessary to isolate the high-voltage circuit at the input end from the low-voltage circuit at the output end through an isolated power supply to reduce electrical interference and the risk of electric shock to users.

[0003] In the current industry, the function of isolating power supply is often achieved through switching power supply. Although this method is low-cost, when a short circuit occurs at the output end of the switching power supply, it is easy to damage the internal components of the switching power supply, causing the switching power supply to fail completely. Utility Model Content

[0004] The present application provides a switching power supply and a charging device, which can stop the switching power supply from working when a short circuit occurs at the output end of the switching power supply, thereby avoiding damage to internal components. The technical solution is as follows:

[0005] In one aspect, a switching power supply is provided, the switching power supply comprising a first switching circuit, a transformer, a control circuit, a feedback circuit, a second switching circuit and an oscillation circuit; wherein,

[0006] The first switch circuit is arranged in the current path of the primary coil of the transformer, the first output end of the control circuit is connected to the control end of the first switch circuit, and the first switch circuit is configured to switch the on / off state of the current path of the primary coil according to a switch control signal received by the control end;

[0007] A first end of the feedback circuit is connected to a first secondary winding of the transformer, and the feedback circuit is configured to output a shutdown signal through a second end when a short-circuit current in the first secondary winding is detected;

[0008] The control end of the second switch circuit is connected to the second end of the feedback circuit, the first end of the second switch circuit is connected to the power end of the oscillation circuit, the second end of the second switch circuit is connected to the power supply voltage line of the oscillation circuit, the output end of the oscillation circuit is connected to the first input end of the control circuit, and the second switch circuit is configured to cut off the current path between the first end and the second end when the control end receives the shutdown signal, so that the oscillation circuit stops providing the oscillation signal to the control circuit, and the control circuit that loses the supply of the oscillation signal stops providing the switch control signal to the first switch circuit, so that the switching power supply does not work.

[0009] Optionally, the feedback circuit includes a voltage divider circuit, a three-terminal voltage regulator and a photocoupler;

[0010] The first end of the voltage divider circuit is connected to the first end of the feedback circuit, the second end of the voltage divider circuit is connected to the control end of the three-terminal voltage regulator tube, the voltage divider circuit is configured to provide a voltage divider signal proportional to the voltage signal to the second end based on the voltage signal of the first end, and the three-terminal voltage regulator tube is configured to disconnect the current path of the three-terminal voltage regulator tube when the voltage value of the voltage divider signal is lower than the voltage threshold;

[0011] The light emitting element of the photocoupler is arranged in the current path of the three-terminal voltage regulator tube, and the light receiving element of the photocoupler is connected to the second end of the feedback circuit to provide the shutdown signal to the second end of the feedback circuit when the light emitting element is in the off state.

[0012] Optionally, the control end of the second switch circuit is connected to a power supply voltage line of the oscillation circuit.

[0013] Optionally, a power supply voltage line of the oscillation circuit is connected to the second output terminal of the control circuit, so that the control circuit provides a power supply voltage to the oscillation circuit through the power supply voltage line.

[0014] Optionally, the second switch circuit includes a P-type transistor, a first resistor, a second resistor and a first capacitor;

[0015] The first end of the P-type transistor is connected to the first end of the second switch circuit, the second end of the P-type transistor is connected to the second end of the second switch circuit, the control end of the P-type transistor is connected to one end of the first resistor, the other end of the first resistor is respectively connected to one end of the second resistor and one end of the first capacitor, the other end of the second resistor is connected to the control end of the second switch circuit, and the other end of the first capacitor is connected to the common end of the second switch circuit.

[0016] Optionally, the P-type transistor is a PNP-type triode or a P-type MOS (Metal Oxide Semiconductor) transistor.

[0017] Optionally, the switching power supply further includes an internal power supply circuit;

[0018] The input end of the internal power supply circuit is connected to the second secondary coil of the transformer, and the output end of the internal power supply circuit is connected to the power supply end of the control circuit;

[0019] The internal power supply circuit is configured to power the control circuit through an electrical signal on the second secondary coil.

[0020] Optionally, the switching power supply further comprises a peak absorption circuit, and the peak absorption circuit is respectively connected to two ends of the primary coil of the transformer;

[0021] The peak absorption circuit is configured to absorb the current on the primary coil of the transformer at the moment when the current path of the primary coil of the transformer changes from being on to being off, so as to protect the first switch circuit.

[0022] Optionally, the switching power supply has a power output port, and the power output port is connected to the first secondary coil.

[0023] On the other hand, a charging device is provided, the device comprising the switching power supply described in the above aspect.

[0024] The technical solution provided by this application can at least bring the following beneficial effects:

[0025] In the embodiment of the present application, when the output of the switching power supply is short-circuited, the second switching circuit is disconnected, so that the oscillation circuit stops providing an oscillation signal to the control circuit, thereby causing the control circuit to stop outputting a switch control signal to disconnect the current path of the primary coil of the transformer, thereby preventing the circuit devices inside the switching power supply from bearing greater energy, causing excessive power consumption, heating, and damage when the output of the switching power supply is short-circuited, thereby truly protecting the switching power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 It is a structural schematic diagram of a switching power supply provided in an embodiment of the present application;

[0028] Figure 2 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0029] Figure 3 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0030] Figure 4 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0031] Figure 5 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0032] Figure 6 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0033] Figure 7 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0034] Figure 8 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0035] Fig. 9 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0036] Fig.10 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0037] Fig.11 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0038] Fig.12 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0039] Fig.13 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0040] Fig.14 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0041] Fig.15 is a structural schematic diagram of another switching power supply provided in an embodiment of the present application;

[0042] Fig.16 It is a circuit connection diagram of a switching power supply provided in an embodiment of the present application. DETAILED DESCRIPTION

[0043] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the implementation methods of the present application will be further described in detail below in conjunction with the accompanying drawings.

[0044] Before explaining the switching power supply provided in the embodiment of the present application in detail, the application scenarios involved in the embodiment of the present application are first introduced.

[0045] With the development of new energy technologies, DC charging piles are gradually appearing in daily life. In order to improve the safety and stability of DC charging piles, it is necessary to isolate the high-voltage circuit at the input end from the low-voltage circuit at the output end through an isolated power supply to reduce electrical interference and the risk of electric shock to users. In the current industry, the function of isolated power supply is often achieved through switching power supply.

[0046] In a switching power supply, the control circuit can output a switch control signal to switch the on / off state of the current path of the primary coil of the transformer. The control circuit in the current switching power supply is usually designed using a switching power supply chip, but some switching power supply chips lack a short-circuit protection mechanism. For example, for a switching power supply designed based on the 284X and 384X series switching power supply chips, when the output of the switching power supply is short-circuited, the switching power supply chip will still output a switch drive signal with a large duty cycle, so that the primary coil of the transformer is still in a working state, causing the primary coil of the transformer to store a large amount of electrical energy. However, due to the short circuit of the output of the switching power supply, the electrical energy stored in the primary coil of the transformer cannot be output to the external load, which will cause the switch tube, transformer and other circuit devices in the switching power supply to bear a lot of energy, and it is easy to have over-power consumption, heating, damage, etc., which will cause the switching power supply to fail completely.

[0047] Based on this, an embodiment of the present application provides a switching power supply, which includes a second switching circuit, and the second switching circuit can realize a short-circuit protection function. When the output of the switching power supply is short-circuited, the second switching circuit is disconnected, so that the oscillation circuit stops providing an oscillation signal to the control circuit, thereby causing the control circuit to stop outputting a switch control signal to disconnect the current path of the primary coil of the transformer, thereby preventing the circuit components inside the switching power supply from bearing a large amount of energy, causing the circuit components to over-power, heat, or be damaged when the output of the switching power supply is short-circuited, and can truly protect the switching power supply.

[0048] Next, the switching power supply provided in the embodiment of the present application is explained in detail.

[0049] The present application embodiment provides a switching power supply, such as Figure 1As shown, the switching power supply includes a first switching circuit 1, a transformer 2, a control circuit 3, a feedback circuit 4, a second switching circuit 5 and an oscillation circuit 6. The first switching circuit 1 is arranged in the current path of the primary coil 21 of the transformer 2, the first output terminal 3a of the control circuit 3 is connected to the control terminal 1a of the first switching circuit, and the first switching circuit 1 is configured to switch the on-off state of the current path of the primary coil 21 according to the switch control signal received by the control terminal 1a. The first terminal 4a of the feedback circuit 4 is connected to the first secondary coil 22 of the transformer 2, and the feedback circuit 4 is configured to output a shutdown signal through the second terminal 4b when a short-circuit current in the first secondary coil 22 is detected. The control end 5a of the second switch circuit 5 is connected to the second end 4b of the feedback circuit 4, the first end 5b of the second switch circuit 5 is connected to the power supply end 6a of the oscillation circuit 6, the second end 5c of the second switch circuit 5 is connected to the power supply voltage line 66 of the oscillation circuit 6, the output end 6b of the oscillation circuit 6 is connected to the first input end 3b of the control circuit 3, and the second switch circuit 5 is configured to cut off the current path between the first end 5b and the second end 5c when the control end 5a receives a shutdown signal, so that the oscillation circuit 6 stops providing an oscillation signal to the control circuit 3, and the control circuit 3 that loses the oscillation signal supply stops providing a switch control signal to the first switch circuit 1, so that the switch power supply does not work.

[0050] In practical applications, the primary coil 21 can be connected to an external power source, and the first secondary coil 22 can be connected to an external load, so that the voltage of the external power source is converted into the voltage required by the external load through the switching power supply, thereby providing power to the external load. Figure 1 As shown, the first end 21a of the primary coil 21 is connected to the controlled end 1b of the first switch circuit 1, the second end 21b of the primary coil 21 is connected to the external power supply, and the first switch circuit 1 is also connected to the common end. The first end 22a of the first secondary coil 22 is respectively connected to the external load and the first end 4a of the feedback circuit 4, and the second end 22b of the first secondary coil 22 is connected to the common end.

[0051] It should be noted that the output short circuit of the switching power supply described below refers to the output short circuit from the first secondary coil 22 to the external load, the output voltage of the switching power supply described below refers to the voltage provided by the switching power supply to the external load, and the power supply voltage of the oscillation circuit described below is the voltage on the power supply voltage line of the oscillation circuit.

[0052] When the switching power supply is working normally, the second switching circuit 5 is turned on, the power supply terminal 6a of the oscillation circuit 6 is connected to the power supply voltage line of the oscillation circuit 6 through the second switching circuit 5, and the output terminal 6b of the oscillation circuit 6 outputs an oscillation signal. In this way, the first input terminal 3b of the control circuit 3 has an oscillation signal input, and the first output terminal 3a of the control circuit 3 outputs a switch control signal. The switch control signal causes the on-off state of the first switch circuit 1 to be continuously switched, thereby realizing the on-off state of the current path of the primary coil 21 to be continuously switched, thereby realizing the function of the switching power supply. For example, the switch control signal is a periodic square wave signal. In each cycle, when the switch control signal is at a high level, the first switch circuit 1 is turned on, and when the switch control signal is at a low level, the first switch circuit 1 is disconnected.

[0053] When the output of the switching power supply is short-circuited, the first secondary coil 22 is short-circuited. The feedback circuit 4 can detect the short-circuit of the first secondary coil 22. When the first secondary coil 22 of the switching power supply is short-circuited, the feedback circuit 6 provides a shutdown signal to the control terminal 5a of the second switching circuit 5. After the control terminal 5a receives the shutdown signal, the second switching circuit 5 disconnects the current path between the first terminal 5b and the second terminal 5c, and the power supply terminal 6a of the oscillation circuit 6 loses power supply, so the oscillation circuit 6 no longer provides an oscillation signal to the control circuit 3. After the control circuit 3 loses the supply of the oscillation signal, it stops providing the switch control signal to the first switching circuit 1, so that the first switching circuit 1 remains in a disconnected state, and then the current path of the primary coil 21 of the transformer 2 remains in a disconnected state.

[0054] The oscillation signal may be a sawtooth wave signal, the switch control signal may be a PWM (Pulse Width Modulation) signal or other signal with high and low level changes, and the shutdown signal may be a high level signal. Of course, these signal waveforms are only examples, and in actual applications, these signal waveforms need to be determined according to the design of each circuit.

[0055] The power supply voltage line of the oscillating circuit 6 can be connected to the external power supply of the switching power supply, or can be connected to an output terminal of a circuit inside the switching power supply with a stable voltage output. After the switching power supply is powered on, there is a stable voltage on the power supply voltage line of the oscillating circuit 6.

[0056] In the embodiment of the present application, when the output of the switching power supply is short-circuited, the current path of the primary coil of the transformer remains disconnected, thereby preventing the secondary side of the transformer from not working while the primary side is still working when the output of the switching power supply is short-circuited, causing the circuit devices inside the switching power supply to bear greater energy, thereby causing the circuit devices to consume too much power, generate heat, and be damaged, etc., thereby truly protecting the switching power supply and improving the life of the switching power supply.

[0057] In some embodiments, Figure 2 As shown, the control circuit 3 has the above-mentioned first input terminal 3b and first output terminal 3a, and further has a second output terminal 3c. The power supply voltage line of the oscillation circuit 6 is connected to the second output terminal 3c of the control circuit 3, so that the control circuit 3 provides the power supply voltage to the oscillation circuit 6 through the power supply voltage line. Figure 2 As shown, the control circuit 3 often also has a power supply terminal 3d, which can be connected to an external power supply. That is, when the control circuit 3 is powered on, its second output terminal 3c can output the power supply voltage of the oscillation circuit 6.

[0058] The above describes the working process of the switching power supply provided by the embodiment of the present application. Next, possible structures of the first switching circuit 1, the control circuit 3, the feedback circuit 4, the second switching circuit 5 and the oscillation circuit 6 are respectively described.

[0059] 1. First switch circuit 1

[0060] In some embodiments, such as Figure 3 As shown, the first switch circuit 1 includes an N-type transistor Q2, a third resistor R3 and a fourth resistor R4. The first end Q2a of the N-type transistor Q2 is connected to the controlled end 1b of the first switch circuit 1, the second end Q2b of the N-type transistor Q2 is connected to one end of the third resistor R3 and the common end of the first switch circuit 1, and the control end Q2c of the N-type transistor Q2 is respectively connected to the other end of the third resistor R3 and one end of the fourth resistor R4. The other end of the fourth resistor R4 is connected to the control end 1a of the first switch circuit 1.

[0061] When the first output terminal 3a of the control circuit 3 outputs a high level, a current will flow from the first output terminal 3a of the control circuit 3 through the fourth resistor R4 and the third resistor R3 to the ground in sequence. At this time, the voltage difference across the third resistor R3 is the voltage difference between the control terminal Q2c and the second terminal Q2b of the N-type transistor Q2. When the voltage difference across the third resistor R3 is greater than the conduction voltage of the N-type transistor Q2, the voltage difference between the control terminal Q2c and the second terminal Q2b of the N-type transistor Q2 is greater than the conduction voltage, and it can be seen from the flow direction of the current that the voltage of the control terminal Q2c of the N-type transistor Q2 is greater than the voltage of the second terminal Q2b, which satisfies the conduction condition of the N-type transistor Q2, so the N-type transistor Q2 is turned on. When the first output terminal 3a of the control circuit 3 outputs a low level, the above conduction condition is not met, and the N-type transistor Q2 is turned off.

[0062] Since the first output terminal 3 a of the control circuit 3 outputs a high-low level signal, the on-off state of the N-type transistor Q2 is continuously switched, thereby causing the on-off state of the first switch circuit 1 to be continuously switched.

[0063] It can be seen from the above content that the third resistor R3 can divide the voltage output by the first output terminal 3a of the control circuit 3, so that when the first output terminal 3a of the control circuit 3 outputs a high level, the voltage difference between the control terminal Q2c and the second terminal Q2b of the N-type transistor Q2 is greater than the turn-on voltage, so that the N-type transistor Q2 can be turned on.

[0064] The fourth resistor R4 is a current limiting resistor, which can limit the driving current of the N-type transistor Q2 to prevent excessive current from damaging the N-type transistor Q2. In addition, adjusting the size of the fourth resistor R4 can adjust the reaction sensitivity of the N-type transistor Q2 when it is turned on and off. When the resistance value of the fourth resistor R4 is large, the reaction sensitivity of the N-type transistor Q2 becomes low. On the contrary, when the resistance value of the fourth resistor R4 is small, the reaction sensitivity of the N-type transistor Q2 will become high. The specific principle can be referred to the introduction of the first resistor R1 in the second switch circuit 5 later, which will not be expanded here.

[0065] In some embodiments, the N-type transistor Q2 is an N-channel MOS transistor, the drain of the MOS transistor serves as the first end Q2a of the N-type transistor Q2, the source of the MOS transistor serves as the second end Q2b of the N-type transistor Q2, and the gate of the MOS transistor serves as the control end Q2c of the N-type transistor Q2.

[0066] In this case, when the voltage of the gate of the MOS tube is greater than the voltage of the source, and the voltage difference between the gate and the source is greater than the turn-on voltage of the MOS tube, the MOS tube can be turned on.

[0067] In some embodiments, the N-type transistor Q2 is an NPN-type transistor, the collector of the transistor serves as the first end Q2a of the N-type transistor Q2, the emitter of the transistor serves as the second end Q2b of the N-type transistor Q2, and the base of the transistor serves as the control end Q2c of the N-type transistor Q2.

[0068] In this case, when the voltage of the base of the transistor is greater than the voltage of the emitter, and the voltage difference between the base and the emitter is greater than the turn-on voltage of the transistor, the transistor can be turned on.

[0069] In practical applications, more or fewer devices may be used to implement the first switch circuit 1 according to application requirements.

[0070] 2. Control circuit 3

[0071] In some embodiments, Figure 4As shown, the control circuit 3 is implemented by a switch power chip 33 of the 284X and 384X series. The signal input pin RT / CT of the switch power chip 33 is connected to the first input terminal 3b of the control circuit 3, the output pin DRV of the switch power chip 33 is connected to the first output terminal 3a of the control circuit 3, and the power pin VCC of the switch power chip 33 is connected to the power terminal 3d of the control circuit 3. When the oscillation circuit 6 generates an oscillation signal, the signal input pin RT / CT of the switch power chip 33 receives the oscillation signal, and then the switch power chip 33 generates a switch control signal based on the oscillation signal and provides it to the first switch circuit 1 through the output pin DRV, so that the first switch circuit 1 is continuously switched on and off through the switch control signal. The switch control signal generated by the switch power chip 33 is a periodic PWM signal.

[0072] When the output of the switching power supply is short-circuited, the second switching circuit 5 is disconnected, the oscillation circuit 6 cannot be powered, and thus cannot generate an oscillation signal. When the oscillation circuit 6 does not generate an oscillation signal, the signal input pin RT / CT of the switching power supply chip 33 is suspended. At this time, the switching power supply chip 33 cannot generate a switch control signal, and the output pin DRV will output an electrical signal with a constant voltage to keep the first switching circuit 1 disconnected.

[0073] In some embodiments, Figure 4 As shown, if the second output terminal 3 c of the control circuit 3 is connected to the power supply voltage line 66 of the oscillation circuit 6 , the voltage reference pin VREF of the switching power chip 33 is connected to the second output terminal 3 c of the control circuit 3 .

[0074] When the voltage of the power pin VCC of the switch power chip 33 reaches the start-up voltage of the switch power chip 33 , the switch power chip 33 is officially started. At this time, the voltage reference pin VREF outputs a reference voltage as the power voltage of the oscillation circuit 6 .

[0075] In some embodiments, Figure 4 As shown, the second end 4b of the feedback circuit 4 is also connected to the voltage detection pin VSEN of the switching power chip 33, so that the feedback circuit 4 feeds back the output voltage of the switching power supply to the switching power chip 33. In this case, since the second end 4b of the feedback circuit 4 is connected to the control end 5a of the second switching circuit 5, the voltage detection pin VSEN of the switching power chip 33 and the control end 5a of the second switching circuit 5 are also connected together.

[0076] When the output voltage of the switching power supply is less than the voltage required by the external load, the switching power supply chip 33 increases the duty cycle of the switch control signal to increase the duration of the conduction of the second switch circuit 5, thereby increasing the duration of the conduction of the current path of the primary coil 21, so that the switching power supply can obtain more electric energy supplied by the external power supply, thereby increasing the output voltage of the switching power supply. When the output voltage of the switching power supply is greater than the voltage required by the external load, the switching power supply chip 33 reduces the duty cycle of the switch drive signal to reduce the duration of the conduction of the second switch circuit 5, thereby reducing the duration of the conduction of the current path of the primary coil 21, so that the electric energy input by the external power supply is reduced, thereby reducing the output voltage of the switching power supply.

[0077] In practical applications, other types of chips or other circuit devices may be used to implement the control circuit 3 according to application requirements.

[0078] In one example, the control circuit 2 includes a processor and a memory storing a processor executable program. The processor may include one or more ASICs (Application-Specific Integrated Circuit), DSPs (Digital Signal Processor), DSPDs (Digital Signal Processing Device), PLDs (Programable Logic Device), Field Programmable Gate Arrays (Field Programmable Gate Array, FPGA), controllers, microcontrollers, microprocessors or other electronic components or circuit structures with equivalent functions.

[0079] 3. Feedback circuit 4

[0080] In some embodiments, Figure 5 As shown, the feedback circuit 4 includes a voltage divider circuit 41, a three-terminal voltage regulator 42 and a photocoupler 43. The first end 41a of the voltage divider circuit 41 is connected to the first end 4a of the feedback circuit 4, the second end 4b of the voltage divider circuit 41 is connected to the control end R of the three-terminal voltage regulator 42, the voltage divider circuit 41 is configured to provide a voltage divider signal proportional to the voltage signal to the second end 41b based on the voltage signal of the first end 41a, and the three-terminal voltage regulator 42 is configured to disconnect the current path of the three-terminal voltage regulator 42 when the voltage value of the voltage divider signal is lower than the voltage threshold; the light-emitting element 431 of the photocoupler 43 is arranged in the current path of the three-terminal voltage regulator 42, and the light-receiving element 432 of the photocoupler 43 is connected to the second end 4b of the feedback circuit 4 to provide a shutdown signal to the second end 4b of the feedback circuit 4 when the light-emitting element 431 is in the off state.

[0081] When the output of the switching power supply is short-circuited, the current on the first secondary coil 22 is very large, and the output voltage of the switching power supply is low level, so the voltage signal of the first end 41a of the voltage divider circuit 41 is low level, and the second end 41b of the voltage divider circuit 41 provides a voltage divider signal proportional to the voltage signal, so the voltage divider signal provided by the second end 4b of the voltage divider circuit 41 is also low level, and the voltage value of the voltage divider signal is lower than the voltage threshold of the three-terminal voltage regulator 42, and the current path of the three-terminal voltage regulator 42 is disconnected. In this way, the current path of the light-emitting element 431 of the photocoupler 43 is also disconnected, and the light-emitting element 431 is turned off, resulting in the current path of the light-receiving element 432 of the photocoupler 43 being unable to conduct, so that the second end 4b of the feedback circuit 4 is in a suspended state.

[0082] The light emitting element 431 may be a light emitting diode, and the light receiving element 432 may be a phototransistor. The three-terminal voltage regulator tube 42 may be replaced by other circuit devices with a switching function, such as a transistor.

[0083] In some embodiments, Figure 5 As shown, the control end 5a of the second switch circuit 5 is connected to the power supply voltage line 66 of the oscillation circuit 6. Since the second end 4b of the feedback circuit 4 is connected to the control end 5a of the second switch circuit 5, when the current path of the light receiving element 432 of the photocoupler 43 is not conducting, the second end 4b of the feedback circuit 4 is connected to the power supply voltage of the oscillation circuit 6, and the second end 4b of the feedback circuit 4 is in a high level state.

[0084] In some embodiments, Figure 6 As shown, the feedback circuit 4 includes a photocoupler U1 whose light emitting element is a light emitting diode and whose light receiving element is a phototransistor, a fifth resistor R5, a sixth resistor R6, a second capacitor C2, a three-terminal voltage regulator U2, a seventh resistor R7, and an eighth resistor R8. The collector of the phototransistor of the photocoupler U1 is connected to the second end 4b of the feedback circuit 4, the emitter of the phototransistor of the photocoupler U1 is connected to the common end, the anode of the light emitting diode of the photocoupler U1 is connected to one end of the seventh resistor R7, and the cathode of the light emitting diode of the photocoupler U1 is connected to the cathode K of the three-terminal voltage regulator U2. The other end of the seventh resistor R7 is respectively connected to one end of the fifth resistor R5 and the first end 4a of the feedback circuit 4. The eighth resistor R8 is connected between the anode and the cathode of the light emitting diode of the photocoupler U1, and the second capacitor C2 is connected between the collector and the emitter of the phototransistor of the photocoupler U1. The control end R of the three-terminal voltage regulator U2 is connected to one end of the fifth resistor R5 and one end of the sixth resistor R6, and the anode A of the three-terminal voltage regulator U2 is connected to the common end. The other end of the sixth resistor R6 is connected to the common end.

[0085] Among them, the fifth resistor R5 and the sixth resistor R6 form a voltage divider circuit 41. When the output voltage of the switching power supply is greater than the voltage required by the external load, the output voltage can make the voltage difference across the sixth resistor R6 greater than the reverse conduction voltage of the three-terminal voltage regulator U2 (i.e., the above-mentioned voltage threshold) after being divided by the fifth resistor R5 and the sixth resistor R6, that is, the voltage of the control terminal R of the three-terminal voltage regulator U2 is greater than the reverse conduction voltage of the three-terminal voltage regulator U2. At this time, the three-terminal voltage regulator U2 can be reversely conducted, so that the current path of the light-emitting diode of the photocoupler U1 can also be turned on, and then the photosensitive transistor of the photocoupler U1 can also be turned on. The second terminal 4b of the feedback circuit 4 is equivalent to being connected to the common terminal and is at a low level. At this time, the switch control signal output by the control circuit 3 will shorten the conduction time of the current path of the primary coil 21, so that the external power supply reduces the power input to the switching power supply, so that the output voltage of the switching power supply can be reduced.

[0086] After the output voltage of the switching power supply is reduced to a certain value (usually a little less than the voltage required by the external load), the voltage difference across the sixth resistor R6 is still greater than the reverse conduction voltage of the three-terminal voltage regulator U2, the three-terminal voltage regulator U2 can still be reversely conducted, and the light-emitting diode of the photoelectric coupler U1 can still be turned on. However, since the output voltage of the switching power supply is reduced at this time, the current flowing through the light-emitting diode of the photoelectric coupler U1 is also reduced, and the light intensity emitted by the light-emitting diode of the photoelectric coupler U1 is not enough to fully turn on the photosensitive transistor of the photoelectric coupler U1. Compared with when it is fully turned on, the voltage at both ends of the photosensitive transistor connected in parallel with the second capacitor C2 increases, so the second capacitor C2 will be charged, and the second end 4b of the feedback circuit 4 gradually changes from a low level to a high level. When the second end 4b of the feedback circuit 4 is at a high level, the switch control signal output by the control circuit 3 will make the conduction time of the current path of the primary coil 21 longer, so that the switching power supply can obtain more electric energy input by the external power supply, and the output voltage of the switching power supply becomes higher again. Then, when the output voltage is greater than the voltage required by the external load again, the phototransistor of the photocoupler U1 is turned on again, the second capacitor C2 is discharged, the second terminal 4b of the feedback circuit 4 changes from a high level to a low level, and the switch control signal output by the control circuit 2 shortens the time for the current path of the primary coil 21 to be turned on, thereby reducing the output voltage of the switching power supply again. In this way, the output voltage of the switching power supply can fluctuate around the voltage required by the external load.

[0087] When the output of the switching power supply is short-circuited, the current on the first secondary coil 22 is very large, and almost no circuit flows through the fifth resistor R5 and the sixth resistor R6. At this time, the voltage on the sixth resistor R6 is almost 0, and the voltage of the control terminal R of the three-terminal voltage regulator U2 cannot reach the reverse conduction voltage of the three-terminal voltage regulator U2. The three-terminal voltage regulator U2 cannot be turned on, so that the light-emitting diode of the photoelectric coupler U1 cannot be turned on, the light-emitting diode of the photoelectric coupler U1 cannot emit light, and the photosensitive transistor of the photoelectric coupler U1 cannot be turned on. At this time, the second terminal 4b of the feedback circuit 4 will be at a high level for a long time, which is the above-mentioned shutdown signal. The control terminal 5a of the second switch circuit 5 is disconnected after receiving the shutdown signal, so that the oscillation circuit 6 stops providing the oscillation signal to the control circuit 3, the control circuit 3 stops outputting the switch control signal, the current path of the primary coil 21 remains disconnected, and the switching power supply stops working.

[0088] In addition, the seventh resistor R7 and the eighth resistor R8 are used for current limiting to prevent excessive current from flowing through the three-terminal voltage regulator U2 and the light-emitting diode of the photocoupler U1 when the output voltage is large, so as to avoid the three-terminal voltage regulator U2 and the photocoupler U1 being damaged by excessive current breakdown. The seventh resistor R7 and the eighth resistor R8 are optional devices.

[0089] Alternatively, if Figure 6 As shown, the feedback circuit 4 also includes a third capacitor C3, a ninth resistor R9, and a fourth capacitor C4. One end of the third capacitor C3 is connected to the cathode K of the three-terminal voltage regulator U2, and the other end is connected to one end of the ninth resistor R9, and the other end of the ninth resistor R9 is connected to the control end R of the three-terminal voltage regulator U2. The fourth capacitor C4 is connected between the cathode K and the control end R of the three-terminal voltage regulator U2.

[0090] The third capacitor C3, the ninth resistor R9, and the fourth capacitor C4 can suppress parasitic parameters in the circuit, so that the feedback circuit 4 can work more stably.

[0091] In practical applications, more or fewer devices may be used to implement the feedback circuit 4 according to application requirements.

[0092] It should be noted that the feedback circuit described in the embodiment of the present application refers to any circuit structure that can change the signal output state of the second end (for example, from a high level to a low level) when a short circuit occurs in the current path where the first end is located, which can be implemented, for example, by referring to the circuit structure of any current detector, voltage detector, or power detector.

[0093] 4. Second switch circuit 5

[0094] In some embodiments, Figure 7As shown, the second switch circuit 5 includes a P-type transistor Q1, a first resistor R1, a second resistor R2 and a first capacitor C1. The first end Q1a of the P-type transistor Q1 is connected to the second end 5c of the second switch circuit 5, the second end Q1b of the P-type transistor Q1 is connected to the first end 5b of the second switch circuit 5, the control end Q1c of the P-type transistor Q1 is connected to one end of the first resistor R1, the other end of the first resistor R1 is respectively connected to one end of the second resistor R2 and one end of the first capacitor C1, the other end of the second resistor R2 is connected to the control end 5a of the second switch circuit 5, and the other end of the first capacitor C1 is connected to the common end of the second switch circuit 5.

[0095] When the voltage at the first terminal Q1a of the P-type transistor Q1 is greater than the voltage at the control terminal Q1c of the P-type transistor Q1, and the difference between the two voltages is greater than the turn-on voltage of the P-type transistor Q1, the P-type transistor Q1 is turned on, otherwise, the P-type transistor Q1 is turned off. It should be noted that the turn-on voltage of the P-type transistor Q1 is less than the power supply voltage of the oscillation circuit 6.

[0096] The first resistor R1 is a current limiting resistor. When the P-type transistor Q1 is turned on, the current direction on the P-type transistor Q1 is from the first end Q1a to the control end Q1c, and from the first end Q1a to the second end Q1b, and the current flowing from the first end Q1a to the control end Q1c is the driving current. As the magnitude of the driving current changes, the magnitude of the current flowing from the first end Q1a to the second end Q1b will also change. The first resistor R1 is located on the flow path of the driving current (the driving current will eventually flow back to the common end). Compared with the case where there is no first resistor R1, the first resistor R1 can increase the resistance on the flow path of the driving current, thereby reducing the driving current, and further reducing the current flowing from the first end Q1a to the second end Q1b in the P-type transistor Q1. Therefore, the first resistor R1 can prevent excessive current from damaging the P-type transistor Q1.

[0097] In addition, the above-mentioned driving current is actually the current corresponding to the power supply voltage of the oscillation circuit 6, which flows through the first terminal Q1a of the P-type transistor Q1 to the control terminal Q1c and finally flows back to the common terminal. The size of the first resistor R1 limits the resistance size on this current path, so that the speed at which the current flows through the P-type transistor Q1, which will limit the speed at which the P-type transistor Q1 obtains the driving current, thereby limiting the speed at which the P-type transistor Q1 is turned on. When the P-type transistor Q1 is disconnected, the current inside the P-type transistor Q1 needs to flow to the common terminal through the control terminal Q1c to complete the current release, so that the P-type transistor Q1 is completely turned off, and the size of the first resistor R1 also limits the resistance size on the release path of the current, thereby limiting the release speed of the current inside the P-type transistor Q1.

[0098] Therefore, by adjusting the resistance of the first resistor R1, the reaction sensitivity of the P-type transistor Q1 when it is turned on and off can be adjusted. When the resistance of the first resistor R1 is large, the reaction sensitivity of the P-type transistor Q1 becomes low. On the contrary, when the resistance of the first resistor R1 is small, the reaction sensitivity of the P-type transistor Q1 becomes high.

[0099] The second resistor R2 is also a current limiting resistor. When the switching power supply is working normally, it can be seen from the above introduction to the feedback circuit 4 that the voltage of the second terminal 4b of the feedback circuit 4 will switch back and forth between high and low levels, and the time for maintaining the high / low level after each switch is very short. When the second terminal 4b of the feedback circuit 4 is at a high level, the current corresponding to the power supply voltage of the oscillation circuit 6 will flow to the first capacitor C1 through the second resistor R2, thereby charging the first capacitor C1, so that the voltage difference across the first capacitor C1 increases, and then the voltage of the control terminal Q1c of the P-type transistor Q1 increases. When the switching power supply is working normally, the P-type transistor Q1 needs to remain turned on, and the voltage of its control terminal Q1c cannot be too high. Compared with the case where there is no second resistor R2, the second resistor R2 can increase the resistance on the flow path of the current flowing to the first capacitor C1, so that the current flowing to the first capacitor C1 can be reduced, so that the voltage across the first capacitor will not rise too high each time it is charged, so that the voltage of the control terminal Q1c of the P-type transistor Q1 will not be too high, so that the P-type transistor Q1 can be kept turned on.

[0100] In addition, since the size of the second resistor R2 can limit the size of the current flowing to the first capacitor C1, the speed of charging and discharging the first capacitor C1 can be adjusted by adjusting the resistance of the second resistor R2, that is, the reaction sensitivity of the charging and discharging of the first capacitor C1 can be adjusted. When the resistance of the second resistor R2 is large, the reaction sensitivity of the first capacitor C1 will become low, and when the resistance of the second resistor R2 is small, the reaction sensitivity of the first capacitor C1 will be high.

[0101] The operation process of the second switch circuit 5 is described below.

[0102] After the switch power supply is powered on, the power supply voltage of the oscillating circuit 6 can reach the first capacitor C1 through the second resistor R2. The first capacitor C1 is equivalent to a short circuit in a short time just after powering on. In this way, the control terminal Q1c of the P-type transistor Q1 is equivalent to being connected to the common terminal through the first resistor R1. The voltage of the first terminal Q1a of the P-type transistor Q1 is the power supply voltage of the oscillating circuit 6, that is, the voltage of the first terminal Q1a of the P-type transistor Q1 is the power supply voltage, and the control terminal Q1c is connected to the common terminal. The voltage of the first terminal Q1a of the P-type transistor Q1 is obviously greater than the voltage of the control terminal Q1c of the P-type transistor Q1, and the difference between the two voltages is greater than the threshold voltage. Therefore, the P-type transistor Q1 is turned on, that is, the second switch circuit 5 is turned on.

[0103] During the normal operation of the switching power supply, the voltage of the second terminal 4b of the feedback circuit 4 will switch back and forth between high and low levels, and the time for maintaining the high / low level after each switch is very short. When the second terminal 4b of the feedback circuit 4 is at a high level, the power supply voltage of the above-mentioned oscillation circuit 6 charges the first capacitor C1 through the second resistor R2, and the voltage across the first capacitor C1 gradually increases. When the second terminal 4b of the feedback circuit 4 is at a low level, the first capacitor C1 discharges outward, and the voltage across the two ends gradually decreases. The first capacitor C1 will discharge outward after a very short charging process each time, and when the first capacitor C1 is charged, the second resistor R2 will also divide the voltage, so the voltage of the control terminal Q1c of the P-type transistor Q1 will not be too high, and can always be less than the power supply voltage of the oscillation circuit 6, and the voltage difference with the power supply voltage of the oscillation circuit 6 is greater than the conduction voltage of the P-type transistor Q1, and the P-type transistor Q1 can remain on.

[0104] When the output of the switching power supply is short-circuited, the second terminal 4b of the feedback circuit 4 will be in a high level state for a long time, so that the first capacitor C1 will be charged for a long time, causing the voltage of the control terminal Q1c of the P-type transistor Q1 to continue to increase, but the voltage of the first terminal Q1a of the P-type transistor Q1 is always the power supply voltage of the oscillation circuit 6, and the voltage does not change. When the difference between the voltage of the first terminal Q1a and the control terminal Q1c of the P-type transistor Q1 is less than its own conduction voltage, the P-type transistor Q1 is disconnected, that is, the second switch circuit 5 is disconnected.

[0105] Optionally, the P-type transistor Q1 is a PNP-type triode or a P-type MOS transistor.

[0106] In some embodiments, the P-type transistor Q1 is a PNP-type triode, the emitter of which serves as the first terminal Q1a, the collector of which serves as the second terminal Q1b, and the base of which serves as the control terminal Q1c.

[0107] In this case, when the voltage of the emitter of the transistor is greater than the voltage of the base, and the voltage difference between the emitter and the base is greater than the turn-on voltage of the transistor, the transistor can be turned on, so that the current of the emitter of the transistor can flow to the collector.

[0108] In some embodiments, the P-type transistor Q1 is a P-channel MOS transistor, the source of which serves as the first terminal Q1a, the drain of which serves as the second terminal Q1b, and the gate of which serves as the control terminal Q1c.

[0109] In this case, when the voltage of the source of the MOS tube is greater than the voltage of the gate and the voltage difference between the source and the gate is greater than the turn-on voltage of the MOS tube, the MOS tube can be turned on so that the current of the source of the MOS tube can flow to the drain.

[0110] The embodiment of the present application does not limit the specific sizes of the first resistor R1 and the second resistor R2, which can be set according to actual application requirements.

[0111] The first capacitor C1 may be an electrolytic capacitor or other types of capacitors, which is not limited in the embodiment of the present application.

[0112] In practical applications, more or fewer devices may be used to implement the second switch circuit 5 according to application requirements.

[0113] It should be noted that the switching circuit (first switching circuit, second switching circuit) described in the embodiment of the present application refers to any circuit structure that can change the on-off state between the first end and the second end based on a control end signal, which can be implemented, for example, based on at least one switching device (transistor, field effect transistor, relay, controllable diode, photocoupler, etc.) or a combination thereof.

[0114] 5. Oscillation circuit 6

[0115] In some embodiments, Figure 8 As shown, the oscillation circuit 6 includes a tenth resistor R10 and a fifth capacitor C5. One end of the tenth resistor R10 is connected to the power supply terminal 6a of the oscillation circuit 6, and the other end is respectively connected to one end of the fifth capacitor C5 and the output terminal 6b of the oscillation circuit 6, and the other end of the fifth capacitor C5 is connected to the common terminal.

[0116] When the second switch circuit 5 is turned on, the voltage on the power supply voltage line 66 of the oscillation circuit 6 can charge the fifth capacitor C5 through the tenth resistor R10. When the charging threshold of the fifth capacitor C5 is reached, the fifth capacitor C5 is discharged through its own internal current source, and then the next charging and discharging is performed again. In this way, the oscillation circuit 6 can output a sawtooth wave signal to the first input terminal 3b of the control circuit 3 through continuous charging and discharging.

[0117] After the second switch circuit 5 is disconnected, the oscillation circuit 6 cannot be powered, and the oscillation circuit 6 cannot output a sawtooth wave signal. The first input terminal 3b of the control circuit 3 has no signal input and is in a suspended state.

[0118] The sizes of the tenth resistor R10 and the fifth capacitor C5 determine the frequency of the sawtooth wave signal output by the oscillation circuit 6, and the frequency of the sawtooth wave signal is determined by the circuit structure of the control circuit 3. Therefore, the sizes of the tenth resistor R10 and the fifth capacitor C5 can be determined according to the circuit structure of the control circuit 3, and the embodiments of the present application do not limit the sizes of the two.

[0119] In practical applications, more or fewer devices may be used to implement the oscillation circuit 6 according to application requirements.

[0120] In some embodiments, Fig. 9 As shown, the switching power supply further includes a peak absorption circuit 7, which is respectively connected to both ends of the primary coil 21 of the transformer 2. The peak absorption circuit 7 is configured to absorb the current on the primary coil 21 of the transformer 2 at the moment when the current path of the primary coil 21 of the transformer 2 changes from on to off, so as to protect the first switching circuit 1.

[0121] In some embodiments, Fig.10 As shown, the peak absorption circuit 7 includes a sixth capacitor C6, an eleventh resistor R11, a twelfth resistor R12, a thirteenth resistor R13, and a first diode D1. The sixth capacitor C6, the eleventh resistor R11, the twelfth resistor R12, and the thirteenth resistor R13 are connected in parallel, and one end is connected to the second end 21b of the primary coil 21, and the other end is connected to the cathode of the first diode D1. The anode of the first diode D1 is connected to the first end 21a of the primary coil 21.

[0122] When the current path of the primary coil 21 is turned on, the voltage of the first end 21a of the primary coil 21 is lower than the voltage of the second end 21b. At the moment when the current path of the primary coil 21 changes from on to off, a self-induced electromotive force is generated on the primary coil 21, so that the voltage on the primary coil 21 is reversed, so that the voltage of the first end 21a of the primary coil 21 is higher than the voltage of the second end 21b, and the current on the primary coil 21 is very large at this moment. At this time, the current on the primary coil 21 can flow through the first diode D1 and be absorbed by the sixth capacitor C6. The current absorbed by the sixth capacitor C6 can be consumed by the eleventh resistor R11, the twelfth resistor R12, and the thirteenth resistor R13 connected in parallel therewith. In this way, the protection of the first switch circuit 1 can be achieved to prevent the components in the first switch circuit 1 from being damaged by excessive current breakdown.

[0123] Optionally, the eleventh resistor R11, the twelfth resistor R12, and the thirteenth resistor R13 may be replaced by only one or two resistors, or more resistors may be connected in parallel, which is not limited in the embodiment of the present application.

[0124] In practical applications, more or fewer devices may be used to implement the spike absorption circuit 7 according to application requirements.

[0125] In some embodiments, Fig.11 As shown, the switching power supply further includes an internal power supply circuit 8. An input terminal 8a of the internal power supply circuit 8 is connected to the second secondary coil 23 of the transformer 2, and an output terminal 8b of the internal power supply circuit 8 is connected to the power supply terminal 3d of the control circuit 3; the internal power supply circuit 8 is configured to supply power to the control circuit 3d through the electrical signal on the second secondary coil 23.

[0126] like Fig.11 As shown, one end of the second secondary coil 23 is connected to the input end 8a of the internal power supply circuit 8, and the other end is connected to the common end.

[0127] Similar to the first secondary coil 22, during normal operation of the switching power supply, the voltage across the second secondary coil 23 will also continuously reverse following the voltage across the primary coil 21, so the direction of the electrical signal output by the second secondary coil 23 will continuously change, that is, the second secondary coil 23 outputs an AC electrical signal.

[0128] The internal power supply circuit 8 can convert the AC signal output by the second secondary coil 23 into a DC signal, and output it to the power supply terminal 3d of the control circuit 3. In this way, after the switching power supply is powered on for a period of time and during normal operation, the internal power supply circuit 8 can use the energy that the switching power supply has obtained from the external power supply to power the control circuit 3, thereby reducing the power consumption of the external power supply.

[0129] In some embodiments, Fig.12 As shown, the internal power supply circuit 8 includes a second diode D2 and a seventh capacitor C7. The anode of the second diode D2 is connected to the first end 23a of the second secondary coil 23, and the cathode of the second diode D2 is connected to the output end 8b of the internal power supply circuit 8 and one end of the seventh capacitor C7. The other end of the seventh capacitor C7 is connected to the common end. The first end 23a of the second secondary coil 23 and the first end 31a of the primary coil 21 are the same end.

[0130] The second diode D2 can rectify the alternating current on the second secondary coil 23 into direct current. The seventh capacitor C7 is an energy storage capacitor.

[0131] During the normal operation of the switching power supply, the voltage at both ends of the second secondary coil 23 follows the voltage at both ends of the primary coil 21 and continuously reverses. When the voltage at the first end 23a of the second secondary coil 23 is higher than the voltage at the second end 23b, the second diode D2 can be turned on, and the electric energy on the second secondary coil 23 can be released to the power supply end 3d of the control circuit 3 through the second diode D2 to power the control circuit 3. At this time, the seventh capacitor C7 is charged. When the voltage at the second end 23b of the second secondary coil 23 is higher than the voltage at the first end 23a, the second diode D2 is not turned on, and the electric energy on the second secondary coil 23 cannot be released to the power supply end 3d of the control circuit 3 through the second diode D2. At this time, the electric energy stored in the seventh capacitor C7 powers the control circuit 3.

[0132] Alternatively, if Fig.13 As shown, the internal power supply circuit 8 further includes a fourteenth resistor R14. The fourteenth resistor R14 is connected between the anode of the second diode D2 and the first end 23a of the second secondary coil 23. The fourteenth resistor R14 is a current limiting resistor, which can prevent the second diode D2 from being damaged by excessive current input into the second diode D2.

[0133] Alternatively, if Fig.13 As shown, the internal power supply circuit 8 also includes an eighth capacitor C8. The eighth capacitor C8 is connected between the two ends of the seventh capacitor C7. The eighth capacitor C8 is a filter capacitor that can filter out clutter (such as noise in the circuit), so that the voltage supplied by the internal power supply circuit 8 to the control circuit 3 is more stable.

[0134] In practical applications, more or fewer devices may be used to implement the internal power supply circuit 8 according to application requirements.

[0135] As can be seen from the above description, the first secondary coil 22 can be connected to an external load to supply power to the external load. That is, in some embodiments, the switching power supply has a power output port, and the power output port is connected to the first secondary coil 22 .

[0136] The power output port may include a positive power output port and a common terminal, may include a negative power output port and a common terminal, or may include a positive power output port, a negative power output port and a common terminal.

[0137] For example, Fig.14 As shown, the first end 22a of the first secondary coil 22 is connected to the positive power output port A, and the second end 22b is connected to the common end.

[0138] For example, Fig.15As shown, the first secondary coil 22 includes a first secondary sub-coil 221 and a second secondary sub-coil 222, one end of the first secondary sub-coil 221 is connected to the positive power output port A, and the other end is connected to the common end, and one end of the second secondary sub-coil 222 is connected to the negative power output port B, and the other end is connected to the common end. The external load can select a suitable power output port according to demand. The connection of the feedback circuit 4 in the figure is only an example.

[0139] In some embodiments, the secondary side of the transformer 2 includes a plurality of secondary coils, and the first secondary coil 22 is a main coil among the plurality of secondary coils.

[0140] When one of the secondary coils is short-circuited, the load corresponding to the secondary coil is equivalent to infinity, so the main energy of the secondary side of the transformer 2 is consumed by the short-circuited secondary coil, and the corresponding output voltages of the other secondary coils will be pulled down. Therefore, when any secondary coil is short-circuited, the output voltage corresponding to the main coil (the first secondary coil 22) can be pulled down, thereby ultimately achieving the purpose of disconnecting the current path of the primary coil 21.

[0141] It should be noted that all the above-mentioned connection relationships can be direct connections or indirect connections. For example, the first secondary coil 22 and the power output port of the switching power supply can be connected through an energy storage circuit, which is not limited in the embodiments of the present application.

[0142] In addition, in the embodiment of the present application, the control circuit provides the power supply voltage of the oscillation circuit as an example. The power supply voltage of the oscillation circuit can also be provided by other connection terminals or circuit structures (such as a voltage converter, a power management module, etc.).

[0143] In summary, the switching power supply can be Fig.16 As shown, the switching power supply includes Figure 3 The first switch circuit shown, Figure 4 The control circuit shown, Figure 6 The feedback circuit shown, Figure 7 The second switch circuit shown, Figure 8 The oscillator circuit shown, Fig.10 The spike absorption circuit shown, Fig.13 The internal power supply circuit shown. Among them, the switch power chip 33 constituting the control circuit is a switch power chip of the 284X or 384X series. Among them, the voltage reference pin VREF of the switch power chip 33 outputs the power supply voltage of the oscillation circuit, the voltage detection pin VSEN of the switch power chip 33 is respectively connected to the second end 4b of the feedback circuit and the control end 5a of the second switch circuit, and the voltage reference pin VREF and the voltage detection pin VSEN of the switch power chip 33 are connected through a resistor R15. Please refer to the above description for the internal structure of each circuit, which will not be repeated here. Fig.16 The switching power supply shown can realize all the functions described above.

[0144] It should be noted that the above steps and circuit structures are only optional embodiments of the present application, and each of the above implementations can be appropriately modified according to actual application requirements, and components can be added, deleted and / or replaced on the basis of the illustrated structure. For example, in any of the above circuit structures, any resistor can be implemented by using a plurality of resistors having a series structure and / or a parallel structure, and any capacitor can be implemented by using a plurality of capacitors having a series structure and / or a parallel structure.

[0145] It should be noted that the high level (corresponding to the logical true value of "1" or "TRUE") and the low level (corresponding to the logical true value of "0" or "FALSE") are two voltage value ranges that do not have an intersection. It should be understood that the high level and the low level are voltage ranges specified to distinguish different logical values ​​(such as "1" and "0"), and can be set according to application requirements in specific application scenarios. In one example, the high level is specified as a voltage with a voltage value greater than 3.2V, and the low level is specified as a voltage with a voltage value less than 0.5V. In addition, it should be understood that the high level and the low level can correspond to multiple different voltage values, respectively, so two different voltage values ​​may both belong to the high level or both belong to the low level, and the same voltage value may belong to the high level and the low level for different circuit nodes or different signals, respectively, and the embodiments of the present application do not limit this.

[0146] In the embodiment of the present application, the switching power supply includes a second switching circuit, and the second switching circuit can realize a short-circuit protection function. When the output of the switching power supply is short-circuited, the second switching circuit is disconnected, so that the oscillation circuit stops providing an oscillation signal to the control circuit, thereby causing the control circuit to stop outputting a switch control signal to disconnect the current path of the primary coil of the transformer, thereby preventing the circuit components inside the switching power supply from bearing a large amount of energy, causing the circuit components to consume too much power, generate heat, or be damaged when the output of the switching power supply is short-circuited, and thus truly realizing the protection of the switching power supply.

[0147] The embodiment of the present application further provides a charging device, which includes a switching power supply. The switching power supply can realize any of the functions in the previous embodiment. The charging device is, for example, a charging pile device for charging electric vehicles.

[0148] The terms used in the embodiments of the present disclosure are only used to explain the embodiments of the present disclosure, and are not intended to limit the present disclosure. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meanings understood by people with ordinary skills in the field to which the present disclosure belongs. The words "first", "second", "third" and similar words used in the patent application specification and claims of the present disclosure do not indicate any order, quantity or importance, and the words "first", "second" and the like do not limit them to be different, but are only used to distinguish different components. Similarly, similar words such as "one" or "one" do not indicate a quantitative limit, but indicate that there is at least one. Similar words such as "include" or "comprise" mean that the elements or objects appearing in front of "include" or "comprise" include the elements or objects listed after "include" or "comprise" and their equivalents, and do not exclude other elements or objects. Similar words such as "connect" or "connected" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. “Up”, “down”, “left”, “right”, etc. are only used to indicate relative position relationships. When the absolute position of the described object changes, the relative position relationship may also change accordingly.

[0149] In addition, it should be understood that the "at least one" mentioned herein refers to one or more, and "multiple" refers to two or more. In the description of the embodiments of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B; "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships, for example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone.

[0150] The above-mentioned embodiments are provided for the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A switching power supply, characterized in that: The switching power supply includes a first switching circuit, a transformer, a control circuit, a feedback circuit, a second switching circuit and an oscillation circuit; wherein, The first switch circuit is arranged in the current path of the primary coil of the transformer, the first output end of the control circuit is connected to the control end of the first switch circuit, and the first switch circuit is configured to switch the on / off state of the current path of the primary coil according to a switch control signal received by the control end; A first end of the feedback circuit is connected to a first secondary winding of the transformer, and the feedback circuit is configured to output a shutdown signal through a second end when a short-circuit current in the first secondary winding is detected; The control end of the second switch circuit is connected to the second end of the feedback circuit, the first end of the second switch circuit is connected to the power end of the oscillation circuit, the second end of the second switch circuit is connected to the power supply voltage line of the oscillation circuit, the output end of the oscillation circuit is connected to the first input end of the control circuit, and the second switch circuit is configured to cut off the current path between the first end and the second end when the control end receives the shutdown signal, so that the oscillation circuit stops providing the oscillation signal to the control circuit, and the control circuit that loses the supply of the oscillation signal stops providing the switch control signal to the first switch circuit, so that the switching power supply does not work.

2. The switching power supply according to claim 1, characterized in that: The feedback circuit includes a voltage divider circuit, a three-terminal voltage regulator and a photoelectric coupler; The first end of the voltage divider circuit is connected to the first end of the feedback circuit, the second end of the voltage divider circuit is connected to the control end of the three-terminal voltage regulator tube, the voltage divider circuit is configured to provide a voltage divider signal proportional to the voltage signal to the second end based on the voltage signal of the first end, and the three-terminal voltage regulator tube is configured to disconnect the current path of the three-terminal voltage regulator tube when the voltage value of the voltage divider signal is lower than the voltage threshold; The light emitting element of the photocoupler is arranged in the current path of the three-terminal voltage regulator tube, and the light receiving element of the photocoupler is connected to the second end of the feedback circuit to provide the shutdown signal to the second end of the feedback circuit when the light emitting element is in the off state.

3. The switching power supply according to claim 2, characterized in that: The control end of the second switch circuit is connected to the power supply voltage line of the oscillation circuit.

4. The switching power supply according to any one of claims 1 to 3, characterized in that: The power supply voltage line of the oscillation circuit is connected to the second output terminal of the control circuit, so that the control circuit provides the power supply voltage to the oscillation circuit through the power supply voltage line.

5. The switching power supply according to claim 1, characterized in that: The second switch circuit includes a P-type transistor, a first resistor, a second resistor and a first capacitor; The first end of the P-type transistor is connected to the first end of the second switch circuit, the second end of the P-type transistor is connected to the second end of the second switch circuit, the control end of the P-type transistor is connected to one end of the first resistor, the other end of the first resistor is respectively connected to one end of the second resistor and one end of the first capacitor, the other end of the second resistor is connected to the control end of the second switch circuit, and the other end of the first capacitor is connected to the common end of the second switch circuit.

6. The switching power supply according to claim 5, characterized in that: The P-type transistor is a PNP-type triode or a P-type metal oxide semiconductor MOS transistor.

7. The switching power supply according to claim 1, characterized in that: The switching power supply also includes an internal power supply circuit; The input end of the internal power supply circuit is connected to the second secondary coil of the transformer, and the output end of the internal power supply circuit is connected to the power supply end of the control circuit; The internal power supply circuit is configured to power the control circuit through an electrical signal on the second secondary coil.

8. The switching power supply according to claim 1, characterized in that: The switching power supply further comprises a peak absorption circuit, and the peak absorption circuit is respectively connected to two ends of the primary coil of the transformer; The peak absorption circuit is configured to absorb the current on the primary coil of the transformer at the moment when the current path of the primary coil of the transformer changes from being on to being off, so as to protect the first switch circuit.

9. The switching power supply according to claim 1, characterized in that: The switching power supply has a power output port, and the power output port is connected to the first secondary coil.

10. A charging device, characterized in that: The charging device comprises a switching power supply as claimed in any one of claims 1 to 9.

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