Output circuit and switching power supply

Abstract

The invention discloses an output circuit and a switching power supply, and the output circuit comprises a voltage division circuit, one end of which is connected with a positive DC voltage bus, and the other end of which is connected with a negative DC voltage bus; the first end of the short-circuit protection trigger circuit is connected with one end of the voltage division circuit, the second end is connected with the other end of the voltage division circuit, the third end is connected with a voltage division point of the voltage division circuit, and the fourth end is connected with a switching power supply intermediate voltage output point; when the switching power supply works normally, positive output voltage is generated from the positive voltage to the intermediate voltage output point through the voltage division circuit and the short-circuit protection trigger circuit, and negative output voltage is generated from the negative voltage to the intermediate voltage output point through the voltage division circuit and the short-circuit protection trigger circuit. When the intermediate voltage output point and the positive voltage output point or the intermediate voltage output point and the negative voltage output point of the switching power supply are short-circuited, the short-circuit protection trigger circuit triggers the short-circuit protection circuit to work, and the positive output voltage and the negative output voltage are cut off at the same time. According to the invention, the semiconductor with the driven rear end can be protected.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply circuits, and in particular to an output circuit and a switching power supply. Background Art

[0002] The three-output adjustable circuit is used in circuits that require positive voltage, intermediate voltage, and negative voltage supply.

[0003] One application of this circuit is for driving the gates of transistors such as insulated gate bipolar transistors (IGBTs), silicon carbide (SiC), gallium nitride (GaN), and other metal oxide semiconductor field effect transistors (MOSFETs). These transistors require specific positive and negative gate voltages to turn them on or off. In these cases, the power supply will provide positive (+v), neutral (0V), and negative (-v) voltage supplies, which is achieved by grounding the intermediate voltage supply.

[0004] A known adjustable triple output circuit provides a precise voltage drop between an intermediate voltage output point and either a positive voltage output point or a negative voltage output point by inserting a Zener diode between the appropriate voltage outputs. The remaining voltage is absorbed by a resistor connected in series with the Zener diode. The resistor and Zener diode act as a voltage divider with the midpoint of their connection as the intermediate voltage output. Figure 1 and Figure 2 An example of such a three-output DC voltage supply is provided. However, when a short circuit occurs across the resistor of the voltage divider, the total voltage will be applied across the Zener diode, causing the Zener diode to break down, thereby causing a large current to flow. Although the DC power supply itself has a short-circuit protection function, the current may not be sufficient to trigger the short-circuit protection of the power supply, and the Zener diode may still be damaged due to overvoltage, overcurrent, overheating, etc.

[0005] Based on the above problems, a solution is provided in Chinese invention patent 202180084821.6, as shown in the attached Figure 3 By changing the Zener diode to an adjustable output and adding a current limiting resistor, when a short circuit occurs at both ends of the resistor of the voltage divider, the current limiting resistor can limit the current flowing through the adjustable output, thereby protecting the adjustable output. However, other problems will be introduced: when the intermediate voltage output point is short-circuited with the positive voltage output point or the negative voltage output point, the negative voltage or positive voltage output will be equal to the input power supply. At this time, when the circuit is applied to the gate drive circuit, the voltage output by the driver will follow this voltage, which may cause damage to the transistor due to exceeding the voltage range of the transistor gate.

[0006] Similarly, Chinese invention patent 202211107137.8 also provides a solution to prevent the voltage stabilizing device from being damaged due to exceeding the dissipated power consumption of the device, as shown in the attached Figure 4 When the intermediate voltage point is short-circuited with the positive output voltage point or the negative output voltage point, one of the transistors in the bistable latch circuit will be turned off, thereby protecting the other transistors. However, the same problem exists as the solution provided in Chinese invention patent 202180084821.6. When the intermediate voltage output point is short-circuited with the positive voltage output point or the negative voltage output point, the negative voltage or positive voltage output will be equal to the input power supply. At this time, when the circuit is applied to the gate drive circuit, the voltage output by the driver will follow this voltage, which may cause damage to the transistor due to exceeding the voltage range of the transistor gate. Summary of the invention

[0007] In view of this, the technical problem to be solved by the present invention is to provide an output circuit and a switching power supply, which can realize the conversion of a single-channel power supply with short-circuit protection into a dual-power supply output with positive and negative adjustment. When a short circuit occurs at the middle point, the short-circuit protection of the power supply can be triggered. If a short circuit occurs in either channel, the output of the other channel will also be closed synchronously to protect the semiconductor driven at the back end.

[0008] As a first aspect of the present invention, an embodiment of the output circuit provided is as follows: An output circuit is applied to a switching power supply, the switching power supply comprising a positive DC voltage bus, a negative DC voltage bus, a positive voltage output point, an intermediate voltage output point, a negative voltage output point and a short-circuit protection circuit, one end of the short-circuit protection circuit is simultaneously connected to the positive DC voltage bus and the positive voltage output point of the switching power supply, and the other end is simultaneously connected to the negative DC voltage bus and the negative voltage output point of the switching power supply, wherein the output circuit comprises: A voltage divider circuit, one end of which is used to connect to the positive DC voltage bus, and the other end of which is used to connect to the negative DC voltage bus; A short circuit protection trigger circuit, wherein the first end is connected to one end of the voltage divider circuit, the second end is connected to the other end of the voltage divider circuit, the third end is connected to the voltage dividing point of the voltage divider circuit, and the fourth end is used to connect to the intermediate voltage output point of the switching power supply; When the switching power supply operates normally, a positive output voltage is generated from the positive voltage output point to the intermediate voltage output point of the switching power supply through the voltage divider circuit and the short-circuit protection trigger circuit, and a negative output voltage is generated from the negative voltage output point to the intermediate voltage output point of the switching power supply through the voltage divider circuit and the short-circuit protection trigger circuit; When a short circuit occurs between the intermediate voltage output point and the positive voltage output point of the switching power supply or between the intermediate voltage output point and the negative voltage output point, the short circuit protection trigger circuit triggers the short circuit protection circuit to operate and simultaneously shuts off the positive output voltage and the negative output voltage.

[0009] Preferably, the voltage divider circuit includes a first resistor and a second resistor, and after the first resistor and the second resistor are connected in series, one end of the first resistor and the second resistor is one end of the voltage divider circuit, the other end is the other end of the voltage divider circuit, and the middle connection point is the voltage divider point of the voltage divider circuit.

[0010] Preferably, the voltage divider circuit includes a resistor and a Zener diode, the cathode of the resistor and the Zener diode connected in series is one end of the voltage divider circuit, the anode is the other end of the voltage divider circuit, and the middle connection point is the voltage divider point of the voltage divider circuit.

[0011] Preferably, the short-circuit protection trigger circuit includes a first switch tube, a second switch tube and a resistor, one end of the first switch tube is connected to the first end of the short-circuit protection trigger circuit, the other end of the first switch tube and one end of the second switch tube are simultaneously connected to the fourth end of the short-circuit protection trigger circuit, the other end of the second switch tube is connected to the second end of the short-circuit protection trigger circuit, the control end of the first switch tube and the control end of the second switch tube are simultaneously connected to the third end of the short-circuit protection trigger circuit, and the resistor is connected between one end and the other end of the first switch tube.

[0012] Furthermore, the other end of the second switch tube is connected to the second end of the short-circuit protection trigger circuit through a resistor, a Zener diode or a 431 device.

[0013] Preferably, the first switch tube is an NPN transistor or an N-channel MOS tube; The second switch tube is a PNP transistor or a P-channel MOS tube; For the first switch tube: when it is an NPN transistor, the collector of the NPN transistor is one end, the emitter is the other end, and the base is the control end; when it is an N-channel MOS transistor, the drain of the N-channel MOS transistor is one end, the source is the other end, and the gate is the control end; For the second switch tube: when it is a PNP transistor, the emitter of the PNP transistor is one end, the collector is the other end, and the base is the control end; when it is a P-channel MOS tube, the source of the P-channel MOS tube is one end, the drain is the other end, and the gate is the control end.

[0014] Preferably, the first switch tube is an NPN transistor or an N-channel MOS tube; The second switch tube is an NPN transistor or an N-channel MOS tube; For the first switch tube: when it is an NPN transistor, the collector of the NPN transistor is one end, the emitter is the other end, and the base is the control end; when it is an N-channel MOS transistor, the drain of the N-channel MOS transistor is one end, the source is the other end, and the gate is the control end; For the second switching tube: when it is an NPN transistor, the collector of the NPN transistor is one end, the emitter is the other end, and the base is the control end; when it is an N-channel MOS tube, the drain of the N-channel MOS tube is one end, the source is the other end, and the gate is the control end.

[0015] Preferably, the first switch tube is a PNP transistor or a P-channel MOS tube; The second switch tube is an NPN transistor or an N-channel MOS tube; For the first switch tube: when it is a PNP transistor, the emitter of the PNP transistor is one end, the collector is the other end, and the base is the control end; when it is a P-channel MOS transistor, the source of the P-channel MOS transistor is one end, the drain is the other end, and the gate is the control end; For the second switching tube: when it is an NPN transistor, the collector of the NPN transistor is one end, the emitter is the other end, and the base is the control end; when it is an N-channel MOS tube, the drain of the N-channel MOS tube is one end, the source is the other end, and the gate is the control end.

[0016] Preferably, the first switch tube is a PNP transistor or a P-channel MOS tube; The second switch tube is a PNP transistor or a P-channel MOS tube; For the first switch tube: when it is a PNP transistor, the emitter of the PNP transistor is one end, the collector is the other end, and the base is the control end; when it is a P-channel MOS transistor, the source of the P-channel MOS transistor is one end, the drain is the other end, and the gate is the control end; For the second switch tube: when it is a PNP transistor, the emitter of the PNP transistor is one end, the collector is the other end, and the base is the control end; when it is a P-channel MOS tube, the source of the P-channel MOS tube is one end, the drain is the other end, and the gate is the control end.

[0017] As a second aspect of the present invention, the technical solution of the embodiment of the switching power supply provided is as follows: A switching power supply, comprising a positive DC voltage bus, a negative DC voltage bus, a positive voltage output point, an intermediate voltage output point, a negative voltage output point and a short-circuit protection circuit, wherein one end of the short-circuit protection circuit is simultaneously connected to the positive DC voltage bus and the positive voltage output point of the switching power supply, and the other end is simultaneously connected to the negative DC voltage bus and the negative voltage output point of the switching power supply, wherein: the switching power supply also includes the output circuit described in any one of the first aspects above.

[0018] Preferably, the DC power sources of the positive DC voltage bus and the negative DC voltage bus are from transformer rectifier outputs.

[0019] The specific working principle of the present invention will be analyzed and explained in the specific embodiments, which will not be repeated here. Compared with the prior art solutions, the beneficial effects of the present invention are: A short-circuit protection trigger circuit is added. When the intermediate voltage output point of the switching power supply is short-circuited with the positive voltage output point or the intermediate voltage output point is short-circuited with the negative voltage output point, the short-circuit protection trigger circuit is used to trigger the short-circuit protection circuit to work, and the positive output voltage and the negative output voltage are turned off at the same time. Thus, while a single-channel power supply with short-circuit protection is converted into a dual power supply output with positive and negative adjustment, when a short circuit occurs at the intermediate point, the short-circuit protection of the power supply can be triggered, and when a short circuit occurs in any channel, the output of the other channel will also be synchronously turned off. When used as a gate driver power supply circuit, it can protect the driven semiconductor device when the power supply is short-circuited. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of a three-output power supply circuit in the prior art; Figure 2 It is a schematic diagram of a three-output power supply circuit in the prior art; Figure 3 It is the circuit schematic diagram in the embodiment of Chinese invention patent 202211107137.8; Figure 4 It is the circuit schematic diagram in the embodiment of Chinese invention patent 202180084821.6; Figure 5 is a circuit diagram of a first embodiment of the present invention; Figure 6 is a circuit diagram of a second embodiment of the present invention; Figure 7 is a circuit diagram of a third embodiment of the present invention; Figure 8 is a circuit diagram of a fourth embodiment of the present invention; Fig. 9 is a circuit diagram of a fifth embodiment of the present invention; Fig.10 is a circuit diagram of a sixth embodiment of the present invention; Fig.11 FIG. 4 is a circuit diagram of the seventh embodiment of the present invention. DETAILED DESCRIPTION

[0021] The present invention provides an output circuit and a switching power supply including the output circuit. The switching power supply includes a positive DC voltage bus, a negative DC voltage bus, a positive voltage output point, an intermediate voltage output point, a negative voltage output point and a short-circuit protection circuit, wherein one end of the short-circuit protection circuit is simultaneously connected to the positive DC voltage bus and the positive voltage output point of the switching power supply, and the other end is simultaneously connected to the negative DC voltage bus and the negative voltage output point of the switching power supply. The output circuit includes: a voltage divider circuit, one end of which is used to connect to a positive DC voltage bus, and the other end of which is used to connect to a negative DC voltage bus; a short-circuit protection trigger circuit, a first end of which is connected to one end of the voltage divider circuit, a second end of which is connected to the other end of the voltage divider circuit, a third end of which is connected to a voltage dividing point of the voltage divider circuit, and a fourth end of which is used to connect to an intermediate voltage output point of the switching power supply; when the switching power supply works normally, a positive output voltage is generated from a positive voltage output point to an intermediate voltage output point through the voltage divider circuit and the short-circuit protection trigger circuit, and a negative output voltage is generated from a negative voltage output point to an intermediate voltage output point through the voltage divider circuit and the short-circuit protection trigger circuit; when a short circuit occurs between the intermediate voltage output point and the positive voltage output point of the switching power supply or between the intermediate voltage output point and the negative voltage output point, the short-circuit protection trigger circuit is triggered to operate the short-circuit protection circuit, and the positive output voltage and the negative output voltage are turned off at the same time.

[0022] The present invention realizes the conversion of a single-circuit power supply with short-circuit protection into a dual-power supply output with positive and negative adjustable. When a short circuit occurs at the middle point, the short-circuit protection of the power supply can be triggered, and when a short circuit occurs in either circuit, the output of the other circuit will be synchronously closed.

[0023] It should be noted that the terms "including" and "having" and any variations thereof described in the specification and claims of the present application are intended to cover non-exclusive inclusions. For example, the inclusion of a series of components, unit circuits or control timings is not necessarily limited to those components, unit circuits or control timings clearly listed, but may include components, unit circuits or control timings that are not clearly listed or inherent to these circuits.

[0024] In addition, the embodiments and features of the embodiments in this application may be combined with each other if there is no conflict.

[0025] It should be understood that, in the specification and the claims, when an element is described as being “connected” to another element, the element may be “directly connected” to the other element, or be “connected” to the other element through a third element; when a step is described as being continued to another step, the step may be directly continued to the other step, or be continued to the other step through a third step.

[0026] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. A circuit that simply combines the features of the different embodiments described below also belongs to the core idea of ​​the present invention.

[0027] First embodiment This embodiment provides an output voltage. Figure 5 The circuit diagram of the first embodiment of the present invention, the circuit modules and the connection description are as follows: A positive DC voltage bus DC+ and a negative DC voltage bus DC- are used to be connected to a DC power supply with short-circuit protection; a positive voltage output point Vo+, a negative voltage output point Vo-, and an intermediate voltage output point 0V are three output ports; an adjustable voltage divider circuit is connected between the positive DC voltage bus DC+ and the negative DC voltage bus DC-, wherein the adjustable voltage divider circuit includes a positive voltage divider R101, in this embodiment, the positive voltage divider adopts a resistor device, and a negative voltage divider R103, in this embodiment, the negative voltage divider adopts a resistor device, and the positive voltage divider is connected to the cathode of the negative voltage divider; a short-circuit protection trigger circuit is connected between the positive DC voltage bus DC+ and the negative DC voltage bus DC-, wherein the short-circuit protection trigger circuit includes a first transistor Q101, a second transistor Q102 and a resistor R102, and the first transistor is an NPN A transistor or an N-channel MOS transistor (the attached figure and the connection relationship below only take the NPN transistor as an example), the second transistor is a PNP transistor or a P-channel MOS transistor (the attached figure and the connection relationship below only take the PNP transistor as an example), the bases of the two transistors are connected and connected to the midpoint where the positive voltage divider is connected to the negative voltage divider, the collector of the first transistor is connected to the positive DC voltage bus and serves as a positive voltage output point, the emitter of the first transistor is connected to the emitter of the second transistor and serves as an intermediate voltage output point, the collector of the second transistor is connected to the negative DC bus and serves as a negative voltage output point, and the two ends of the resistor R102 are respectively connected to the collector and emitter of the first transistor; a first capacitor C1 is connected between the positive output voltage point and the intermediate voltage output point, and a second capacitor C2 is connected between the negative output voltage point and the intermediate voltage output point.

[0028] The DC power supply mentioned in the above circuit includes any power supply with short-circuit protection function, DC-DC converter output, AC-DC converter output, transformer rectifier output, etc.

[0029] The working principle of this embodiment is described as follows: (1) Adjustable voltage divider circuit: This circuit is mainly used to set positive and negative output voltages. The resistors R101 and R103 in the circuit play a voltage-dividing role. With the cooperation of the short-circuit protection trigger circuit, a positive output voltage is generated between the positive voltage output point and the intermediate voltage output point, and a negative output voltage is generated between the negative voltage output point and the intermediate voltage output point. Different positive and negative voltage outputs can be set by adjusting the voltage-dividing resistor. At the same time, the power consumption of the power supply can be reduced by appropriately increasing the resistance value of the voltage-dividing resistor. (2) Short circuit protection trigger circuit: This circuit is mainly used to work with the adjustable voltage divider circuit to generate positive output voltage and negative output voltage during normal operation. When the intermediate output voltage point is short-circuited with the positive output voltage point or the negative output voltage point, the short-circuit protection of the DC power supply is triggered, and the other output can be synchronously closed at the same time. The specific analysis is as follows: When the circuit is in normal working state, let the DC power supply voltage (i.e. the voltage of the positive DC voltage bus DC+ to the negative DC voltage bus DC-) be V DC , the voltage between the positive voltage output point and the intermediate voltage output point is V O+ , the voltage between the negative voltage output point and the intermediate voltage output point is V O- , the resistance value of each voltage divider is directly represented by its reference symbol, then the voltage at the middle point between the first voltage divider and the second voltage divider V1=V DC *R103 / (R101+R103), since the base voltage of the second transistor Q102 is V1, if the second transistor Q102 is not turned on, the voltage divided by the resistor R102 is 0 because no current flows through it, and the emitter voltage of the second transistor Q102 is the voltage of the positive DC voltage bus DC+, so the base voltage of the second transistor Q102 is lower than the emitter voltage. By setting the resistance values ​​of the first voltage divider and the second voltage divider, the voltage difference between the emitter and the collector of the second transistor Q102 (i.e. the voltage -V1 of the positive DC voltage bus DC+) can be made greater than its turn-on threshold V EB2 (usually 0.3V~0.7V, depending on the characteristics of the second transistor itself), so the PNP type second transistor Q102 must be turned on. Since the first transistor Q101 and the second transistor Q102 share a common base and emitter, and the first transistor Q101 and the second transistor Q102 have opposite polarities, it can be seen that the first transistor is in the off state, so V O+ =V DC -(V1+V EB2 ), V O- =-(V1+V EB2 It is worth noting that this circuit is used in the transistor drive power supply circuit, and the voltage V O+ Generally, it is set between 15 and 20V, and the voltage V O-Generally, it is set between -3V and -9V. O+ =V DC -(V1+V EB2 ) and V O- =-(V1+V EB2 ), it can be seen that under this application condition, V1 is generally set to be greater than 2.3V, that is, during normal operation, the second transistor Q102 is turned on and the first transistor Q101 is turned off; the base-to-collector voltage V BC =V1>0, that is, the base voltage of the second transistor Q102 is higher than the collector voltage. It can be seen that the second transistor Q102 works in the amplification region. At this time, the V EB is easily affected by the emitter-to-collector current flowing through the second transistor Q102, causing V O+ 、V O+ The output voltage is unstable, and the improvement example is shown in the seventh embodiment; When the intermediate voltage output point and the positive voltage output point are short-circuited (i.e. V O+ =0V), the base voltage of the first transistor Q101 is still lower than the emitter voltage, so the first transistor Q101 is still in the off state, and the base voltage of the second transistor Q102 is lower than the emitter voltage and is still in the on state. At this time, it is equivalent to a short circuit between the positive DC voltage bus and the negative DC voltage bus. The short-circuit current path is positive DC voltage bus → positive output voltage point → intermediate voltage output point → second transistor Q102 → negative DC voltage bus, thereby triggering the short-circuit protection of the DC power supply itself. At this time, the voltage V between the positive DC voltage bus DC+ and the negative DC voltage bus DC- DC =0V, and because V O+ =V DC -(V1+V EB )=0V, so V O- =-(V1+V EB ) = 0V, so that when the intermediate voltage output point and the positive voltage output point are short-circuited, V O- =0V, V O+ =0V, that is, if the circuit is short-circuited, the other circuit will be shut down synchronously. Moreover, when the intermediate voltage output point and the positive voltage output point are short-circuited, the emitter and collector of the second transistor Q102 are equivalent to being directly connected across the positive and negative buses of the DC power supply. At this time, the base of the second transistor can be current-limited by the voltage-dividing resistor R101, thereby preventing the current flowing from the emitter to the collector of the second transistor from exceeding the rated current of the second transistor and causing damage. When the intermediate voltage output point and the negative voltage output point are short-circuited (i.e. V O-=0V), the emitter voltage of the second transistor Q102 is pulled to the voltage of the negative DC voltage bus DC-, which is lower than V1, so that the PNP second transistor Q102 is turned off. At this time, the base voltage of the first transistor Q101 is V1, and the emitter voltage is the voltage of the negative DC voltage bus DC-. By setting the resistance values ​​of the first voltage divider and the second voltage divider, the voltage difference between the base and the emitter of the first transistor Q101 (i.e., the voltage of V1-negative DC voltage bus DC-) is greater than its turn-on threshold V EB1 (usually 0.3V~0.7V, depending on the characteristics of the second transistor itself), at this time, the NPN type first transistor Q101 is turned on, and the short-circuit current path is positive DC voltage bus → positive output voltage point → first transistor Q101 → intermediate voltage output point → negative DC voltage bus, triggering the short-circuit protection of the DC power supply, that is, V DC =0V, and because V O- =0V, so V O+ =V DC -(V1+V EB2 )=0V, so that when the intermediate voltage output point and the negative voltage output point are short-circuited, V O- =0V, V O+ =0V, that is, a short circuit occurs in this path, and the other path will be shut down synchronously. Moreover, when a short circuit occurs between the intermediate voltage output point and the negative voltage output point, the emitter and collector of the first transistor Q101 are equivalent to being directly connected across the positive and negative buses of the DC power supply. At this time, the base of the first transistor Q101 can be current limited by the voltage-dividing resistor R101, thereby preventing the current flowing from the emitter to the collector of the first transistor Q101 from exceeding the rated current of the first transistor Q101 and causing damage.

[0030] Please continue to see Figure 5 A resistor R102 is also connected in parallel between the collector and emitter of the first transistor Q101. The resistor R102 is mainly used as a pull-up resistor in this implementation and the following embodiments to prevent the emitter / collector of the first transistor and the second transistor from floating to the ground, which may cause the first transistor and the second transistor to be unable to be reliably turned off or turned on under the above working conditions; in addition, it also prevents the intermediate output point from floating to cause output instability.

[0031] Second embodiment This embodiment provides an output voltage. Figure 6 : is a circuit schematic diagram of the second embodiment of the present invention. The difference between this embodiment and the first embodiment is that: the first transistor Q101 is an NPN triode or an N-channel MOS tube, the second transistor Q102 is an NPN triode or an N-channel MOS tube, Figure 6The collector of the first transistor is connected to the positive DC voltage bus and serves as a positive voltage output point, the emitter of the first transistor is connected to the collector of the second transistor and serves as an intermediate voltage output point, and the emitter of the second transistor is connected to the negative DC bus and serves as a negative voltage output point.

[0032] Figure 6 and Figure 5 The difference is that the polarity of the second transistor Q102 is different, and the emitter of the second transistor Q102 is connected to the negative DC voltage bus DC-. By analyzing the voltage state of the base to the emitter of the first transistor Q101 and the second transistor Q102 in different states, it can also be obtained that the circuit is in a normal working state, and when the intermediate voltage output point and the positive voltage output point are short-circuited, the second transistor Q102 is turned on and the first transistor Q101 is turned off, and when the intermediate voltage output point and the negative voltage output point are short-circuited, the second transistor Q102 is turned off and the first transistor Q101 is turned on, thereby achieving the purpose of the invention.

[0033] Third embodiment This embodiment provides an output voltage. Figure 7 This is a circuit schematic diagram of the third embodiment of the present invention. The difference between this embodiment and the first and second embodiments is that: the first transistor Q101 is a PNP transistor or a P-channel MOS transistor, the second transistor Q102 is an NPN transistor or an N-channel MOS transistor, the emitter of the first transistor is connected to the positive DC voltage bus and serves as a positive voltage output point, the collector of the first transistor is connected to the collector of the second transistor and serves as an intermediate voltage output point, and the emitter of the second transistor is connected to the negative DC bus and serves as a negative voltage output point.

[0034] Figure 6 and Figure 5 The difference is that the polarities of the first transistor Q101 and the second transistor Q102 are exchanged, and the first transistor Q101 and the second transistor Q102 are changed to common collectors. By analyzing the voltage states of the base to the emitter of the first transistor Q101 and the second transistor Q102 in different states, it can also be obtained that the circuit is in a normal working state, and when the intermediate voltage output point and the positive voltage output point are short-circuited, the second transistor Q102 is turned on and the first transistor Q101 is turned off, and when the intermediate voltage output point and the negative voltage output point are short-circuited, the second transistor Q102 is turned off and the first transistor Q101 is turned on, thereby achieving the purpose of the invention.

[0035] Fourth embodiment This embodiment provides an output voltage. Figure 8This is a circuit schematic diagram of the fourth embodiment of the present invention. The difference between this embodiment and the first, second and third embodiments is that: the first transistor Q101 is a PNP transistor or a P-channel MOS transistor, the second transistor Q102 is a PNP transistor or a P-channel MOS transistor, the emitter of the first transistor is connected to the positive DC voltage bus and serves as a positive voltage output point, the collector of the first transistor is connected to the emitter of the second transistor and serves as an intermediate voltage output point, and the collector of the second transistor is connected to the negative DC bus and serves as a negative voltage output point.

[0036] Figure 8 and Figure 5 The difference is that the polarity of the first transistor Q101 is different, and the emitter of the first transistor Q101 is connected to the positive DC voltage bus DC+. By analyzing the voltage state of the base to the emitter of the first transistor Q101 and the second transistor Q102 in different states, it can also be obtained that the circuit is in a normal working state, and when the intermediate voltage output point and the positive voltage output point are short-circuited, the second transistor Q102 is turned on and the first transistor Q101 is turned off, and when the intermediate voltage output point and the negative voltage output point are short-circuited, the second transistor Q102 is turned off and the first transistor Q101 is turned on, thereby achieving the purpose of the invention.

[0037] Fifth embodiment This embodiment provides an output voltage. Fig. 9 : is a circuit principle diagram of the fifth embodiment of the present invention. The difference between this embodiment and the first embodiment is that the negative voltage divider in the adjustable voltage divider circuit is adjusted from the resistor R103 to the Zener diode D101.

[0038] In this embodiment, the voltage from the positive voltage output point to the intermediate voltage output point is equal to the voltage across the resistor R101 minus the voltage drop V from the emitter to the base of the second transistor. eb The voltage from the intermediate voltage output point to the negative voltage output point is equal to the voltage across the Zener diode D101 plus the voltage drop V from the emitter to the base of the second transistor. eb Since the voltage across the Zener diode can remain almost unchanged and is almost unaffected by the DC power supply voltage within a certain range, the voltage from the intermediate voltage output point to the negative voltage output point can remain relatively stable.

[0039] This embodiment is particularly suitable for applications where the voltage from the intermediate voltage output point to the negative voltage output point is a critical voltage and must be kept accurate. This embodiment is also applicable to the second, third, and fourth embodiments.

[0040] Sixth embodiment This embodiment provides an output voltage. Fig.10: is a circuit principle diagram of the sixth embodiment of the present invention. The difference between this embodiment and the first embodiment is that the positive voltage divider in the adjustable voltage divider circuit is adjusted from the resistor R101 to the Zener diode D101.

[0041] In this embodiment, the voltage from the positive voltage output point to the intermediate voltage output point is equal to the voltage across D101 minus the voltage drop V from the emitter to the base of the second transistor. eb The voltage from the intermediate voltage output point to the negative voltage output point is equal to the voltage across the resistor R103 plus the voltage drop V from the emitter to the base of the second transistor. eb , since the voltage across the Zener diode can remain almost unchanged and is almost unaffected by the DC power supply voltage within a certain range, the voltage from the positive voltage output point to the intermediate voltage output point can remain relatively stable.

[0042] This embodiment is particularly suitable for applications where the voltage from the positive voltage output point to the intermediate voltage output point is a critical voltage and must be kept accurate. This embodiment is also applicable to the second, third, and fourth embodiments.

[0043] Seventh embodiment This embodiment provides an output voltage. Fig.11 : is a circuit schematic diagram of the sixth embodiment of the present invention. This embodiment is an improved solution of the first embodiment, and is different from the first embodiment in that: the collector of the second transistor is connected to the negative DC voltage bus through a series resistor R104.

[0044] It can be seen from the analysis of the first embodiment that when there is no short circuit at the intermediate output voltage point, the circuit is in a normal working state, the first transistor is in a closed state, and the second transistor is in an open state and works in the amplification region. Since the second transistor works in the amplification region, the voltage drop V eb susceptible to the emitter-to-collector current I flowing through the second transistor ec As a result, the voltage from the positive voltage output point to the intermediate voltage output point and the voltage from the intermediate voltage output point to the negative output voltage point will be affected by I ec impact.

[0045] In view of the above problem, the collector of the second transistor is connected to the negative DC voltage bus through a series resistor R104, which can increase the collector voltage of the second transistor, make the collector voltage greater than the base voltage, and the emitter voltage greater than the base voltage. The second transistor works in the saturation region, which can reduce the emitter-to-collector current I of the second transistor. ec Influence on output voltage: This embodiment is also applicable to the second, third, fourth, fifth and sixth embodiments, and the resistor R104 may be replaced by a Zener diode or a 431 device to achieve the same purpose.

[0046] Eighth embodiment The present embodiment provides a switching power supply, which includes a positive DC voltage bus, a negative DC voltage bus, a positive voltage output point, an intermediate voltage output point, a negative voltage output point and a short-circuit protection circuit, one end of the short-circuit protection circuit is simultaneously connected to the positive DC voltage bus and the positive voltage output point of the switching power supply, and the other end is simultaneously connected to the negative DC voltage bus and the negative voltage output point of the switching power supply, wherein: the switching power supply also includes any output circuit of the first to seventh embodiments.

[0047] The switching power supply of this embodiment includes any one of the output circuits in the first to seventh embodiments, and realizes the conversion of a single-channel short-circuit protected power supply into a dual-power supply output with adjustable positive and negative directions. When a short circuit occurs at the middle point, the short-circuit protection of the power supply can be triggered, and when a short circuit occurs in any one channel, the output of the other channel will be synchronously shut down.

[0048] In a specific implementation, a first capacitor C1 is connected between the positive voltage output point and the intermediate voltage output point, and a second capacitor C2 is connected between the negative voltage output point and the intermediate voltage output point. When the circuit is used to power a power transistor (not shown), a large transient gate drive current can be provided. When the circuit is not used to drive a power transistor, the first and second capacitors can be omitted. The DC power supply of the positive DC voltage bus and the negative DC voltage bus can come from the transformer rectifier output. The intermediate voltage can be 0V.

[0049] The above are merely implementation modes of the present invention. It should be particularly pointed out that the above implementation modes should not be regarded as limitations of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An output circuit, applied to a switching power supply, the switching power supply comprising a positive DC voltage bus, a negative DC voltage bus, a positive voltage output point, an intermediate voltage output point, a negative voltage output point and a short-circuit protection circuit, one end of the short-circuit protection circuit is simultaneously connected to the positive DC voltage bus and the positive voltage output point of the switching power supply, and the other end is simultaneously connected to the negative DC voltage bus and the negative voltage output point of the switching power supply, characterized in that: The output circuit comprises: A voltage divider circuit, one end of which is used to connect to the positive DC voltage bus, and the other end of which is used to connect to the negative DC voltage bus; A short circuit protection trigger circuit, wherein the first end is connected to one end of the voltage divider circuit, the second end is connected to the other end of the voltage divider circuit, the third end is connected to the voltage dividing point of the voltage divider circuit, and the fourth end is used to connect to the intermediate voltage output point of the switching power supply; When the switching power supply operates normally, a positive output voltage is generated from the positive voltage output point to the intermediate voltage output point of the switching power supply through the voltage divider circuit and the short-circuit protection trigger circuit, and a negative output voltage is generated from the negative voltage output point to the intermediate voltage output point of the switching power supply through the voltage divider circuit and the short-circuit protection trigger circuit; When a short circuit occurs between the intermediate voltage output point and the positive voltage output point of the switching power supply or between the intermediate voltage output point and the negative voltage output point, the short circuit protection trigger circuit triggers the short circuit protection circuit to operate and simultaneously shuts off the positive output voltage and the negative output voltage.

2. The output circuit according to claim 1, characterized in that: The voltage divider circuit includes a first resistor and a second resistor. After the first resistor and the second resistor are connected in series, one end is one end of the voltage divider circuit, the other end is the other end of the voltage divider circuit, and the middle connection point is the voltage divider point of the voltage divider circuit.

3. The output circuit according to claim 1, characterized in that: The voltage divider circuit includes a resistor and a Zener diode, wherein the cathode of the resistor and the Zener diode connected in series is one end of the voltage divider circuit, the anode is the other end of the voltage divider circuit, and the middle connection point is the voltage divider point of the voltage divider circuit.

4. The output circuit according to claim 1, characterized in that: The short-circuit protection trigger circuit includes a first switch tube, a second switch tube and a resistor, one end of the first switch tube is connected to the first end of the short-circuit protection trigger circuit, the other end of the first switch tube and one end of the second switch tube are simultaneously connected to the fourth end of the short-circuit protection trigger circuit, the other end of the second switch tube is connected to the second end of the short-circuit protection trigger circuit, the control end of the first switch tube and the control end of the second switch tube are simultaneously connected to the third end of the short-circuit protection trigger circuit, and the resistor is connected between one end and the other end of the first switch tube.

5. The output circuit according to claim 4, characterized in that: The other end of the second switch tube is connected to the second end of the short-circuit protection trigger circuit through a resistor, a Zener diode or a 431 device.

6. The output circuit according to any one of claims 4 to 5, characterized in that: The first switch tube is an NPN transistor or an N-channel MOS tube; The second switch tube is a PNP transistor or a P-channel MOS tube; For the first switch tube: when it is an NPN transistor, the collector of the NPN transistor is one end, the emitter is the other end, and the base is the control end; when it is an N-channel MOS transistor, the drain of the N-channel MOS transistor is one end, the source is the other end, and the gate is the control end; For the second switch tube: when it is a PNP transistor, the emitter of the PNP transistor is one end, the collector is the other end, and the base is the control end; when it is a P-channel MOS tube, the source of the P-channel MOS tube is one end, the drain is the other end, and the gate is the control end.

7. The output circuit according to any one of claims 4 to 5, characterized in that: The first switch tube is an NPN transistor or an N-channel MOS tube; The second switch tube is an NPN transistor or an N-channel MOS tube; For the first switch tube: when it is an NPN transistor, the collector of the NPN transistor is one end, the emitter is the other end, and the base is the control end; when it is an N-channel MOS transistor, the drain of the N-channel MOS transistor is one end, the source is the other end, and the gate is the control end; For the second switching tube: when it is an NPN transistor, the collector of the NPN transistor is one end, the emitter is the other end, and the base is the control end; when it is an N-channel MOS tube, the drain of the N-channel MOS tube is one end, the source is the other end, and the gate is the control end.

8. The output circuit according to any one of claims 4 to 5, characterized in that: The first switch tube is a PNP transistor or a P-channel MOS tube; The second switch tube is an NPN transistor or an N-channel MOS tube; For the first switch tube: when it is a PNP transistor, the emitter of the PNP transistor is one end, the collector is the other end, and the base is the control end; when it is a P-channel MOS transistor, the source of the P-channel MOS transistor is one end, the drain is the other end, and the gate is the control end; For the second switching tube: when it is an NPN transistor, the collector of the NPN transistor is one end, the emitter is the other end, and the base is the control end; when it is an N-channel MOS tube, the drain of the N-channel MOS tube is one end, the source is the other end, and the gate is the control end.

9. The output circuit according to any one of claims 4 to 5, characterized in that: The first switch tube is a PNP transistor or a P-channel MOS tube; The second switch tube is a PNP transistor or a P-channel MOS tube; For the first switch tube: when it is a PNP transistor, the emitter of the PNP transistor is one end, the collector is the other end, and the base is the control end; when it is a P-channel MOS transistor, the source of the P-channel MOS transistor is one end, the drain is the other end, and the gate is the control end; For the second switch tube: when it is a PNP transistor, the emitter of the PNP transistor is one end, the collector is the other end, and the base is the control end; when it is a P-channel MOS tube, the source of the P-channel MOS tube is one end, the drain is the other end, and the gate is the control end.

10. A switching power supply, comprising a positive DC voltage bus, a negative DC voltage bus, a positive voltage output point, an intermediate voltage output point, a negative voltage output point and a short-circuit protection circuit, wherein one end of the short-circuit protection circuit is simultaneously connected to the positive DC voltage bus and the positive voltage output point of the switching power supply, and the other end is simultaneously connected to the negative DC voltage bus and the negative voltage output point of the switching power supply, characterized in that: The switching power supply further comprises the output circuit according to any one of claims 1 to 9.

11. The switching power supply according to claim 10, characterized in that: The DC power supply of the positive DC voltage bus and the negative DC voltage bus comes from a transformer rectified output.

Images