An output circuit and switching power supply

Abstract

This invention discloses an output circuit and a switching power supply. The output circuit includes: a voltage divider circuit, one end of which is connected to a positive DC voltage bus, and the other end of which is connected to a negative DC voltage bus; and a short-circuit protection trigger circuit, with a first end connected to one end of the voltage divider circuit, a second end connected to the other end of the voltage divider circuit, a third end connected to the voltage divider point of the voltage divider circuit, and a fourth end connected to the intermediate voltage output point of the switching power supply. When the switching power supply is operating normally, a positive voltage to the intermediate voltage output point generates a positive output voltage through the voltage divider circuit and the short-circuit protection trigger circuit, and a negative voltage to the intermediate voltage output point generates a negative output voltage through the same circuit. When a short circuit occurs between the intermediate voltage output point and the positive voltage output point, or between the intermediate voltage output point and the negative voltage output point, the short-circuit protection trigger circuit activates, simultaneously shutting off both the positive and negative output voltages. This invention is beneficial for protecting the driven semiconductors in the downstream circuit.

Description

Technical Field

[0001] This invention relates to the field of power supply circuit technology, and in particular to an output circuit and a switching power supply. Background Technology

[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 on or off. In these cases, the power supply will provide positive (+V), neutral (0V), and negative (-V) voltages, which is achieved by grounding the intermediate voltage supply.

[0004] A known adjustable three-output circuit provides a precise voltage drop between the intermediate output point and either the positive or negative output point by inserting a Zener diode between the appropriate output voltages. 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 their midpoint serving as the intermediate output voltage. Figure 1 and Figure 2 An example of this three-output DC voltage supply is provided.

[0005] However, when a short circuit occurs across the resistors of the voltage divider, the total voltage will be applied across the Zener diode, causing it to break down and resulting in a large current flowing through it. Even if the DC power supply itself has short-circuit protection, the current may not be sufficient to trigger the power supply's short-circuit protection, and the Zener diode may still be damaged due to overvoltage, overcurrent, overheating, etc.

[0006] To address the aforementioned problems, Chinese Invention Patent 202180084821.6 provides a solution, as shown in the appendix. Figure 3 By replacing the Zener diode with an adjustable output and adding a current-limiting resistor, the current-limiting resistor can limit the current flowing through the adjustable output when a short circuit occurs across the resistor in the voltage divider, thus protecting the adjustable output. However, this introduces other problems: when the intermediate voltage output point is short-circuited with the positive or negative voltage output point, the negative or positive voltage output will equal the input power. In this case, when the circuit is applied to the gate drive circuit, the driver output voltage will follow this voltage, which may damage the transistor because it exceeds the voltage range of the transistor gate.

[0007] Similarly, Chinese invention patent 202211107137.8 also provides a solution to prevent the voltage regulator from being damaged due to exceeding the device's power dissipation capacity, as shown in the appendix. Figure 4 When the intermediate voltage point is short-circuited with the positive or negative output voltage point, one of the transistors in the bistable latch circuit will turn off, thus protecting the other transistor. However, it has the same problem as the solution provided in Chinese Invention Patent 202180084821.6: when the intermediate voltage output point is short-circuited with the positive or negative voltage output point, the negative 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 damage the transistor because it exceeds the voltage range of the transistor gate. Summary of the Invention

[0008] 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 that can convert a single power supply with short-circuit protection into a dual power supply with adjustable positive and negative outputs. When a short circuit occurs at the intermediate point, the short-circuit protection of the power supply can be triggered. If a short circuit occurs in either path, the other output will also be shut down simultaneously to protect the driven semiconductors at the back end.

[0009] As a first aspect of the present invention, the provided embodiment of the output circuit is as follows:

[0010] An output circuit is applied to a switching power supply, the switching power supply including 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. The output circuit includes:

[0011] The voltage divider circuit has one end connected to the positive DC voltage bus and the other end connected to the negative DC voltage bus.

[0012] The short-circuit protection trigger circuit has a first terminal connected to one end of the voltage divider circuit, a second terminal connected to the other end of the voltage divider circuit, a third terminal connected to the voltage divider point of the voltage divider circuit, and a fourth terminal used to connect to the intermediate voltage output point of the switching power supply.

[0013] When the switching power supply is working normally, the positive voltage output point to the intermediate voltage output point of the switching power supply generates a positive output voltage through the voltage divider circuit and the short-circuit protection trigger circuit, and the negative voltage output point to the intermediate voltage output point of the switching power supply generates a negative output voltage through the voltage divider circuit and the short-circuit protection trigger circuit.

[0014] When the intermediate voltage output point of the switching power supply is short-circuited to the positive voltage output point or short-circuited to the negative voltage output point, the short-circuit protection trigger circuit is activated, and the positive output voltage and the negative output voltage are simultaneously shut off.

[0015] Preferably, the voltage divider circuit includes a first resistor and a second resistor, wherein one end of the first resistor and the second resistor are connected in series, the other end is the other end of the voltage divider circuit, and the intermediate connection point is the voltage dividing point of the voltage divider circuit.

[0016] Preferably, the voltage divider circuit includes a resistor and a Zener diode, wherein the cathode of the series connection between the resistor and the Zener diode is one end of the voltage divider circuit, the anode is the other end of the voltage divider circuit, and the intermediate connection point is the voltage dividing point of the voltage divider circuit.

[0017] Preferably, the short-circuit protection trigger circuit includes a first switch, a second switch, and a resistor. One end of the first switch is connected to a first terminal of the short-circuit protection trigger circuit, and the other end of the first switch and one end of the second switch are simultaneously connected to a fourth terminal of the short-circuit protection trigger circuit. The other end of the second switch is connected to a second terminal of the short-circuit protection trigger circuit, and the control terminals of the first and second switches are simultaneously connected to a third terminal of the short-circuit protection trigger circuit. The resistor is connected between one end and the other end of the first switch.

[0018] Furthermore, the other end of the second switch is connected to the second terminal of the short-circuit protection trigger circuit via a resistor, a Zener diode, or a TL431.

[0019] Preferably, the first switching transistor is an NPN transistor or an N-channel MOSFET;

[0020] The second switching transistor is a PNP transistor or a P-channel MOSFET;

[0021] For the first switching transistor: 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 terminal; when it is an N-channel MOSFET, the drain of the N-channel MOSFET is one end, the source is the other end, and the gate is the control terminal.

[0022] For the second switching transistor: when it is a PNP transistor, the emitter is one end, the collector is the other end, and the base is the control terminal; when it is a P-channel MOSFET, the source is one end, the drain is the other end, and the gate is the control terminal.

[0023] Preferably, the first switching transistor is an NPN transistor or an N-channel MOSFET;

[0024] The second switching transistor is an NPN transistor or an N-channel MOSFET;

[0025] For the first switching transistor: 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 terminal; when it is an N-channel MOSFET, the drain of the N-channel MOSFET is one end, the source is the other end, and the gate is the control terminal.

[0026] For the second switching transistor: 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 terminal; when it is an N-channel MOSFET, the drain of the N-channel MOSFET is one end, the source is the other end, and the gate is the control terminal.

[0027] Preferably, the first switching transistor is a PNP transistor or a P-channel MOSFET;

[0028] The second switching transistor is an NPN transistor or an N-channel MOSFET;

[0029] For the first switching transistor: when it is a PNP transistor, the emitter is one end, the collector is the other end, and the base is the control terminal; when it is a P-channel MOSFET, the source is one end, the drain is the other end, and the gate is the control terminal.

[0030] For the second switching transistor: 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 terminal; when it is an N-channel MOSFET, the drain of the N-channel MOSFET is one end, the source is the other end, and the gate is the control terminal.

[0031] Preferably, the first switching transistor is a PNP transistor or a P-channel MOSFET;

[0032] The second switching transistor is a PNP transistor or a P-channel MOSFET;

[0033] For the first switching transistor: when it is a PNP transistor, the emitter is one end, the collector is the other end, and the base is the control terminal; when it is a P-channel MOSFET, the source is one end, the drain is the other end, and the gate is the control terminal.

[0034] For the second switching transistor: when it is a PNP transistor, the emitter is one end, the collector is the other end, and the base is the control terminal; when it is a P-channel MOSFET, the source is one end, the drain is the other end, and the gate is the control terminal.

[0035] As a second aspect of the present invention, the technical solution of the provided switching power supply embodiment is as follows:

[0036] A 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. 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 switching power supply further includes the output circuit described in any of the first aspects above.

[0037] Preferably, the DC power supply for the positive DC voltage bus and the negative DC voltage bus comes from the rectified output of the transformer.

[0038] The specific working principle of this invention will be analyzed and explained in specific embodiments, and will not be repeated here. Compared with the prior art, the beneficial effects of this invention are as follows:

[0039] A short-circuit protection trigger circuit has been added. When a short circuit occurs between the intermediate voltage output point and the positive voltage output point or between the intermediate voltage output point and the negative voltage output point of the switching power supply, the short-circuit protection trigger circuit is activated, simultaneously shutting down the positive and negative output voltages. This allows the power supply to be converted from a single-channel power supply with short-circuit protection to a dual-power supply with adjustable positive and negative outputs. When a short circuit occurs at the intermediate point, the power supply's short-circuit protection can be triggered, and if either channel short-circuits, the other output will also shut down synchronously. When used as a gate driver power supply circuit, it can protect the driven semiconductor devices when the power supply is short-circuited. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of a three-output power supply circuit in the existing technology.

[0041] Figure 2 This is a schematic diagram of a three-output power supply circuit in the existing technology.

[0042] Figure 3 The circuit schematic diagram is shown in the embodiment of Chinese invention patent 202211107137.8;

[0043] Figure 4 The circuit schematic diagram is shown in the embodiment of Chinese invention patent 202180084821.6;

[0044] Figure 5 This is a circuit schematic diagram of the first embodiment of the present invention;

[0045] Figure 6 This is a circuit schematic diagram of the second embodiment of the present invention;

[0046] Figure 7 This is a circuit schematic diagram of the third embodiment of the present invention;

[0047] Figure 8 This is a circuit schematic diagram of the fourth embodiment of the present invention;

[0048] Figure 9 This is a circuit schematic diagram of the fifth embodiment of the present invention;

[0049] Figure 10 This is a circuit schematic diagram of the sixth embodiment of the present invention;

[0050] Figure 11 This is a circuit schematic diagram of the seventh embodiment of the present invention. Detailed Implementation

[0051] This invention proposes 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. One end of the short-circuit protection circuit is connected to both the positive DC voltage bus and the positive voltage output point of the switching power supply, and the other end is connected to both 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 connected to the positive DC voltage bus, and the other end of which is connected to the negative DC voltage bus; a short-circuit protection trigger circuit, the first end of which is connected to one end of the voltage divider circuit, the second end of which is connected to the other end of the voltage divider circuit, the third end of which is connected to the voltage divider point of the voltage divider circuit, and the fourth end of which is connected to the intermediate voltage output point of the switching power supply; when the switching power supply is working normally, the positive voltage output point to the intermediate voltage output point generates a positive output voltage through the voltage divider circuit and the short-circuit protection trigger circuit, and the negative voltage output point to the intermediate voltage output point generates a negative output voltage 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 or between the intermediate voltage output point and the negative voltage output point, the short-circuit protection trigger circuit is triggered to work, and the positive and negative output voltages are turned off simultaneously.

[0052] This invention enables the conversion from a single power supply with short-circuit protection to a dual power supply with adjustable positive and negative outputs. When a short circuit occurs at the intermediate point, the short-circuit protection of the power supply can be triggered, and if a short circuit occurs in either power supply, the output of the other power supply will also be shut down simultaneously.

[0053] It should be noted that the terms "comprising" and "having" and any variations thereof described in the specification and claims of this application are intended to cover non-exclusive inclusion. For example, including a series of components, unit circuits or control timings is not necessarily limited to those components, unit circuits or control timings that are explicitly listed, but may include components, unit circuits or control timings that are not explicitly listed or that are inherent to these circuits.

[0054] Furthermore, unless otherwise specified, the embodiments and features described in this application may be combined with each other.

[0055] It should be understood that, in the specification and claims, when an element is described as being "connected" to another element, that element may be "directly connected" to that other element or "connected" to that other element through a third element; when a step is described as being connected to another step, that step may be connected directly to that other step or connected to that other step through a third step.

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Circuits derived from simple combinations of the features of the different embodiments described below also fall within the core concept of this invention.

[0057] First Embodiment

[0058] This embodiment provides one output voltage; see [link to previous section]. Figure 5 The circuit schematic diagram of the first embodiment of the present invention is shown below, and the circuit modules and connections are described as follows:

[0059] A positive DC voltage bus (DC+) and a negative DC voltage bus (DC-) are used to connect to a DC power supply with short-circuit protection. The output ports are: positive voltage output point Vo+, negative voltage output point Vo-, and intermediate voltage output point 0V. An adjustable voltage divider circuit is connected between the positive DC voltage bus (DC+) and the negative DC voltage bus (DC-). This adjustable voltage divider circuit includes a positive voltage divider and a negative voltage divider. In this embodiment, both the positive and negative voltage dividers use resistive devices, and their cathodes are connected together. A short-circuit protection trigger circuit is connected between the positive DC voltage bus (DC+) and the negative DC voltage bus (DC-). This short-circuit protection trigger circuit includes a first transistor Q101, a second transistor Q102, and a resistor R102. The first transistor is an NPN transistor or an N-channel transistor. The first transistor is an NPN transistor (the diagram and the connection below only use an NPN transistor as an example), and the second transistor is a PNP transistor or a P-channel MOSFET (the diagram and the connection below only use a PNP transistor as an example). The bases of the two transistors are connected and connected to the midpoint of the connection between the positive and negative voltage dividers. The collector of the first transistor is connected to the positive DC voltage bus and serves as the positive voltage output point. The emitter of the first transistor is connected to the emitter of the second transistor and serves as the intermediate voltage output point. The collector of the second transistor is connected to the negative DC bus and serves as the negative voltage output point. The two ends of the resistor R102 are connected to the collector and emitter of the first transistor, respectively. 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.

[0060] The DC power supply mentioned in the above circuits includes any power supply with short-circuit protection, DC-DC converter output, AC-DC converter output, transformer rectifier output, etc.

[0061] The working principle of this embodiment is described as follows:

[0062] (1) Adjustable voltage divider circuit:

[0063] This circuit is mainly used to set positive and negative output voltages. Resistors R101 and R103 in the circuit act as voltage dividers. 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. Adjusting the voltage divider resistors can set different positive and negative voltage outputs. At the same time, appropriately increasing the resistance value of the voltage divider resistors can reduce power consumption.

[0064] (2) Short-circuit protection trigger circuit:

[0065] This circuit is mainly used to generate positive and negative output voltages in conjunction with an adjustable voltage divider circuit during normal operation. Furthermore, when a short circuit occurs between the intermediate output voltage point and either the positive or negative output voltage point, it triggers the DC power supply's short-circuit protection and simultaneously shuts down the other output. A detailed analysis follows:

[0066] When the circuit is in normal operating condition, let the DC power supply voltage (i.e., the voltage between the positive DC voltage bus DC+ and 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- If the resistance values ​​of each voltage divider are directly represented by their corresponding symbols in the attached diagram, then the voltage at the midpoint between the first and second voltage dividers, V1 = V... DC R103 / (R101+R103), since the base voltage of the second transistor Q102 is V1, if the second transistor Q102 is not conducting, the voltage across resistor R102 will be 0 because no current flows through it. Therefore, the emitter voltage of the second transistor Q102 will be the voltage of the positive DC voltage bus DC+. Thus, the base voltage of the second transistor Q102 is lower than its emitter voltage. By adjusting the resistance values ​​of the first and second voltage dividers, the voltage difference between the emitter and collector of the second transistor Q102 (i.e., the voltage of the positive DC voltage bus DC+ - V1) can be made greater than its turn-on threshold V. EB2 (Generally 0.3V to 0.7V, depending on the characteristics of the second transistor itself), therefore, 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 common emitter, and the polarities of the first transistor Q101 and the second transistor Q102 are opposite, it can be known that the first transistor is in the off state. Therefore, V O+ =V DC -(V1+V EB2 V O- =-(V1+V EB2 It is worth noting that this circuit is used in a transistor drive power supply circuit, where the voltage V between the positive output point and the intermediate output point is... O+ The voltage is typically set between 15 and 20V, with the negative output point voltage relative to the intermediate output point V. O- It is generally set between -3V and -9V, depending on V. O+ =V DC -(V1+V EB2 ) and V O- =-(V1+V EB2As can be seen, 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 voltage V between the base and collector of the second transistor Q102 is... BC =V1>0, meaning the base voltage of the second transistor Q102 is higher than the collector voltage, indicating that the second transistor Q102 is operating in the amplification region. At this time, the V of the second transistor Q102 is... EB It is susceptible to the influence of the emitter-collector current flowing through the second transistor Q102, resulting in V O+ V O+ The output voltage is unstable; see the seventh embodiment for an improved example.

[0067] When a short circuit occurs between the intermediate voltage output point and the positive voltage output point (i.e., V... O+ When the voltage is 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. The base voltage of the second transistor Q102 is lower than the emitter voltage, so it 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- is... DC =0V, and since V O+ =V DC -(V1+V EB =0V, therefore V O- =-(V1+V EB The voltage is 0V, thus ensuring that when a short circuit occurs between the intermediate voltage output point and the positive voltage output point, V... O- =0V,V O+ =0V, meaning that a short circuit occurs in this path, and the other path will also be turned off simultaneously. Moreover, when a short circuit occurs between the intermediate voltage output point and the positive voltage output point, the emitter and collector of the second transistor Q102 are essentially directly connected across the positive and negative buses of the DC power supply. At this time, the current can be limited at the base of the second transistor by resistor R101 to prevent the current flowing through the emitter to the collector of the second transistor from exceeding the rated current of the second transistor and causing damage.

[0068] When a short circuit occurs between the intermediate voltage output point and the negative voltage output point (i.e., V... O-When V1 = 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, thus turning off the PNP second transistor Q102. 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 and second voltage dividers, and simultaneously ensuring that the voltage difference between the base and emitter of the first transistor Q101 (i.e., V1 - the voltage of the negative DC voltage bus DC-) is greater than its turn-on threshold V1, the voltage of the second transistor Q102 is turned off. EB1 (Typically 0.3V to 0.7V, depending on the characteristics of the second transistor itself). At this time, the first NPN transistor Q101 is turned on. 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, i.e., V. DC =0V, and since V O- =0V, therefore V O+ =V DC -(V1+V EB2 )=0V, thus achieving V when a short circuit occurs between the intermediate voltage output point and the negative voltage output point. O- =0V,V O+ =0V, meaning that a short circuit occurs in this path, and the other path will also be turned off simultaneously. 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 essentially directly connected across the positive and negative buses of the DC power supply. At this time, the current at the base of the first transistor Q101 can be limited by the resistor R101 to prevent the current flowing through the emitter to collector of the first transistor Q101 from exceeding the rated current of the first transistor Q101 and causing damage.

[0069] Please continue reading Figure 5 A resistor R102 is connected in parallel between the collector and emitter of the first transistor Q101. In this embodiment and the following embodiments, the resistor R102 mainly serves as a pull-up resistor to prevent the emitter / collector of the first transistor and the second transistor from floating to ground, which would cause the first transistor and the second transistor to be unable to reliably turn off or turn on under the above operating conditions. In addition, it also prevents the intermediate output point from floating to ground, which would cause the output to be unstable.

[0070] Second Embodiment

[0071] This embodiment provides one output voltage; see [link to previous section]. Figure 6 This 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 transistor or an N-channel MOSFET, and the second transistor Q102 is an NPN transistor or an N-channel MOSFET. Figure 6The collector of the first transistor is connected to the positive DC voltage bus and serves as the positive voltage output point. The emitter of the first transistor is connected to the collector of the second transistor and serves as the intermediate voltage output point. The emitter of the second transistor is connected to the negative DC bus and serves as the negative voltage output point.

[0072] Figure 6 and Figure 5 The difference lies in the polarity of the second transistor Q102, and the emitter of the second transistor Q102 is connected to the negative DC voltage bus DC-. By analyzing the voltage state between the base and emitter of the first transistor Q101 and the second transistor Q102 under different states, it can be seen that when the circuit is in normal working state, and when a short circuit occurs between the intermediate voltage output point and the positive voltage output point, the second transistor Q102 is turned on and the first transistor Q101 is turned off. When a short circuit occurs between the intermediate voltage output point and the negative voltage output point, the second transistor Q102 is turned off and the first transistor Q101 is turned on, thus achieving the same purpose of the invention.

[0073] Third Embodiment

[0074] This embodiment provides one output voltage; see [link to previous section]. Figure 7 The circuit diagram of the third embodiment of the present invention differs from the first and second embodiments in 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.

[0075] Figure 6 and Figure 5 The difference lies in the reversal of the polarities of the first transistor Q101 and the second transistor Q102, and the first transistor Q101 and the second transistor Q102 are changed to common collector electrodes. By analyzing the base-emitter voltage state of the first transistor Q101 and the second transistor Q102 under different states, it can be obtained that when the circuit is in normal working state, and when a short circuit occurs between the intermediate voltage output point and the positive voltage output point, the second transistor Q102 is turned on and the first transistor Q101 is turned off; when a short circuit occurs between the intermediate voltage output point and the negative voltage output point, the second transistor Q102 is turned off and the first transistor Q101 is turned on, thus achieving the same purpose of the invention.

[0076] Fourth embodiment

[0077] This embodiment provides one output voltage; see [link to previous section]. 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.

[0078] Figure 8 and Figure 5 The difference lies in the polarity of the first transistor Q101, and the emitter of the first transistor Q101 is connected to the positive DC voltage bus DC+. By analyzing the voltage state between the base and emitter of the first transistor Q101 and the second transistor Q102 under different states, it can be seen that when the circuit is in normal working state, and when a short circuit occurs between the intermediate voltage output point and the positive voltage output point, the second transistor Q102 is turned on and the first transistor Q101 is turned off. When a short circuit occurs between the intermediate voltage output point and the negative voltage output point, the second transistor Q102 is turned off and the first transistor Q101 is turned on, thus achieving the same purpose of the invention.

[0079] Fifth Embodiment

[0080] This embodiment provides one output voltage; see [link to previous section]. Figure 9 This is a circuit schematic 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 changed from resistor R103 to Zener diode D101.

[0081] In this embodiment, the voltage from the positive voltage output point to the intermediate voltage output point is equal to the voltage across 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 Zener diode D101 plus the voltage drop V from the emitter to the base of the second transistor. eb Since the voltage across a Zener diode can remain almost constant 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.

[0082] 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 precise. This embodiment is also applicable to the second, third, and fourth embodiments.

[0083] Sixth Embodiment

[0084] This embodiment provides one output voltage; see [link to previous section]. Figure 10This is a circuit schematic 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 changed from resistor R101 to Zener diode D101.

[0085] 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 resistor R103 plus the voltage drop V from the emitter to the base of the second transistor. eb Since the voltage across a Zener diode can remain almost constant 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.

[0086] 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 precise. This embodiment is also applicable to the second, third, and fourth embodiments.

[0087] Seventh Embodiment

[0088] This embodiment provides one output voltage; see [link to previous section]. Figure 11 This is a circuit schematic diagram of the sixth embodiment of the present invention. This embodiment is an improvement on the first embodiment. The difference between the first embodiment and the first embodiment is that the collector of the second transistor is connected to the negative DC voltage bus through a series resistor R104.

[0089] As can be seen from the analysis of the first embodiment, when there is no short circuit at the intermediate output voltage point, the circuit is in normal working condition. The first transistor is in the off state, and the second transistor is in the on state and operates in the amplification region. Since the second transistor operates in the amplification region, the voltage drop V from the emitter to the base of the second transistor is... eb It is susceptible to the current I flowing from the emitter to the collector of the second transistor. ec The influence of I causes 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 voltage output point, to be affected. ec The impact.

[0090] To address the aforementioned issues, connecting the collector of the second transistor to a negative DC voltage bus via a series resistor R104 increases the collector voltage, making it greater than the base voltage and the emitter voltage greater than the base voltage. This allows the second transistor to operate in the saturation region and reduces the emitter-to-collector current I. ec The effect on the output voltage. This embodiment also applies to the second, third, fourth, fifth, and sixth embodiments, and resistor R104 can be replaced with a Zener diode or TL431 to achieve the same purpose.

[0091] Eighth embodiment

[0092] This 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 connected to both the positive DC voltage bus and the positive voltage output point of the switching power supply, and the other end is connected to both the negative DC voltage bus and the negative voltage output point of the switching power supply. The switching power supply also includes any one of the output circuits in the first to seventh embodiments.

[0093] The switching power supply in this embodiment includes any one of the output circuits in the first to seventh embodiments, which realizes the conversion from a single power supply with short-circuit protection to a dual power supply with adjustable positive and negative outputs. When a short circuit occurs at the intermediate point, the short-circuit protection of the power supply can be triggered, and if a short circuit occurs in any one of the outputs, the other output will also be shut down simultaneously.

[0094] 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 this circuit is used to power a power transistor (not shown), it can provide a large transient gate drive current. When this circuit is not used to drive a power transistor, the first and second capacitors can be omitted. The DC power supply for the positive DC voltage bus and the negative DC voltage bus can come from the rectified output of the transformer. The intermediate voltage can be 0V.

[0095] The above are merely embodiments of the present invention. It should be particularly noted that the above embodiments should not be regarded as limitations on the present invention. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. An output circuit applied to a switching power supply, the switching power supply including 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 output circuit includes: The voltage divider circuit has one end connected to the positive DC voltage bus and the other end connected to the negative DC voltage bus. The short-circuit protection trigger circuit has a first terminal connected to one end of the voltage divider circuit, a second terminal connected to the other end of the voltage divider circuit, a third terminal connected to the voltage divider point of the voltage divider circuit, and a fourth terminal used to connect to the intermediate voltage output point of the switching power supply. When the switching power supply is working normally, the positive voltage output point to the intermediate voltage output point of the switching power supply generates a positive output voltage through the voltage divider circuit and the short-circuit protection trigger circuit, and the negative voltage output point to the intermediate voltage output point of the switching power supply generates a negative output voltage through the voltage divider circuit and the short-circuit protection trigger circuit. When the intermediate voltage output point of the switching power supply is short-circuited to the positive voltage output point or short-circuited to the negative voltage output point, the short-circuit protection trigger circuit is triggered to work, and the positive output voltage and the negative output voltage are turned off at the same time. The short-circuit protection trigger circuit includes a first switch, a second switch, and a resistor. One end of the first switch is connected to a first terminal of the short-circuit protection trigger circuit. The other end of the first switch and one end of the second switch are simultaneously connected to a fourth terminal of the short-circuit protection trigger circuit. The other end of the second switch is connected to a second terminal of the short-circuit protection trigger circuit. The control terminals of the first switch and the second switch are simultaneously connected to a third terminal of the short-circuit protection trigger circuit. The resistor is connected between one end and the other end of the first switch.

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

4. The output circuit according to claim 1, characterized in that: The other end of the second switch is connected to the second terminal of the short-circuit protection trigger circuit through a resistor, a Zener diode, or a TL431.

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

6. The output circuit according to claim 4, characterized in that: The first switching transistor is an NPN transistor or an N-channel MOSFET; The second switching transistor is an NPN transistor or an N-channel MOSFET; For the first switching transistor: 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 terminal; when it is an N-channel MOSFET, the drain of the N-channel MOSFET is one end, the source is the other end, and the gate is the control terminal. For the second switching transistor: 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 terminal; when it is an N-channel MOSFET, the drain of the N-channel MOSFET is one end, the source is the other end, and the gate is the control terminal.

7. The output circuit according to claim 4, characterized in that: The first switching transistor is a PNP transistor or a P-channel MOSFET; The second switching transistor is an NPN transistor or an N-channel MOSFET; For the first switching transistor: when it is a PNP transistor, the emitter is one end, the collector is the other end, and the base is the control terminal; when it is a P-channel MOSFET, the source is one end, the drain is the other end, and the gate is the control terminal. For the second switching transistor: 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 terminal; when it is an N-channel MOSFET, the drain of the N-channel MOSFET is one end, the source is the other end, and the gate is the control terminal.

8. The output circuit according to claim 4, characterized in that: The first switching transistor is a PNP transistor or a P-channel MOSFET; The second switching transistor is a PNP transistor or a P-channel MOSFET; For the first switching transistor: when it is a PNP transistor, the emitter is one end, the collector is the other end, and the base is the control terminal; when it is a P-channel MOSFET, the source is one end, the drain is the other end, and the gate is the control terminal. For the second switching transistor: when it is a PNP transistor, the emitter is one end, the collector is the other end, and the base is the control terminal; when it is a P-channel MOSFET, the source is one end, the drain is the other end, and the gate is the control terminal.

9. 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 includes the output circuit described in any one of claims 1 to 8.

10. The switching power supply according to claim 9, characterized in that: The DC power supply for the positive DC voltage bus and the negative DC voltage bus comes from the rectified output of the transformer.

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