Switching power supply with output overvoltage protection and reverse connection prevention functions

Abstract

The utility model provides a switching power supply with output overvoltage protection and reverse connection prevention functions, which is characterized in that a group of output reverse connection prevention overvoltage protection circuits consisting of a triode, a first MOS (Metal Oxide Semiconductor) tube, a second MOS tube, a third MOS tube, a voltage-regulator tube, a first resistor, a second resistor, a third resistor, a fourth resistor and a fifth resistor are introduced into the output end of a secondary side, when the output voltage of the switching power supply is too high, the voltage-regulator tube is switched on, and the first resistor, the second resistor, the third resistor and the fifth resistor are switched on; therefore, the base voltage of the triode is lowered, the triode is conducted, the first MOS tube is switched off, the output loop is switched off, the output abnormal high voltage does not affect the battery at the load end, and the potential safety hazard at the load end is avoided. When the positive electrode and the negative electrode of the load wiring of the switching power supply are reversely connected, the positive electrode voltage of the output terminal is lower than the negative electrode voltage at the moment, the grid electrode voltage of the second MOS tube and the grid electrode voltage of the third MOS tube are lower than the source electrode voltage, the second MOS tube and the third MOS tube are turned off, reverse voltage cannot enter the switching power supply, and the switching power supply is effectively prevented from being damaged due to reverse voltage impact.

Description

Technical Field

[0001] This utility model relates to the field of power supply technology, and in particular to a switching power supply with overvoltage protection and reverse connection protection. Background Technology

[0002] The conventional overvoltage protection function of switching power supplies mainly works by the power control chip detecting the voltage coupled from the secondary output side to the primary auxiliary winding via the transformer. When the secondary output voltage rises abnormally, the primary auxiliary winding voltage also rises. The voltage management chip determines whether the product has malfunctioned by judging the magnitude of the primary auxiliary winding voltage increase and promptly enters overvoltage protection mode to cut off the output. Reverse connection protection is generally implemented by inserting a diode in series in the output circuit. Furthermore, reverse connection protection and overvoltage protection functions are controlled by different modules.

[0003] The aforementioned switching power supply achieves control by detecting changes in the electrical signal through transformer coupling. This results in significant differences in the detected signal changes under load and no-load conditions, making it impossible to accurately implement overvoltage protection control. Generally, the power management chip can only provide timely and accurate overvoltage protection under load, but it cannot activate protection in time under no-load conditions, causing the output voltage to exceed the protection threshold and exceed the specifications. Furthermore, the reverse connection protection function implemented through series diodes has limitations; it can easily cause excessive losses and affect efficiency under high current conditions. Utility Model Content

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of this utility model is to provide a switching power supply with overvoltage protection and reverse connection protection, which can accurately achieve overvoltage protection under different load conditions and also achieve effective reverse connection protection under high current conditions.

[0005] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0006] A switching power supply with overvoltage protection and reverse connection protection includes a transformer, a primary side circuit, a secondary side circuit, a control circuit, input terminals, and output terminals. The primary side circuit is connected between the input terminals and the primary winding of the transformer. The secondary side circuit is connected between the output terminals and the secondary winding of the transformer. The control circuit is connected to the primary auxiliary winding of the transformer. The secondary side circuit includes a transistor, a first MOSFET, a second MOSFET, a third MOSFET, a Zener diode, a first resistor, a second resistor, a third resistor, a fourth resistor, and a fifth resistor. One end of the first resistor, the emitter of the transistor, one end of the third resistor, and the source of the first MOSFET are all connected to one end of the secondary winding. The anode of the Zener diode and the fourth resistor are also connected. One end of the first resistor, the source of the second MOSFET, and the other end of the secondary winding are all grounded. The other end of the first resistor is connected to the cathode of the Zener diode and one end of the second resistor. The other end of the second resistor is connected to the base of the transistor. The collector of the transistor is connected to one end of the third resistor, the gate of the first MOSFET, and the other end of the fourth resistor. The drain of the first MOSFET is connected to the positive terminal of the output terminal and one end of the fifth resistor. The other end of the fifth resistor is connected to the gate of the second MOSFET and the gate of the third MOSFET. The drain of the second MOSFET is connected to the drain of the third MOSFET. The source of the third MOSFET is connected to the negative terminal of the output terminal. The transistor is PNP type, the first MOSFET is P type, and the second and third MOSFETs are N type.

[0007] Optionally, the primary side circuit includes an EMI filter circuit, a rectifier circuit, and an RCD snubber circuit connected sequentially along the direction of electrical signal transmission.

[0008] Optionally, the EMI filter circuit includes a common-mode inductor and a safety capacitor, with the safety capacitor connected in parallel with the input terminal and the common-mode inductor connected in series between the safety capacitor and the rectifier circuit.

[0009] Optionally, the rectifier circuit includes a rectifier bridge and a first electrolytic capacitor. The input terminal of the rectifier bridge is connected to a common-mode inductor, the positive output terminal of the rectifier bridge is connected to the positive terminal of the first electrolytic capacitor and an RCD snubber circuit, and the negative output terminal of the rectifier bridge and the negative terminal of the first electrolytic capacitor are both grounded.

[0010] Optionally, the RCD snubber circuit includes a sixth resistor, a seventh resistor, an eighth resistor, a first capacitor, and a first diode. The positive output terminal of the rectifier bridge, one end of the sixth resistor, one end of the seventh resistor, and one end of the first capacitor are all connected to one end of the primary winding. The other ends of the sixth resistor, the seventh resistor, and the first capacitor are all connected to the cathode of the first diode via the eighth resistor. The anode of the first diode is connected to the other end of the primary winding and the input terminal of the control circuit.

[0011] Optionally, the control circuit includes a main control chip, a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a fifteenth resistor, a sixteenth resistor, a second electrolytic capacitor, and a second diode. The ninth and tenth resistors are connected in series to the positive output terminal of the rectifier bridge and the power supply terminal of the main control chip. The power supply terminal of the main control chip is connected to one end of the eleventh resistor and the positive terminal of the second electrolytic capacitor. The other end of the eleventh resistor is connected to the cathode of the second diode. The anode of the second diode is connected to one end of the primary auxiliary winding and one end of the twelfth resistor. The other end of the twelfth resistor is connected to one end of the thirteenth resistor, one end of the fourteenth resistor, and one output terminal of the main control chip. The other output terminal of the main control chip is connected to one end of the fifteenth resistor and one end of the sixteenth resistor. The other ends of the primary auxiliary winding, the thirteenth resistor, the fourteenth resistor, the fifteenth resistor, the sixteenth resistor, the negative terminal of the second electrolytic capacitor, and the ground terminal of the main control chip are all grounded.

[0012] The beneficial effects of this utility model are as follows:

[0013] A set of overvoltage protection circuits for reverse connection is introduced at the output terminal of the secondary side. When the output voltage of the switching power supply is too high, the Zener diode is turned on, thereby pulling down the base voltage of the transistor, turning on the transistor, turning off the first MOSFET, and disconnecting the output circuit. The abnormal high voltage of the output will not affect the battery at the load end, thus avoiding safety hazards at the load end.

[0014] When the load wiring of the switching power supply is reversed, the positive voltage of the output terminal is lower than the negative voltage, causing the gate voltage of the second and third MOSFETs to be lower than the source voltage. As a result, the second and third MOSFETs are turned off, and the reverse voltage will not enter the switching power supply. This effectively avoids damage to the switching power supply due to reverse voltage surges and prevents excessive losses due to large currents, which would affect efficiency. Attached Figure Description

[0015] Figure 1 The diagram shown is a schematic diagram of the secondary side circuit of a switching power supply with overvoltage protection and reverse connection protection according to an embodiment of the present invention.

[0016] Figure 2 The diagram shown is a schematic of a switching power supply circuit with overvoltage protection and reverse connection protection in an embodiment of this utility model. Detailed Implementation

[0017] To better understand the technical content, objectives, and effects of this utility model, the following detailed description, in conjunction with specific embodiments and accompanying drawings, is provided. It should be noted that, unless otherwise specified, the embodiments and features of this utility model can be combined with each other. Many specific details are set forth in the following description to provide a thorough understanding of this utility model; the described embodiments are merely a part of, and not all, of the embodiments of this utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without inventive effort are within the scope of protection of this utility model.

[0018] Please refer to Figure 1 and Figure 2 As shown, the embodiment of this utility model is as follows:

[0019] A switching power supply with overvoltage protection and reverse connection protection includes a transformer, a primary side circuit, a secondary side circuit, a control circuit, input terminals, and output terminals. The primary side circuit is connected between the input terminals and the primary winding of the transformer, the secondary side circuit is connected between the output terminals and the secondary winding of the transformer, and the control circuit is connected to the primary auxiliary winding of the transformer. The input terminals are used to connect to an AC power source, and the output terminals are used to connect to a downstream load.

[0020] The primary side circuit includes an EMI filter circuit, a rectifier circuit, and an RCD absorption circuit connected sequentially along the direction of electrical signal transmission.

[0021] The EMI filter circuit includes a common-mode inductor LF1 and a safety capacitor CX1; the rectifier circuit includes a rectifier bridge DB1 and a first electrolytic capacitor EC1; the RCD snubber circuit includes a sixth resistor R4, a seventh resistor R5, an eighth resistor R3, a first capacitor C1, and a first diode D1; and the control circuit includes a main control chip IC1, a ninth resistor R1, a tenth resistor R2, an eleventh resistor R8, a twelfth resistor R11, a thirteenth resistor R9, a fourteenth resistor R10, a fifteenth resistor R6, a sixteenth resistor R7, a second electrolytic capacitor EC3, and a second diode D2.

[0022] One end of the safety capacitor CX1 is connected to the L line of the input terminal, and the other end is connected to the N line of the input terminal, thus forming a parallel connection with the input terminals (L, N). The two input terminals of the common-mode inductor LF1 are respectively connected to the two ends of the safety capacitor CX1, and the two output terminals of the common-mode inductor LF1 are respectively connected to the two input terminals of the rectifier bridge DB1.

[0023] The positive output terminal of rectifier bridge DB1, the positive terminal of the first electrolytic capacitor EC1, one end of the sixth resistor R4, one end of the seventh resistor R5, and one end of the first capacitor C1 are all connected to one end of the primary winding of transformer TR1. The negative output terminal of rectifier bridge DB1 and the negative terminal of the first electrolytic capacitor EC1 are both grounded. The other ends of the sixth resistor R4, the seventh resistor R5, and the first capacitor C1 are all connected to the cathode of the first diode D1 via the eighth resistor R3. The anode of the first diode D1 is connected to the other end of the primary winding and the input terminal of the main control chip IC1.

[0024] The ninth resistor R1 and the tenth resistor R2 are connected in series to the positive output terminal of the rectifier bridge DB1 and the power supply terminal of the main control chip IC1. The power supply terminal of the main control chip IC1 is also connected to one end of the eleventh resistor R8 and the positive terminal of the second electrolytic capacitor EC3. The other end of the eleventh resistor R8 is connected to the cathode of the second diode D2. The anode of the second diode D2 is connected to one end of the primary auxiliary winding Nf1 and one end of the twelfth resistor R11. The other end of the twelfth resistor R11 is connected to one end of the thirteenth resistor R9, one end of the fourteenth resistor R10 and one output terminal of the main control chip IC1. The other output terminal of the main control chip IC1 is connected to one end of the fifteenth resistor R6 and one end of the sixteenth resistor R7. The other ends of the primary auxiliary winding Nf1, the thirteenth resistor R9, the fourteenth resistor R10, the fifteenth resistor R6, the sixteenth resistor R7, the negative terminal of the second electrolytic capacitor EC3 and the ground terminal of the main control chip IC1 are all grounded.

[0025] like Figure 1As shown, the secondary side circuit includes transistor Q2, first MOSFET Q3, second MOSFET Q4, third MOSFET Q5, Zener diode ZD1, first resistor R13, second resistor R14, third resistor R15, fourth resistor R16, and fifth resistor R17. One end of the first resistor R13, the emitter of transistor Q2, one end of the third resistor R15, and the source of the first MOSFET Q3 are all connected to one end of the secondary winding. The anode of Zener diode ZD1, one end of the fourth resistor R16, the source of the second MOSFET Q4, and the other end of the secondary winding are all grounded. The other end of the first resistor R13 is connected to the cathode of Zener diode ZD1 and one end of the second resistor R14. The second resistor R16... The other end of 4 is connected to the base of transistor Q2. The collector of transistor Q2 is connected to one end of the third resistor R15, the gate of the first MOSFET Q3, and the other end of the fourth resistor R16. The drain of the first MOSFET Q3 is connected to the positive output terminal Vout+ and one end of the fifth resistor R17. The other end of the fifth resistor R17 is connected to the gate of the second MOSFET Q4 and the gate of the third MOSFET Q5. The drain of the second MOSFET Q4 is connected to the drain of the third MOSFET Q5. The source of the third MOSFET Q5 is connected to the negative output terminal Vout-. Transistor Q2 is PNP type, first MOSFET Q3 is P type, and second MOSFET Q4 and third MOSFET Q5 are N type.

[0026] It should be noted that the primary side circuit and the secondary side circuit are connected to different grounds.

[0027] One end of the primary winding is a high-level terminal (HV), and the other end of the secondary winding is a low-level terminal (SGND).

[0028] In one specific embodiment, the secondary-side circuit further includes a diode D3, a capacitor C6, a resistor R12, an electrolytic capacitor EC4, and an electrolytic capacitor EC5. One end of the secondary winding is first connected to the forward-biased diode D3 and then to the first resistor R13. The capacitor C6 and the resistor R12 are connected in series and then in parallel with the diode D3. The cathode of the diode D3 is connected to the anodes of both electrolytic capacitors EC4 and EC5. The cathodes of both electrolytic capacitors EC4 and EC5 are grounded. Figure 2 As shown.

[0029] The principle of this embodiment is as follows:

[0030] AC power is input through the input terminal. The common-mode inductor LF1 and the safety capacitor CX1 form an EMI filter circuit, which absorbs the common-mode noise of the power supply and suppresses EMI common-mode signal interference.

[0031] The rectifier bridge DB1 converts 50Hz AC power into DC power, which is then filtered by the large-capacity electrolytic capacitor EC1 to provide a relatively stable DC voltage.

[0032] R3, R4, R5, C1, and D1 form an RCD snubber circuit to absorb the voltage spikes generated by the transformer leakage inductance during the switching of the MOSFET.

[0033] R1, R2, and EC3 form the startup power supply circuit, which provides startup current to the main control IC1, ensuring that the system can start up and work smoothly.

[0034] R6 and R7 form an overcurrent protection circuit. When the output current on the secondary side of the transformer exceeds the limit, the peak current on the primary side will increase proportionally, thereby increasing the current flowing through R6 and R7. When IC1 detects the increased voltage at PIN4 (corresponding to the other output terminal of the main control chip IC1), it can cut off the switching transistor, thus providing protection. The system will only restart and return to normal operation once the voltage at PIN4 returns to normal.

[0035] After IC1 successfully starts up, Nf1, as the feedback winding, together with D2, R8, and EC3, forms a power supply circuit to ensure that the main control IC1 can operate stably and normally.

[0036] Nf1 serves as the feedback winding, forming a main output voltage feedback loop with R9, R10, R11, and PIN3 of IC1 (corresponding to one output terminal of the main control chip IC1) to control the accuracy of the output voltage and ensure that the rated requirements are met at all times.

[0037] The output overvoltage protection circuit, composed of R13, R14, R15, R16, ZD1, Q2, and Q3, activates when a fault occurs in the main output voltage feedback loop, causing the feedback loop to open and the output voltage to become too high. This causes the Zener diode ZD1 to conduct, pulling down the base voltage of transistor Q2 and turning it on. The collector voltage of Q2 then rises. Since the collector of Q2 is connected to the gate of PMOS transistor Q3, the gate voltage of PMOS transistor Q3 rises, causing Q3 to turn off. This disconnects the output circuit, preventing abnormally high voltage from affecting the battery at the load end and effectively avoiding damage to the load end due to high voltage surges.

[0038] R17, Q4, and Q5 form the output reverse connection protection current. When the positive and negative terminals of the load battery of the power supply are reversed, the voltage of the positive terminal of the output terminal is lower than the voltage of the negative terminal, causing the gate voltage of MOSFETs Q4 and Q5 to be lower than the source voltage. As a result, MOSFETs Q4 and Q5 are turned off, and the reverse voltage will not enter the switching power supply, thus protecting the switching power supply circuit from reverse voltage impact.

[0039] The above description is merely an embodiment of the present utility model and does not limit the patent scope of the present utility model. Therefore, any modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present utility model without departing from the technical solution of the present utility model shall still fall within the scope of the technical solution of the present utility model.

Claims

1. A switching power supply with overvoltage protection and reverse connection protection, comprising a transformer, a primary side circuit, a secondary side circuit, a control circuit, input terminals, and output terminals, wherein the primary side circuit is connected between the input terminals and the primary winding of the transformer, the secondary side circuit is connected between the output terminals and the secondary winding of the transformer, and the control circuit is connected to the primary auxiliary winding of the transformer, characterized in that, The secondary side circuit comprises a triode, a first MOS tube, a second MOS tube, a third MOS tube, a stabilizing tube, a first resistor, a second resistor, a third resistor, a fourth resistor and a fifth resistor, one end of the first resistor, an emitter of the triode, one end of the third resistor and a source of the first MOS tube are all connected to one end of the secondary winding, an anode of the stabilizing tube, one end of the fourth resistor, a source of the second MOS tube and the other end of the secondary winding are all grounded, the other end of the first resistor is connected to a cathode of the stabilizing tube and one end of the second resistor, the other end of the second resistor is connected to a base of the triode, a collector of the triode is connected to one end of the third resistor, a gate of the first MOS tube and the other end of the fourth resistor, a drain of the first MOS tube is connected to a positive electrode of an output terminal and one end of the fifth resistor, the other end of the fifth resistor is connected to a gate of the second MOS tube and a gate of the third MOS tube, a drain of the second MOS tube is connected to a drain of the third MOS tube, a source of the third MOS tube is connected to a negative electrode of the output terminal, the triode is PNP type, the first MOS tube is P type, and the second MOS tube and the third MOS tube are N type.

2. The switching power supply of claim 1, wherein The primary side circuit comprises an EMI filter circuit, a rectifier circuit and an RCD absorption circuit connected in sequence along the direction of signal transmission.

3. The switching power supply of claim 2, wherein The EMI filter circuit comprises a common mode inductor and a safety capacitor, the safety capacitor is connected in parallel with the input terminal, and the common mode inductor is connected in series between the safety capacitor and the rectifier circuit.

4. The switching power supply of claim 3, wherein The rectifier circuit comprises a rectifier bridge and a first electrolytic capacitor, an input end of the rectifier bridge is connected to the common mode inductor, a positive electrode output end of the rectifier bridge is connected to a positive electrode of the first electrolytic capacitor and the RCD absorption circuit, and a negative electrode output end of the rectifier bridge and a negative electrode of the first electrolytic capacitor are both grounded.

5. The switching power supply of claim 4, wherein The RCD absorption circuit comprises a sixth resistor, a seventh resistor, an eighth resistor, a first capacitor and a first diode, one end of the positive electrode output end of the rectifier bridge, one end of the sixth resistor, one end of the seventh resistor and one end of the first capacitor are all connected to one end of the primary winding, the other end of the sixth resistor, the other end of the seventh resistor and the other end of the first capacitor are all connected to a cathode of the first diode through the eighth resistor, and an anode of the first diode is connected to the other end of the primary winding and an input end of the control circuit.

6. The switching power supply of claim 5, wherein The control circuit comprises a master control chip, a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a fifteenth resistor, a sixteenth resistor, a second electrolytic capacitor and a second diode, the ninth resistor and the tenth resistor are connected in series between the positive output end of the rectifier bridge and the power supply end of the master control chip, one end of the eleventh resistor and the positive electrode of the second electrolytic capacitor are connected to the power supply end of the master control chip, the other end of the eleventh resistor is connected to the cathode of the second diode, the anode of the second diode is connected to one end of the primary auxiliary winding and one end of the twelfth resistor, the other end of the twelfth resistor is connected to one end of the thirteenth resistor, one end of the fourteenth resistor and one output end of the master control chip, the other output end of the master control chip is connected to one end of the fifteenth resistor and one end of the sixteenth resistor, the other end of the primary auxiliary winding, the other end of the thirteenth resistor, the other end of the fourteenth resistor, the other end of the fifteenth resistor, the other end of the sixteenth resistor, the negative electrode of the second electrolytic capacitor and the ground end of the master control chip are all grounded.

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