A projector switching power supply circuit with protection function

Abstract

This invention relates to the field of switching power supply technology, and provides a projector switching power supply circuit with protection functions, including: a power supply, a power chip, a switching circuit, an auxiliary circuit, a secondary protection circuit, a transformer, an output circuit, and a conversion circuit; pins 3 and 4 of the power chip are respectively connected to the input terminals of the secondary protection circuit, and the power supply circuit is connected to pin 5 of the power chip; the output terminal of the switching circuit is connected to the input terminal of the auxiliary circuit, the output terminal of the auxiliary circuit is connected to the first primary coil of the transformer, and the output terminal of the secondary protection circuit is connected to the second primary coil of the transformer; the first primary coil of the transformer is connected to the input terminal of the output circuit, and the output terminal of the output circuit is used to connect to an external projector; the second secondary coil of the transformer is connected to the input terminal of the conversion circuit, and the output terminal of the conversion circuit is used to output the operating voltage. This invention provides good protection and high reliability.

Description

Technical Field

[0001] This invention relates to the field of switching power supply technology, and specifically to a projector switching power supply circuit with protection functions. Background Technology

[0002] With the rapid development of the digital age, multimedia projectors have entered many venues, providing greater convenience for projection displays and making presentations more convenient and richer. For projector maintenance, preventing circuit malfunctions during operation is crucial, and a suitable switching power supply can ensure the projector's safety and reliability. Modern switching power supplies are widely used in industrial fields due to their high efficiency, high reliability, and small size. When a short circuit occurs on the output side of the switching power supply, a preset protection mechanism needs to be triggered to shut down the power output and protect the downstream load.

[0003] In the projector market for related technologies, switching power supplies are generally used as the power input. These power supplies typically have a series of input / output protections to meet safety requirements. This projector generally uses optocoupler feedback to cut off the voltage at the FB pin of the chip. Since the primary chip cannot detect the feedback voltage, the product cannot output voltage, thus achieving the protection function.

[0004] However, in the above situation, the VCC voltage of the chip will exhibit a sawtooth waveform, entering a continuous cycle of restarts. The power IC chip is actually still working, but in an abnormal operating state, which is unsafe. Therefore, the phenomenon of power supply failure due to MOSFET damage caused by component failure on the transformer secondary side is not uncommon. In particular, when a fault occurs, the temperature rise of the power devices increases, causing the VCC voltage to exhibit a sawtooth waveform when the optocoupler detection feedback cuts off the voltage at the FB pin, continuously restarting and entering an abnormal operating state. When this abnormal operating state occurs, the MOSFET also enters an abnormal operating state, and its temperature rises continuously, eventually leading to a risk of power supply failure and fire, causing significant economic losses and safety hazards to users. Summary of the Invention

[0005] This invention provides a projector switching power supply circuit with protection functions, aiming to solve the problem of poor safety during operation of existing projectors.

[0006] This invention provides a projector switching power supply circuit with protection function, including: a power supply, a power chip, a switching circuit, an auxiliary circuit, a secondary protection circuit, a transformer, an output circuit, and a conversion circuit;

[0007] Pin 1 of the power chip is grounded, and pin 2 of the power chip is used for voltage feedback. Pins 3 and 4 of the power chip are respectively connected to the input terminals of the secondary protection circuit. The power supply circuit is connected to pin 5 of the power chip to supply power to the power chip. Pin 6 of the power chip is connected to the input terminal of the switching circuit. The output terminal of the switching circuit is connected to the input terminal of the auxiliary circuit. The output terminal of the auxiliary circuit is connected to the first primary coil of the transformer. The output terminal of the secondary protection circuit is connected to the second primary coil of the transformer. The first primary coil of the transformer is connected to the input terminal of the output circuit, and the output terminal of the output circuit is used to connect to an external projector. The second primary coil of the transformer is connected to the input terminal of the conversion circuit, and the output terminal of the conversion circuit is used to output the operating voltage.

[0008] The secondary protection circuit includes a first diode, a thermistor, a first resistor, a second resistor, a third resistor, and a first capacitor. The first terminal of the first resistor serves as the first input terminal of the secondary protection circuit, connected to pin 4 of the power chip. The second terminal of the first resistor is connected to the first terminal of the thermistor, and the second terminal of the thermistor is connected to the cathode of the first diode. The anode of the first diode is connected to the first terminal of the second resistor and serves as the output terminal of the secondary protection circuit. The second terminal of the second resistor is connected to the first terminal of the third resistor, and the second terminal of the third resistor is connected to the first terminal of the first capacitor and grounded.

[0009] The second end of the first capacitor is connected to the first end of the third resistor and serves as the second input terminal of the secondary protection circuit, which is used to connect to pin 3 of the power chip.

[0010] Preferably, the switching circuit includes a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a second diode, a second capacitor, a third capacitor, and a MOSFET;

[0011] The first end of the fourth resistor serves as the first input terminal of the switching circuit and is connected to pin 6 of the power chip. The second end of the fourth resistor is connected to the first end of the fifth resistor and the cathode of the second diode. The anode of the second diode is connected to the second end of the fifth resistor, the first end of the sixth resistor, and the gate of the MOS transistor. The second end of the sixth resistor is connected to the first end of the seventh resistor, the first end of the eighth resistor, the source of the MOS transistor, and the first end of the third capacitor. The second end of the third capacitor is connected to the drain of the MOS transistor and serves as the output terminal of the switching circuit.

[0012] The second end of the seventh resistor is connected to the first end of the second capacitor and serves as the second output terminal of the switching circuit, used to connect to pin 4 of the power chip; the second end of the second capacitor is connected to the second end of the eighth resistor and grounded.

[0013] Preferably, the auxiliary circuit includes a third diode, a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, a thirteenth resistor, and a fourth capacitor;

[0014] The positive terminal of the third diode serves as the input terminal of the auxiliary circuit, and the positive terminal of the third diode is also connected to the first primary coil of the transformer.

[0015] The negative terminal of the third diode is connected to the first terminal of the ninth resistor and the first terminal of the tenth resistor, respectively. The second terminal of the ninth resistor is connected to the second terminal of the tenth resistor, the first terminal of the eleventh resistor, the first terminal of the twelfth resistor, the first terminal of the thirteenth resistor, and the first terminal of the fourth capacitor, respectively.

[0016] The second end of the eleventh resistor is connected to the second end of the twelfth resistor, the second end of the thirteenth resistor, and the second end of the fourth capacitor, respectively, and serves as the output end of the auxiliary circuit.

[0017] Preferably, the output circuit includes a fourth diode, a fifth diode, a fifth capacitor, a sixth capacitor, a fourteenth resistor, a fifteenth resistor, a sixteenth resistor, a first electrolytic capacitor, a second electrolytic capacitor, and a third electrolytic capacitor;

[0018] The anode of the fourth diode is connected to the anode of the fifth diode and serves as the input terminal of the output circuit. The cathode of the fourth diode is connected to the cathode of the fifth diode. The anode of the fifth diode is also connected to the first terminal of the fourteenth resistor. The second terminal of the fourteenth resistor is connected to the first terminal of the fifth capacitor. The second terminal of the fifth capacitor is connected to the first terminal of the sixth capacitor, the first terminal of the fifteenth resistor, the anode of the first electrolytic capacitor, the anode of the second electrolytic capacitor, and the anode of the third electrolytic capacitor. The second terminal of the sixth capacitor is connected to the second terminal of the fifteenth resistor, the cathode of the first electrolytic capacitor, the cathode of the second electrolytic capacitor, and the cathode of the third electrolytic capacitor, and is grounded.

[0019] The second end of the fifteenth resistor is also connected to the first end of the sixteenth resistor. The second end of the sixteenth resistor and the first end of the fifteenth resistor together serve as the output terminal of the output circuit, which is used to connect to the external projector.

[0020] Preferably, the conversion circuit includes a sixth diode, a fourth electrolytic capacitor, a seventeenth resistor, an eighteenth resistor, and a nineteenth resistor;

[0021] The anode of the sixth diode serves as the input terminal of the conversion circuit. The anode of the sixth diode is connected to the first terminal of the seventeenth resistor, and the cathode of the sixth diode is connected to the first terminal of the nineteenth resistor. The second terminal of the seventeenth resistor is connected to the first terminal of the eighteenth resistor, and the second terminal of the eighteenth resistor is connected to the first terminal of the nineteenth resistor and the anode of the fourth electrolytic capacitor. The cathode of the fourth electrolytic capacitor is grounded. The anode of the fourth electrolytic capacitor is also used to output the operating voltage.

[0022] Preferably, the first diode is an ES1JL diode.

[0023] Preferably, the thermistor is an SDNG104F3950 resistor.

[0024] Compared with the prior art, the beneficial effect of the present invention is that by connecting the output terminal of the switching circuit to the input terminal of the auxiliary circuit, the output terminal of the auxiliary circuit to the first primary coil of the transformer, and the output terminal of the secondary protection circuit to the second primary coil of the transformer; the first primary coil of the transformer is connected to the input terminal of the output circuit, and the output terminal of the output circuit is used to connect to an external projector; the second secondary coil of the transformer is connected to the input terminal of the conversion circuit, and the output terminal of the conversion circuit is used to output the working voltage; the first end of the first resistor serves as the first input terminal of the secondary protection circuit, and is used to connect to pin 4 of the power chip; the second end of the first resistor is connected to the first end of the thermistor, the second end of the thermistor is connected to the negative terminal of the first diode, the positive terminal of the first diode is connected to the first end of the second resistor and serves as the output terminal of the secondary protection circuit; the second end of the second resistor is connected to the first end of the third resistor, the second end of the third resistor is connected to the first end of the first capacitor and grounded; in this way, by adding an NTC thermistor next to the heat sink of the MOSFET, the temperature of the heat sink is detected. Once the temperature of the heat sink continues to rise, it indicates that the MOSFET power device is working abnormally. A protection value can be set. If the temperature of the heat sink exceeds this protection value, the power supply VCC is cut off, and the power chip directly stops working, thus truly achieving the protection function. Attached Figure Description

[0025] The present invention will now be described in detail with reference to the accompanying drawings. The above and other aspects of the present invention will become clearer and more readily understood through the detailed description following the accompanying drawings. In the drawings:

[0026] Figure 1 This is a circuit diagram of a projector switching power supply circuit with protection function provided in an embodiment of the present invention;

[0027] Figure 2 This is a circuit diagram of the secondary protection circuit provided in an embodiment of the present invention.

[0028] Among them, 1. Switching circuit, 2. Auxiliary circuit, 3. Secondary protection circuit, 4. Output circuit, and 5. Conversion circuit. Detailed Implementation

[0029] 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.

[0030] Combined with appendix Figures 1-2 As shown, this embodiment of the invention provides a projector switching power supply circuit with protection function, including: a power supply, a power chip U3, a switching circuit 1, an auxiliary circuit 2, a secondary protection circuit 3, a transformer T2, an output circuit 4, and a conversion circuit 5.

[0031] Pin 1 of the power chip U3 is grounded, and pin 2 of the power chip U3 is used for voltage feedback. Pins 3 and 4 of the power chip U3 are respectively connected to the input terminals of the secondary protection circuit 3. The power supply circuit is connected to pin 5 of the power chip U3 to supply power to the power chip U3. Pin 6 of the power chip U3 is connected to the input terminal of the switching circuit 1. The output terminal of the switching circuit 1 is connected to the input terminal of the auxiliary circuit 2. The output terminal of the auxiliary circuit 2 is connected to the first primary coil of the transformer T2. The output terminal of the secondary protection circuit 3 is connected to the second primary coil of the transformer T2. The first primary coil of the transformer T2 is connected to the input terminal of the output circuit 4. The output terminal of the output circuit 4 is used to connect to an external projector. The second primary coil of the transformer T2 is connected to the input terminal of the conversion circuit 5. The output terminal of the conversion circuit 5 is used to output the operating voltage.

[0032] The secondary protection circuit 3 includes a first diode D20, a thermistor NTC1, a first resistor R70, a second resistor R37, a third resistor R47, and a first capacitor C19. The first terminal of the first resistor R70 serves as the first input terminal of the secondary protection circuit 3, connected to pin 4 of the power chip U3. The second terminal of the first resistor R70 is connected to the first terminal of the thermistor NTC1, and the second terminal of the thermistor NTC1 is connected to the cathode of the first diode D20. The anode of the first diode D20 is connected to the first terminal of the second resistor R37 and serves as the output terminal of the secondary protection circuit 3. The second terminal of the second resistor R37 is connected to the first terminal of the third resistor R47, and the second terminal of the third resistor R47 is connected to the first terminal of the first capacitor C19 and grounded. The second terminal of the first capacitor C19 is connected to the first terminal of the third resistor R47 and serves as the second input terminal of the secondary protection circuit 3, connected to pin 3 of the power chip U3.

[0033] Specifically, the output of switching circuit 1 is connected to the input of auxiliary circuit 2, the output of auxiliary circuit 2 is connected to the first primary coil of transformer T2, and the output of secondary protection circuit 3 is connected to the second primary coil of transformer T2. The first primary coil of transformer T2 is connected to the input of output circuit 4, and the output of output circuit 4 is used to connect to an external projector. The second secondary coil of transformer T2 is connected to the input of conversion circuit 5, and the output of conversion circuit 5 is used to output the working voltage. The first end of the first resistor R70 serves as the first input of secondary protection circuit 3, and is used to connect to pin 4 of power chip U3. The second end of the first resistor R70 is connected to the first end of thermistor NTC1. The second terminal is connected to the negative terminal of the first diode D20, and the positive terminal of the first diode D20 is connected to the first terminal of the second resistor R37 and serves as the output terminal of the secondary protection circuit 3. The second terminal of the second resistor R37 is connected to the first terminal of the third resistor R47, and the second terminal of the third resistor R47 is connected to the first terminal of the first capacitor C19 and grounded. In this way, by adding an NTC thermistor NTC1 next to the heat sink of the MOSFET, the temperature of the heat sink can be detected. Once the temperature of the heat sink continues to rise, it means that the MOSFET power device is working abnormally. A protection value can be set. If the temperature of the heat sink exceeds this protection value, the power supply VCC is cut off, and the power chip U3 does not work directly, thus truly playing a protective role.

[0034] In this embodiment, the switching circuit 1 includes a fourth resistor R41, a fifth resistor R43, a sixth resistor R55, a seventh resistor R53, an eighth resistor R54, a second diode D8, a second capacitor C22, a third capacitor C4, and a MOSFET Q2. The first end of the fourth resistor R41 serves as the first input terminal of the switching circuit 1 and is connected to pin 6 of the power chip U3. The second end of the fourth resistor R41 is connected to the first end of the fifth resistor R43 and the cathode of the second diode D8. The anode of the second diode D8 is connected to the second end of the fifth resistor R43, the first end of the sixth resistor R55, and the gate of the MOSFET Q2. The second end of the sixth resistor R55 is connected to the first end of the seventh resistor R53, the first end of the eighth resistor R54, the source of the MOSFET Q2, and the first end of the third capacitor C4. The second end of the third capacitor C4 is connected to the drain of the MOSFET Q2 and serves as the output terminal of the switching circuit 1. The second end of the seventh resistor R53 is connected to the first end of the second capacitor C22 and serves as the second output terminal of the switching circuit 1, used to connect to pin 4 of the power chip U3. The second end of the second capacitor C22 is connected to the second end of the eighth resistor R54 and grounded.

[0035] In this embodiment, the auxiliary circuit 2 includes a third diode D1, a ninth resistor R30, a tenth resistor R29, an eleventh resistor R26, a twelfth resistor R27, a thirteenth resistor R60, and a fourth capacitor C11. The positive terminal of the third diode D1 serves as the input terminal of the auxiliary circuit 2, and the positive terminal of the third diode D1 is also connected to the first primary coil of the transformer T2. The negative terminal of the third diode D1 is connected to the first terminal of the ninth resistor R30 and the first terminal of the tenth resistor R29. The second terminal of the ninth resistor R30 is connected to the second terminal of the tenth resistor R29, the first terminal of the eleventh resistor R26, the first terminal of the twelfth resistor R27, the first terminal of the thirteenth resistor R60, and the first terminal of the fourth capacitor C11. The second terminal of the eleventh resistor R26 is connected to the second terminal of the twelfth resistor R27, the second terminal of the thirteenth resistor R60, and the second terminal of the fourth capacitor C11, and serves as the output terminal of the auxiliary circuit 2.

[0036] In this embodiment, the output circuit 4 includes a fourth diode D4, a fifth diode D5, a fifth capacitor C9, a sixth capacitor C15, a fourteenth resistor R21, a fifteenth resistor R31, a sixteenth resistor R18, a first electrolytic capacitor EC6, a second electrolytic capacitor EC7, and a third electrolytic capacitor EC8. The anode of the fourth diode D4 is connected to the anode of the fifth diode D5 and serves as the input terminal of the output circuit 4. The cathode of the fourth diode D4 is connected to the cathode of the fifth diode D5. The anode of the fifth diode D5 is also connected to the first terminal of the fourteenth resistor R21. The second terminal of the fourteenth resistor R21 is connected to the first terminal of the fifth capacitor C9. The second terminal of the fifth capacitor C9 is connected to... The first terminal of the sixth capacitor C15, the first terminal of the fifteenth resistor R31, the positive terminal of the first electrolytic capacitor EC6, the positive terminal of the second electrolytic capacitor EC7, and the positive terminal of the third electrolytic capacitor EC8 are connected to the first terminal of the fifteenth resistor R31, the negative terminal of the first electrolytic capacitor EC6, the negative terminal of the second electrolytic capacitor EC7, and the negative terminal of the third electrolytic capacitor EC8, respectively, and grounded; the second terminal of the fifteenth resistor R31 is also connected to the first terminal of the sixteenth resistor R18, and the second terminal of the sixteenth resistor R18 and the first terminal of the fifteenth resistor R31 together serve as the output terminal of the output circuit 4, which is used to connect to the external projector LED.

[0037] In this embodiment, the conversion circuit 5 includes a sixth diode D2, a fourth electrolytic capacitor EC9, a seventeenth resistor R3, an eighteenth resistor R13, and a nineteenth resistor R34. The anode of the sixth diode D2 serves as the input terminal of the conversion circuit 5. The anode of the sixth diode D2 is connected to the first terminal of the seventeenth resistor R3, and the cathode of the sixth diode D2 is connected to the first terminal of the nineteenth resistor R34. The second terminal of the seventeenth resistor R3 is connected to the first terminal of the eighteenth resistor R13, and the second terminal of the eighteenth resistor R13 is connected to the first terminal of the nineteenth resistor R34 and the anode of the fourth electrolytic capacitor EC9. The cathode of the fourth electrolytic capacitor EC9 is grounded. The anode of the fourth electrolytic capacitor EC9 is also used to output the operating voltage VDD.

[0038] In this embodiment, the first diode D20 is an ES1JL diode. It can handle a current of 1A and a voltage of 600V.

[0039] In this embodiment, the thermistor NTC1 is model SDNG104F3950. The thermistor NTC1 has a resistance of 100KΩ and a current carrying capacity of 1mA. The first resistor R70 has a resistance of 12KΩ.

[0040] The working principle of this invention is as follows:

[0041] The AC power supply provides high voltage to charge the VCC capacitor of the power chip U3. When the VCC voltage reaches VCC-on, the DR pin of the power chip U3 drives the MOSFET Q2 to conduct. The primary winding of the transformer T2 stores energy. After a certain duty cycle ton time, the DR pin goes low and turns off the MOSFET Q2. The secondary winding releases energy to charge the secondary capacitor. The output detection circuit detects the output voltage and current and feeds them back to U3 to control the duty cycle of the MOSFET, thereby stabilizing the output voltage and current.

[0042] When the switch is turned off, the turn-off voltage of the auxiliary winding charges the CS pin of the power chip U3 through the circuit of the first diode D20, the thermistor NTC1, and the first resistor R70; the voltage of the CS pin is raised, and after the Tshotp time is shielded, the CS pin is sampled and compared with Votp. If it is higher than the set value and the duration is greater than the chip Totp, it is determined that OTP protection has occurred and the system restarts.

[0043] When the power board malfunctions, the temperature of MOSFET Q2 continues to rise. As the heat sink temperature rises, the resistance of the NTC decreases due to its temperature resistance characteristics, resulting in a smaller voltage drop. The voltage at the CS pin increases, and when it reaches the protection setting value, the power board is determined to have experienced an overpower phenomenon. VCC is then cut off, and the chip stops working.

[0044] However, once a fault is detected, the chip immediately stops switching. Subsequently, the VCC voltage drops because the chip cannot be powered through the auxiliary winding. When the VCC voltage drops to the turn-off voltage VCC_UVLO, the protection logic is reset, and the chip's operating current simultaneously decreases to the startup current. The VCC voltage then rises again. When the VCC voltage exceeds the turn-on voltage VCC_ST, the switching action restarts. If the fault persists, the system will continue to repeat the above protection actions; otherwise, the system returns to normal operation. Using these functions, the system can selectively start and stop switching actions until the fault disappears, thereby improving the projector's reliability.

[0045] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, article, or apparatus that includes that element.

[0046] The embodiments of the present invention have been described above with reference to the accompanying drawings. The disclosed embodiments are merely preferred embodiments of the present invention. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many equivalent changes in form without departing from the spirit and scope of the claims of the present invention, and all such changes are within the protection scope of the present invention.

Claims

1. A projector switching power supply circuit with protection function, characterized in that, include: Power supply, power chip, switching circuit, auxiliary circuit, secondary protection circuit, transformer, output circuit and conversion circuit; Pin 1GND of the power chip is grounded, and pin 2FB is used for voltage feedback. Pins 3DET and 4CS of the power chip are respectively connected to the input terminals of the secondary protection circuit. The power supply is connected to pin 5VCC of the power chip to power it. Pin 6DRV of the power chip is connected to the input terminal of the switching circuit. The output terminal of the switching circuit is connected to the input terminal of the auxiliary circuit. The output terminal of the auxiliary circuit is connected to the first primary coil of the transformer. The output terminal of the secondary protection circuit is connected to the second primary coil of the transformer. The first primary coil of the transformer is connected to the input terminal of the output circuit, and the output terminal of the output circuit is used to connect to an external projector. The second primary coil of the transformer is connected to the input terminal of the conversion circuit, and the output terminal of the conversion circuit is used to output the operating voltage. The secondary protection circuit includes a first diode, a thermistor, a first resistor, a second resistor, a third resistor, and a first capacitor. The first terminal of the first resistor serves as the first input terminal of the secondary protection circuit, connected to pin 4CS of the power chip. The second terminal of the first resistor is connected to the first terminal of the thermistor, and the second terminal of the thermistor is connected to the cathode of the first diode. The anode of the first diode is connected to the first terminal of the second resistor and serves as the output terminal of the secondary protection circuit. The second terminal of the second resistor is connected to the first terminal of the third resistor, and the second terminal of the third resistor is connected to the first terminal of the first capacitor and grounded. The second end of the first capacitor is connected to the first end of the third resistor and serves as the second input terminal of the secondary protection circuit, which is used to connect to pin 3DET of the power chip.

2. The projector switching power supply circuit with protection function as described in claim 1, characterized in that, The switching circuit includes a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a second diode, a second capacitor, a third capacitor, and a MOSFET; The first end of the fourth resistor serves as the first input terminal of the switching circuit and is connected to pin 6DRV of the power chip. The second end of the fourth resistor is connected to the first end of the fifth resistor and the cathode of the second diode. The anode of the second diode is connected to the second end of the fifth resistor, the first end of the sixth resistor, and the gate of the MOSFET. The second end of the sixth resistor is connected to the first end of the seventh resistor, the first end of the eighth resistor, the source of the MOSFET, and the first end of the third capacitor. The second end of the third capacitor is connected to the drain of the MOSFET and serves as the output terminal of the switching circuit. The second end of the seventh resistor is connected to the first end of the second capacitor and serves as the second output terminal of the switching circuit, used to connect to pin 4CS of the power chip; the second end of the second capacitor is connected to the second end of the eighth resistor and grounded.

3. The projector switching power supply circuit with protection function as described in claim 1, characterized in that, The auxiliary circuit includes a third diode, a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, a thirteenth resistor, and a fourth capacitor; The positive terminal of the third diode serves as the input terminal of the auxiliary circuit, and the positive terminal of the third diode is also connected to the first primary coil of the transformer. The negative terminal of the third diode is connected to the first terminal of the ninth resistor and the first terminal of the tenth resistor, respectively. The second terminal of the ninth resistor is connected to the second terminal of the tenth resistor, the first terminal of the eleventh resistor, the first terminal of the twelfth resistor, the first terminal of the thirteenth resistor, and the first terminal of the fourth capacitor, respectively. The second end of the eleventh resistor is connected to the second end of the twelfth resistor, the second end of the thirteenth resistor, and the second end of the fourth capacitor, respectively, and serves as the output end of the auxiliary circuit.

4. The projector switching power supply circuit with protection function as described in claim 1, characterized in that, The output circuit includes a fourth diode, a fifth diode, a fifth capacitor, a sixth capacitor, a fourteenth resistor, a fifteenth resistor, a sixteenth resistor, a first electrolytic capacitor, a second electrolytic capacitor, and a third electrolytic capacitor; The anode of the fourth diode is connected to the anode of the fifth diode and serves as the input terminal of the output circuit. The cathode of the fourth diode is connected to the cathode of the fifth diode. The anode of the fifth diode is also connected to the first terminal of the fourteenth resistor. The second terminal of the fourteenth resistor is connected to the first terminal of the fifth capacitor. The second terminal of the fifth capacitor is connected to the first terminal of the sixth capacitor, the first terminal of the fifteenth resistor, the anode of the first electrolytic capacitor, the anode of the second electrolytic capacitor, and the anode of the third electrolytic capacitor. The second terminal of the sixth capacitor is connected to the second terminal of the fifteenth resistor, the cathode of the first electrolytic capacitor, the cathode of the second electrolytic capacitor, and the cathode of the third electrolytic capacitor, and is grounded. The second end of the fifteenth resistor is also connected to the first end of the sixteenth resistor. The second end of the sixteenth resistor and the first end of the fifteenth resistor together serve as the output terminal of the output circuit, which is used to connect to the external projector.

5. The projector switching power supply circuit with protection function as described in claim 1, characterized in that, The conversion circuit includes a sixth diode, a fourth electrolytic capacitor, a seventeenth resistor, an eighteenth resistor, and a nineteenth resistor; The anode of the sixth diode serves as the input terminal of the conversion circuit. The anode of the sixth diode is connected to the first terminal of the seventeenth resistor, and the cathode of the sixth diode is connected to the first terminal of the nineteenth resistor. The second terminal of the seventeenth resistor is connected to the first terminal of the eighteenth resistor, and the second terminal of the eighteenth resistor is connected to the first terminal of the nineteenth resistor and the anode of the fourth electrolytic capacitor. The cathode of the fourth electrolytic capacitor is grounded. The anode of the fourth electrolytic capacitor is also used to output the operating voltage.

6. The projector switching power supply circuit with protection function as described in claim 1, characterized in that, The first diode is an ES1JL diode.

7. The projector switching power supply circuit with protection function as described in claim 1, characterized in that, The thermistor is an SDNG104F3950 resistor.

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