A single-stage LLC switching power supply circuit

Abstract

The present invention discloses a single-stage LLC switching power supply circuit, which is characterized by including an EMI filtering module, an APFC boost module, an LLC resonance module, an output module, a feedback module, a control module and a load. The first input end of the EMI filtering module is connected to one end of an external AC power supply, and the second input end of the EMI filtering module is connected to the other end of the external AC power supply. The APFC boost module includes a first inductor, a first diode, a second diode, a first capacitor, a first NMOS transistor and a second NMOS transistor. The LLC resonance module includes a second inductor, a second capacitor and a transformer. The transformer includes a primary winding, an auxiliary winding, a first secondary winding and a second secondary winding. The output module includes a third diode, a fourth diode, a third capacitor and a third inductor. The advantage is that while completing boost energy storage, the LLC resonance module also completes the resonance process to transfer energy to the secondary coil, simplifies the circuit structure and reduces costs.

Description

Technical Field

[0001] The present invention relates to a switching power supply circuit, and in particular to a single-stage LLC switching power supply circuit. Background Art

[0002] A switching power supply is a circuit that converts high-voltage alternating current into low-voltage direct current electrical energy. The switching power supply mainly consists of a rectification module, a control circuit, a transformer, a secondary rectification circuit, a filtering circuit, and a feedback circuit, etc. The complex design of the switching power supply results in many indicators, and the power factor is an important indicator in high-power switching power supplies; the power factor refers to the relationship between the active power and the apparent power, that is, the ratio of the active power divided by the apparent power. When the power factor value is larger, it means the higher the power utilization rate. The realization of a high power factor is often achieved through a power factor correction (Power Factor Correction, abbreviated as PFC) circuit. Most PFC circuits mainly adopt the active power factor correction (Active Power Factor Correction, abbreviated as APFC) method, which mainly consists of a PFC controller, a boost inductor, a boost diode, an output capacitor, and a power transistor. The PFC controller adjusts the phase of the output voltage and output current during the entire boost and energy storage processes to improve the power factor of the circuit.

[0003] At present, most of the switching power supply products on the market adopt a two-stage switching power supply that combines a PFC circuit with a hard-switching switching power supply. The disadvantage of this two-stage switching power supply is that there is a certain stray inductance in the loop formed by the switching transistor, the boost diode, and the output filter capacitor. At a certain frequency, it is easy to generate a dangerous overvoltage, which is not conducive to the safe operation of the switching transistor in the hard-switching state. In addition, this structure itself is complex, with more circuit components, increasing the circuit design cost of the system and causing difficulties in maintenance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a single-stage LLC switching power supply circuit with a simple structure and a high power factor.

[0005] The technical solution adopted by the present invention to solve the above technical problems is as follows: A single-stage LLC switching power supply circuit includes an EMI filtering module, an APFC boost module, an LLC resonance module, an output module, a feedback module, a control module, and a load. The first input end of the EMI filtering module is connected to one end of an external AC power supply, and the second input end of the EMI filtering module is connected to the other end of the external AC power supply. The APFC boost module includes a first inductor, a first diode, a second diode, a first capacitor, a first NMOS transistor, and a second NMOS transistor. The LLC resonance module includes a second inductor, a second capacitor, and a transformer. The transformer includes a primary winding, an auxiliary winding, a first secondary winding, and a second secondary winding. The output module includes a third diode, a fourth diode, a third capacitor, and a third inductor. One end of the first inductor is connected to the first output end of the EMI filtering module. The other end of the first inductor, the positive electrode of the first diode, and the negative electrode of the second diode are connected. The negative electrode of the first diode, one end of the first capacitor, the drain of the first NMOS transistor, and the start voltage input end of the control module are connected. The positive electrode of the second diode is connected to the other end of the first capacitor. The second output end of the EMI filtering module, the source of the first NMOS transistor, the drain of the second NMOS transistor, and one end of the second inductor are connected. The other end of the second inductor is connected to one end of the primary winding. The other end of the primary winding is connected to one end of the second capacitor. The source of the second NMOS transistor, the other end of the second capacitor, and one end of the auxiliary winding are connected in parallel to the primary ground. The other end of the auxiliary winding is used to connect to the working voltage input end of the control module. One end of the first secondary winding is connected to the negative electrode of the third diode. The other end of the first secondary winding, one end of the second secondary winding, one end of the third capacitor, one end of the third inductor, and the first voltage detection end of the feedback module are connected. The other end of the second secondary winding is connected to the negative electrode of the fourth diode. The other end of the third inductor, one end of the load, and the second voltage detection end of the feedback module are connected. The positive electrode of the third diode, the positive electrode of the fourth diode, the other end of the third capacitor, and the other end of the load are connected in parallel to the secondary ground. The feedback module is used to obtain the voltage at one end of the third inductor through the first voltage detection end and send a voltage detection signal to the control module. The control module is used to send a first resonance control signal to the gate of the first NMOS transistor and simultaneously send a second resonance control signal to the gate of the second NMOS transistor according to the received voltage detection signal.

[0006] The feedback module includes a first resistor, a second resistor, a third resistor, a fourth resistor, a precision voltage regulator TL431, and an optocoupler PC817. The control module includes a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, and a ninth resistor. One end of the first resistor is connected to one end of the third inductor. The other end of the first resistor, one end of the second resistor, and the positive pole of the transmitting end of the optocoupler are connected. The negative pole of the transmitting end of the optocoupler, the other end of the second resistor, and the negative pole of the precision voltage regulator are connected. The receiving end of the optocoupler is used to send a voltage detection signal to the control module. One end of the third resistor is connected to the other end of the third inductor. The other end of the third resistor, one end of the fourth resistor, and the control terminal of the precision voltage regulator are connected. The positive pole of the precision voltage regulator is connected in parallel with the other end of the fourth resistor to the secondary ground.

[0007] The control module includes a power supply chip NCP1399, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, a fourth capacitor, a fifth diode, and a zener diode. One end of the fifth resistor is connected to one end of the first capacitor. The other end of the fifth resistor is connected to the HV pin of the power supply chip. One end of the sixth resistor is connected to the MODE pin of the power supply chip. The other end of the sixth resistor, one end of the seventh resistor, and the BULK pin of the power supply chip are connected. The other end of the seventh resistor is connected to the primary ground. The FB pin of the power supply chip is connected to the positive pole of the receiving end of the optocoupler. The negative pole of the receiving end of the optocoupler is connected to the primary ground. The MU pin of the power supply chip is connected to one end of the ninth resistor. The other end of the ninth resistor is connected to the gate of the first NMOS transistor. The ML pin of the power supply chip is connected to one end of the tenth resistor. The other end of the tenth resistor is connected to the gate of the second NMOS transistor. The VCC pin of the power supply chip, one end of the fourth capacitor, and the negative pole of the fifth diode are connected. The other end of the fourth capacitor is connected to the primary ground. The positive pole of the fifth diode, the other end of the auxiliary winding, and one end of the eighth resistor are connected. The other end of the eighth resistor, the negative pole of the zener diode, and the OVP pin of the power supply chip are connected. The positive pole of the zener diode is connected to the primary ground. The external DC voltage provides the startup voltage for the power supply chip. After the power supply chip works for a period of time, the external DC voltage is disconnected, and the other end of the auxiliary winding provides the continuous working voltage.

[0008] The EMI filtering module described above includes an overcurrent protection unit including a fuse, a varistor, a first safety capacitor, a second safety capacitor, and a common mode inductor. One end of the fuse is connected to one end of the external AC power supply. The other end of the fuse, one end of the varistor, one end of the first safety capacitor, and the first input terminal of the common mode inductor are connected. The other end of the external AC power supply, the other end of the varistor, the other end of the first safety capacitor, and the second input terminal of the common mode inductor are connected. The first output terminal of the common mode inductor, one end of the second safety capacitor, and one end of the first inductor are connected. The second output terminal of the common mode inductor, the other end of the second safety capacitor, and one end of the second inductor are connected. The AC power supply is filtered by the EMI filtering module to remove the clutter during power supply and also suppress the high-frequency clutter generated by the LLC resonance module from being transmitted to the power grid. Moreover, when the current exceeds the set value, the fuse can be blown, and when the voltage is too high, the varistor can be turned on, playing a role in protecting the subsequent modules.

[0009] Compared with the prior art, the advantages of the present invention are as follows: in the circuit structure, by utilizing the soft-switching characteristics of the LLC resonance module, the turn-on losses of the first NMOS transistor and the second NMOS transistor are reduced, greatly improving the efficiency of the power supply system; the output module feeds back the voltage detection signal output to the load to the control module through the feedback module, which can not only adjust the resonance frequency according to the load size but also complete the energy storage of the first inductor and the release of electrical energy from the first capacitor to the LLC resonance module by using the same first NMOS transistor or second NMOS transistor within one cycle, achieving not only a high power factor but also greatly simplifying the circuit structure; the control module adjusts the resonance frequency of the LLC resonance module by controlling the switching frequency of the first NMOS transistor or the second NMOS transistor through the voltage detection signal of the feedback module. When the load decreases, the resonance frequency increases, the peak current of the APFC boost module decreases, and the effective value of the current of the corresponding LLC resonance module also decreases.

[0010] During the same moment when the entire switching power supply circuit operates normally, the APFC boost module and the LLC resonance module share the same first NMOS transistor or second NMOS transistor, completing the resonance process of the LLC resonance module while achieving boost energy storage and transferring energy to the secondary coil; adopting this active power factor boost topology structure greatly simplifies the power factor correction circuit, eliminates some redundant overvoltage and overcurrent protection structures in the two-stage switching power supply, and reduces the circuit design cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is the circuit principle block diagram of the present invention;

[0012] Figure 2 Partial circuit structure diagram of the present invention;

[0013] Figure 3 Circuit structure diagram of the control module in the present invention;

[0014] Figure 4 Circuit structure diagram of the EMI filtering module in the present invention. Specific embodiments

[0015] The present invention will be further described in detail below in conjunction with the embodiments with reference to the drawings.

[0016] A single-stage LLC switching power supply circuit includes an EMI filtering module 1, an APFC boost module 2, an LLC resonance module 3, an output module 4, a feedback module 5, a control module 6, and a load (not shown in the figure). The first input terminal of the EMI filtering module 1 is connected to one end of an external AC power supply U, and the second input terminal of the EMI filtering module 1 is connected to the other end of the external AC power supply U. The APFC boost module 2 includes a first inductor L1, a first diode D1, a second diode D2, a first capacitor C1, a first NMOS transistor Q1, and a second NMOS transistor Q2. The LLC resonance module 3 includes a second inductor L2, a second capacitor C2, and a transformer T1. The transformer T1 includes a primary winding Lm1, an auxiliary winding Lm2, a first secondary winding Ln1, and a second secondary winding Ln2. The output module 4 includes a third diode D3, a fourth diode D4, a third capacitor C3, and a third inductor L3. One end of the first inductor L1 is connected to the first output terminal of the EMI filtering module 1, and the other end of the first inductor L1, the positive electrode of the first diode D1, and the negative electrode of the second diode D2 are connected. The negative electrode of the first diode D1, one end of the first capacitor C1, the drain of the first NMOS transistor Q1, and the startup voltage input terminal of the control module 6 are connected. The positive electrode of the second diode D2 is connected to the other end of the first capacitor C1. The second output terminal of the EMI filtering module 1, the source of the first NMOS transistor Q1, the drain of the second NMOS transistor Q2, and one end of the second inductor L2 are connected. The other end of the second inductor L2 is connected to one end of the primary winding Lm1. The other end of the primary winding Lm1 is connected to one end of the second capacitor C2. The source of the second NMOS transistor Q2, the other end of the second capacitor C2, and one end of the auxiliary winding Lm2 are connected in parallel to the primary ground. The other end of the auxiliary winding Lm2 is used to connect to the operating voltage input terminal of the control module 6. One end of the first secondary winding Ln1 is connected to the negative electrode of the third diode D3. The other end of the first secondary winding Ln1, one end of the second secondary winding Ln2, one end of the third capacitor C3, one end of the third inductor L3, and the first voltage detection terminal of the feedback module 5 are connected. The other end of the second secondary winding Ln2 is connected to the negative electrode of the fourth diode D4. The other end of the third inductor L3, one end of the load, and the second voltage detection terminal of the feedback module 5 are connected. The positive electrodes of the third diode D3, the fourth diode D4, the other end of the third capacitor C3, and the other end of the load are connected in parallel to the secondary ground. The feedback module 5 is used to obtain the voltage at one end of the third inductor L3 through the first voltage detection terminal and send a voltage detection signal to the control module 6. The control module 6 is used to send a first resonance control signal to the gate of the first NMOS transistor Q1 according to the received voltage detection signal, and at the same time send a second resonance control signal to the gate of the second NMOS transistor Q2.

[0017] The feedback module 5 includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a precision voltage regulator ZD1 of model TL431, and an optocoupler PC1 of model PC817. The control module 6 includes a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, and a ninth resistor R9. One end of the first resistor R1 is connected to one end of the third inductor L3. The other end of the first resistor R1, one end of the second resistor R2, and the positive electrode of the transmitting end of the optocoupler PC1 are connected. The negative electrode of the transmitting end of the optocoupler PC1, the other end of the second resistor R2, and the negative electrode of the precision voltage regulator ZD1 are connected. The receiving end of the optocoupler PC1 is used to send a voltage detection signal to the control module 6. One end of the third resistor R3 is connected to the other end of the third inductor L3. The other end of the third resistor R3, one end of the fourth resistor R4, and the control end of the precision voltage regulator ZD1 are connected. The positive electrode of the precision voltage regulator ZD1 is connected in parallel with the other end of the fourth resistor R4 to the secondary ground.

[0018] The control module 6 includes a power supply chip U1 of model NCP1399, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, a fourth capacitor C4, a fifth diode D5, and a zener diode ZD2. One end of the fifth resistor R5 is connected to one end of the first capacitor C1. The other end of the fifth resistor R5 is connected to the HV pin of the power supply chip U1. One end of the sixth resistor R6 is connected to the MODE pin of the power supply chip U1. The other end of the sixth resistor R6, one end of the seventh resistor R7, and the BULK pin of the power supply chip U1 are connected. The other end of the seventh resistor R7 is connected to the primary ground. The FB pin of the power supply chip U1 is connected to the positive electrode of the receiving end of the optocoupler PC1. The negative electrode of the receiving end of the optocoupler PC1 is connected to the primary ground. The MU pin of the power supply chip U1 is connected to one end of the ninth resistor R9. The other end of the ninth resistor R9 is connected to the gate of the first NMOS transistor Q1. The ML pin of the power supply chip U1 is connected to one end of the tenth resistor R10. The other end of the tenth resistor R10 is connected to the gate of the second NMOS transistor Q2. The VCC pin of the power supply chip U1, one end of the fourth capacitor C4, and the negative electrode of the fifth diode D5 are connected. The other end of the fourth capacitor C4 is connected to the primary ground. The positive electrode of the fifth diode D5, the other end of the auxiliary winding Lm2, and one end of the eighth resistor R8 are connected. The other end of the eighth resistor R8, the negative electrode of the zener diode ZD2, and the OVP pin of the power supply chip U1 are connected. The positive electrode of the zener diode ZD2 is connected to the primary ground.

[0019] The EMI filtering module 1 includes an overcurrent protection unit including a fuse FUSE, a varistor ZNR, a first safety capacitor CS1, a second safety capacitor CS2, and a common mode inductor LD1. One end of the fuse FUSE is connected to one end of an external AC power supply U. The other end of the fuse FUSE, one end of the varistor ZNR, one end of the first safety capacitor CS1, and the first input terminal of the common mode inductor LD1 are connected. The other end of the external AC power supply U, the other end of the varistor ZNR, the other end of the first safety capacitor CS1, and the second input terminal of the common mode inductor LD1 are connected. The first output terminal of the common mode inductor LD1, one end of the second safety capacitor CS2, and one end of the first inductor L1 are connected. The second output terminal of the common mode inductor LD1, the other end of the second safety capacitor CS2, and one end of the second inductor L2 are connected.

[0020] The specific principle of the above embodiments is as follows: After starting the power supply, the AC power supply U charges the first capacitor C1. In this stage, not only is energy stored in the first capacitor C1 for starting the power supply chip U1 of the control module 6, but also a part of the energy is stored in the first inductor L1. When the voltage on the first capacitor C1 reaches the startup threshold of the power supply chip U1 of the control module 6, the power supply chip U1 of the control module 6 starts and outputs a pulse to turn on the first NMOS transistor Q1. At this moment, there are two loops in the system. One is the inductor energy storage loop, and the other is the LLC resonance loop. The inductor energy storage loop goes from the AC power supply U to the first inductor L1, the first diode D1, the first NMOS transistor Q1, and then back to the AC power supply U. The LLC resonance loop discharges the first capacitor C1 to the LLC resonance module 3, from the first capacitor C1, the second inductor L2, the primary winding Lm1, the second capacitor C2, and then to the primary ground PGND. The first secondary winding Ln1 and the second secondary winding Ln2 of the transformer T1 are used as the output of the LLC resonance module 3, and charge the third capacitor C3 through the third diode D3 of the output module 4 and also supply power to the load.

[0021] After the primary winding Lm1 of the transformer T1 transfers energy to the two secondary windings, the first NMOS transistor Q1 continues to conduct, and the first inductor L1 continues to store energy. At this time, the magnitude of the magnetizing current on the magnetizing inductor of the primary winding Lm1 is the same as the magnitude of the resonant current of the second inductor L2, and there is no difference between the two. The load is powered by the third capacitor C3. When the first NMOS transistor Q1 conducts, on the one hand, the APFC boost module 2 needs to use the first NMOS transistor Q1 to form a boost circuit to store energy for the LLC resonant module 3 in the next cycle. At the same time, the first capacitor C1 releases the energy stored in the previous cycle to the LLC resonant module 3, and the energy is transferred to the output module 4 through the transformer T1 of the LLC resonant module 3. In one stage, the first NMOS transistor Q1 completes both boosting and resonance. After the primary winding Lm1 and the second inductor L2 participate in resonance at the same time and end, the first NMOS transistor Q1 turns off, and the LLC resonant module 3 enters the dead time stage. At this stage, the load is still powered by the third capacitor C3.

[0022] After the dead time ends, the second NMOS transistor Q2 conducts, and the first inductor L1 charges the first capacitor C1, and charges the third capacitor C3 through the fourth diode D4 of the output module 4 and also powers the load. After the primary winding Lm1 of the transformer T1 transfers energy to the two secondary windings, the second NMOS transistor Q2 still conducts, and the first inductor L1 continues to charge the first capacitor C1. At this time, the magnitude of the magnetizing current on the magnetizing inductor of the primary winding Lm1 is the same as the magnitude of the resonant current of the second inductor L2, and there is no difference between the two. The load is powered by the third capacitor C3 of the output module 4. In this stage, the APFC boost module 2 and the second NMOS transistor Q2 are used to form a boost circuit to store energy for the LLC resonant module 3 in the next cycle. At the same time, the primary winding Lm1 of the transformer T1 of the resonant module, the second capacitor C2, and the second inductor L2 form a resonant circuit for the second half cycle, and the primary winding Lm1 releases energy, and the energy is transferred to the secondary coil through the transformer T1. In one stage, the second NMOS transistor Q2 completes both boosting and the resonance function.

[0023] After the primary winding Lm1 and the second inductor L2 participate in resonance at the same time and end, the second NMOS transistor Q2 turns off, and the LLC resonant module 3 enters the dead time stage. At this moment, the load is still powered by the third capacitor C3.

Claims

1. A single-stage LLC switching power supply circuit, characterized in that It includes an EMI filtering module, an APFC boost module, an LLC resonant module, an output module, a feedback module, a control module and a load. The first input terminal of the EMI filtering module is connected to one end of an external AC power supply, and the second input terminal of the EMI filtering module is connected to the other end of the external AC power supply. The APFC boost module includes a first inductor, a first diode, a second diode, a first capacitor, a first NMOS transistor and a second NMOS transistor. The LLC resonant module includes a second inductor, a second capacitor and a transformer. The transformer includes a primary winding, an auxiliary winding, a first secondary winding and a second secondary winding. The output module includes a third diode, a fourth diode, a third capacitor and a third inductor. One end of the first inductor is connected to the first output terminal of the EMI filtering module. The other end of the first inductor, the positive electrode of the first diode and the negative electrode of the second diode are connected. The negative electrode of the first diode, one end of the first capacitor, the drain of the first NMOS transistor and the start voltage input terminal of the control module are connected. The positive electrode of the second diode is connected to the other end of the first capacitor. The second output terminal of the EMI filtering module, the source of the first NMOS transistor, the drain of the second NMOS transistor and one end of the second inductor are connected. The other end of the second inductor is connected to one end of the primary winding. The other end of the primary winding is connected to one end of the second capacitor. The source of the second NMOS transistor, the other end of the second capacitor and one end of the auxiliary winding are connected in parallel to the primary ground. The other end of the auxiliary winding is used to connect to the working voltage input terminal of the control module. One end of the first secondary winding is connected to the negative electrode of the third diode. The other end of the first secondary winding, one end of the second secondary winding, one end of the third capacitor, one end of the third inductor and the first voltage detection terminal of the feedback module are connected. The other end of the second secondary winding is connected to the negative electrode of the fourth diode. The other end of the third inductor, one end of the load and the second voltage detection terminal of the feedback module are connected. The positive electrode of the third diode, the positive electrode of the fourth diode, the other end of the third capacitor and the other end of the load are connected in parallel to the secondary ground. The feedback module is used to obtain the voltage at one end of the third inductor through the first voltage detection terminal and send a voltage detection signal to the control module. The control module is used to send a first resonant control signal to the gate of the first NMOS transistor and at the same time send a second resonant control signal to the gate of the second NMOS transistor according to the received voltage detection signal.

2. The single-stage LLC switching power supply circuit according to claim 1, characterized in that The feedback module includes a first resistor, a second resistor, a third resistor, a fourth resistor, a precision voltage regulator TL431, and an optocoupler PC817. The control module includes a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, and a ninth resistor. One end of the first resistor is connected to one end of the third inductor. The other end of the first resistor, one end of the second resistor, and the positive electrode of the transmitting end of the optocoupler are connected. The negative electrode of the transmitting end of the optocoupler, the other end of the second resistor, and the negative electrode of the precision voltage regulator are connected. The receiving end of the optocoupler is used to send a voltage detection signal to the control module. One end of the third resistor is connected to the other end of the third inductor. The other end of the third resistor, one end of the fourth resistor, and the control terminal of the precision voltage regulator are connected. The positive electrode of the precision voltage regulator is connected in parallel with the other end of the fourth resistor to the secondary ground.

3. The single-stage LLC switching power supply circuit according to claim 2, wherein The control module includes a power supply chip NCP1399, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, a fourth capacitor, a fifth diode, and a zener diode. One end of the fifth resistor is connected to one end of the first capacitor. The other end of the fifth resistor is connected to the HV pin of the power supply chip. One end of the sixth resistor is connected to the MODE pin of the power supply chip. The other end of the sixth resistor, one end of the seventh resistor, and the BULK pin of the power supply chip are connected. The other end of the seventh resistor is connected to the primary ground. The FB pin of the power supply chip is connected to the positive electrode of the receiving end of the optocoupler. The negative electrode of the receiving end of the optocoupler is connected to the primary ground. The MU pin of the power supply chip is connected to one end of the ninth resistor. The other end of the ninth resistor is connected to the gate of the first NMOS transistor. The ML pin of the power supply chip is connected to one end of the tenth resistor. The other end of the tenth resistor is connected to the gate of the second NMOS transistor. The VCC pin of the power supply chip, one end of the fourth capacitor, and the negative electrode of the fifth diode are connected. The other end of the fourth capacitor is connected to the primary ground. The positive electrode of the fifth diode, the other end of the auxiliary winding, and one end of the eighth resistor are connected. The other end of the eighth resistor, the negative electrode of the zener diode, and the OVP pin of the power supply chip are connected. The positive electrode of the zener diode is connected to the primary ground.

4. A single-stage LLC switching power supply circuit according to claim 1, wherein The EMI filtering module includes an overcurrent protection unit including a fuse, a varistor, a first safety capacitor, a second safety capacitor and a common mode inductor. One end of the fuse is connected to one end of the external AC power supply. The other end of the fuse, one end of the varistor, one end of the first safety capacitor and the first input end of the common mode inductor are connected. The other end of the external AC power supply, the other end of the varistor, the other end of the first safety capacitor and the second input end of the common mode inductor are connected. The first output end of the common mode inductor, one end of the second safety capacitor and one end of the first inductor are connected. The second output end of the common mode inductor, the other end of the second safety capacitor and one end of the second inductor are connected.

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