A PFC-LLC resonant switching power supply

Abstract

The application discloses a PFC-LLC resonant switching power supply, which comprises a PFC circuit and an LLC circuit, an input end of the PFC circuit is connected with an AC input interface, an output end of the PFC circuit is connected with an input end of the LLC circuit through a high-voltage bus, an output end of the LLC circuit is connected with a DC output interface, and the PFC-LLC resonant switching power supply further comprises a bus voltage sampling circuit, a fault detection circuit, a first enabling control circuit and a second enabling control circuit, an input end of the first enabling control circuit is connected with an output end of the fault detection circuit, an output end of the first enabling control circuit is connected with a voltage sampling end of a PFC control unit of the PFC circuit, a first input end of the second enabling control circuit is connected with the output end of the fault detection circuit, an output end of the second enabling control circuit is connected with a voltage feedback input end of an LLC control unit of the LLC circuit, an input end of the bus voltage sampling circuit is connected with the input end of the LLC circuit, and an output end of the bus voltage sampling circuit is connected with the voltage feedback input end of the LLC control unit.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more specifically to a PFC-LLC resonant switching power supply. Background Technology

[0002] In traditional PFC-LLC switching power supplies, the PFC and LLC circuits each rely on their own sampling circuits to detect anomalies, lacking a unified fault linkage mechanism. When the system requires an emergency shutdown, the two circuits cannot be synchronized and shut down quickly, resulting in a protection blind zone. Most solutions only use the bus voltage for PFC control, while the LLC typically relies on the output voltage or independent sampling, lacking direct monitoring of the bus voltage and unable to actively intervene in the LLC's operating state when the bus is undervoltage or overvoltage.

[0003] Traditional PFC-LLC switching power supplies are widely used due to their high efficiency and small size, but the high-speed switching of their power switching transistors generates strong electromagnetic interference. If not suppressed, this interference will be conducted to the power grid through the power lines, interfering with the normal operation of other electronic devices and failing to meet the requirements of electromagnetic compatibility standards.

[0004] EMI filters disclosed in related technologies are typically constructed using passive components, including common-mode inductors, X capacitors, and Y capacitors. To effectively suppress conducted interference in the low-frequency band, especially common-mode noise, a large common-mode inductor is required. However, the large size of the common-mode inductor has become a bottleneck limiting the improvement of power density and cost reduction in power supplies. Furthermore, the value of the Y capacitor is strictly limited by leakage current safety standards and cannot be arbitrarily increased, which further restricts the suppression effect of high-frequency common-mode noise.

[0005] Among related technologies, there are also some active EMI filtering solutions that cancel out the original noise by injecting anti-phase noise current. However, these solutions are usually complex circuits, requiring additional power supplies and complex control loops, resulting in high costs and low reliability, making them difficult to promote and apply in cost-sensitive small and medium power supplies. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art, and provides a PFC-LLC resonant switching power supply.

[0007] This invention discloses a PFC-LLC resonant switching power supply, including a PFC circuit and an LLC circuit. The input terminal of the PFC circuit is connected to an AC input interface, and the output terminal of the PFC circuit is connected to the input terminal of the LLC circuit via a high-voltage bus. The output terminal of the LLC circuit is connected to a DC output interface. The power supply also includes a bus voltage sampling circuit, a fault detection circuit, a first enable control circuit, and a second enable control circuit. The input terminal of the first enable control circuit is connected to the output terminal of the fault detection circuit, and its output terminal is connected to the voltage sampling terminal of the PFC control unit of the PFC circuit. The first input terminal of the second enable control circuit is connected to the output terminal of the fault detection circuit, and its output terminal is connected to the voltage feedback input terminal of the LLC control unit of the LLC circuit. The input terminal of the bus voltage sampling circuit is connected to the input terminal of the LLC circuit, and its output terminal is connected to the voltage feedback input terminal of the LLC control unit.

[0008] In some embodiments, an AC input pre-stage protection circuit is provided between the input terminal of the PFC circuit and the AC input interface. The AC input pre-stage protection circuit includes a first EMI filter circuit and a common-mode noise cancellation unit. The common-mode noise cancellation unit includes a sampling network, an operational amplifier, and an injection capacitor. The input terminal of the first EMI filter circuit is connected to the AC input interface. One end of the sampling network is connected to the first output terminal of the first EMI filter circuit, and the other end of the sampling network is connected to the second output terminal of the first EMI filter circuit. The sampling output point of the sampling network is connected to one input terminal of the operational amplifier. The output terminal of the operational amplifier is connected to one end of the injection capacitor, and the other end of the injection capacitor is connected to protective ground.

[0009] In some embodiments, the first EMI filter circuit includes a common-mode inductor L5, the first input terminal of the common-mode inductor L5 is connected to the live wire input terminal of the AC input interface, the second input terminal of the common-mode inductor L5 is connected to the neutral wire input terminal of the AC input interface, the first output terminal of the common-mode inductor L5 is connected to the first output terminal of the first EMI filter circuit, and the second output terminal of the common-mode inductor L5 is connected to the second output terminal of the first EMI filter circuit.

[0010] The first EMI filter circuit also includes a first Y capacitor and a second Y capacitor. One end of the first Y capacitor is connected to the first output terminal of the first EMI filter circuit, and the other end of the first Y capacitor is connected to protective ground. One end of the second Y capacitor is connected to the second output terminal of the first EMI filter circuit, and the other end of the second Y capacitor is connected to protective ground.

[0011] The first EMI filter circuit further includes a first X capacitor and / or a second X capacitor. One end of the first X capacitor is connected to the live wire input terminal of the AC input interface and the first input terminal of the common mode inductor, respectively. The other end of the first X capacitor is connected to the neutral wire input terminal of the AC input interface and the second input terminal of the common mode inductor, respectively. One end of the second X capacitor is connected to the first output terminal of the common mode inductor and the first output terminal of the first EMI filter circuit, respectively. The other end of the second X capacitor is connected to the second output terminal of the common mode inductor and the second output terminal of the first EMI filter circuit, respectively.

[0012] In some embodiments, the AC input pre-stage protection circuit further includes a bypass switch and a PTC resistor connected in series on the live wire of the AC input. The bypass switch is connected in parallel with the PTC resistor and is connected to a switch drive circuit. The input terminal of the switch drive circuit is connected to the output terminal of the undervoltage detection circuit.

[0013] The bypass switch is a relay, and the switch driving circuit includes a transistor V17. The control electrode of the transistor V17 is connected to the output terminal of the undervoltage detection circuit via at least one resistor. The first electrode of the transistor V17 is connected to the first terminal of the relay coil. The second terminal of the relay coil is connected to the power supply voltage via a resistor R30. The second electrode of the transistor V17 is connected to the power ground.

[0014] The switch driving circuit includes one or more of resistor R125, capacitor C112, capacitor C113, and Schottky diode D10. One end of resistor R125, capacitor C112, and capacitor C113 is connected to the control electrode of transistor V17, and the other end of resistor R125, capacitor C112, and capacitor C113 is connected to power ground. The anode of Schottky diode D32 is connected to the control electrode of transistor V17, and the cathode of Schottky diode D32 is connected to one end of resistor R122 and one end of resistor R123. The other end of resistor R122 is connected to the output terminal of the undervoltage detection circuit, and the other end of resistor R123 is connected to the anode of Schottky diode D10 and the control electrode of transistor V17.

[0015] The AC input pre-stage protection circuit also includes a fault output circuit, which includes a transistor V16. The control terminal of transistor V16 is connected to the first terminal of the relay coil and the first terminal of transistor V17 via resistor R120. The first terminal of transistor V16 is the output terminal of the fault output circuit, and the second terminal of transistor V16 is connected to power ground.

[0016] The fault output circuit includes one or more of resistors R124 and capacitors C110. One end of resistor R124 and capacitor C110 is connected to the control electrode of transistor V16, and the other end of resistor R124 and capacitor C110 is connected to power ground.

[0017] In some embodiments, the PFC circuit includes a PFC power main circuit and a PFC control unit. The PFC power main circuit includes a rectifier circuit and a main switch V15. The positive output terminal of the rectifier circuit is connected to the positive terminal of the high-voltage bus via a boost inductor L4 and a freewheeling diode D22. The negative output terminal of the rectifier circuit is connected to the negative terminal of the high-voltage bus. The first terminal of the main switch V15 is connected between the boost inductor L4 and the positive terminal of the freewheeling diode D22. The second terminal of the main switch V15 is connected to the negative terminal of the high-voltage bus and power ground. The control terminal of the main switch V15 is connected to the output terminal of the PFC control unit via a first switch drive circuit.

[0018] The PFC power main circuit also includes a sampling resistor RS1. One end of the sampling resistor RS1 is connected to the negative output terminal of the rectifier circuit and the input terminal of the first current sampling circuit. The other end of the sampling resistor RS1 is connected to the negative terminal of the high voltage bus. The output terminal of the first current sampling circuit is connected to the current sampling input terminal of the LLC control unit.

[0019] The first switching transistor drive circuit includes a resistor R112 and a Schottky diode D30. One end of the resistor R112 is connected to the positive terminal of the Schottky diode D30 and one end of the resistor R114. The other end of the resistor R114 is connected to the control terminal of the main switching transistor V15. The other end of the resistor R112 and the negative terminal of the Schottky diode D30 are connected to the output terminal of the PFC control unit. The control terminal of the main switching transistor V15 is connected to the second terminal of the main switching transistor V15 via a resistor R117.

[0020] The PFC power main circuit also includes at least one of capacitor C105, capacitor C106, and diode D21. One end of capacitor C105 is connected to the positive output terminal of the rectifier circuit, and the other end of capacitor C105 is connected to the negative output terminal of the rectifier circuit. One end of capacitor C106 is connected to the positive terminal of the high-voltage bus, and the other end of capacitor C106 is connected to the negative terminal of the high-voltage bus. The anode of diode D21 is connected to the positive output terminal of the rectifier circuit, and the cathode of diode D21 is connected to the positive terminal of the high-voltage bus.

[0021] In some embodiments, the fault detection circuit includes an undervoltage detection circuit and an overvoltage detection circuit. The output terminal of the undervoltage detection circuit is connected to the first signal output terminal via diode D33, and the output terminal of the overvoltage detection circuit is connected to the first signal output terminal via diode D37. The first signal output terminal is connected to a positive voltage via resistor R127. The first signal output terminal is connected to the second signal output terminal VIN_CTRL via an output filter circuit. The second signal output terminal VIN_CTRL is the output terminal of the fault detection circuit.

[0022] The undervoltage detection circuit includes an operational amplifier N13A. The inverting input terminal of the operational amplifier N13A is connected to a reference voltage via a resistor R129. The non-inverting input terminal of the operational amplifier N13A is connected to the voltage sampling terminal of the undervoltage detection circuit via a resistor R130. The output terminal of the operational amplifier N13A is connected to the non-inverting input terminal of the operational amplifier N13A via a first feedback branch. A feedback resistor R140 and a diode D34 are connected in series in the first feedback branch. The output terminal of the operational amplifier N13A is the output terminal of the undervoltage comparator circuit.

[0023] The overvoltage detection circuit includes an operational amplifier N13B. The inverting input terminal of the operational amplifier N13B is connected to the voltage sampling terminal of the overvoltage detection circuit via a resistor R146. The non-inverting input terminal of the operational amplifier N13B is connected to the reference voltage via a resistor R152. The output terminal of the operational amplifier N13B is connected to the non-inverting input terminal of the operational amplifier N13B via a second feedback branch. A feedback resistor R154 and a diode D38 are connected in series in the second feedback branch. The output terminal of the operational amplifier N13B is the output terminal of the overvoltage comparator circuit.

[0024] The first enable control circuit includes a main switch V19 and a main switch V18. The control terminal of the main switch V19 is connected to the output terminal of the fault detection circuit via a resistor R147. The first terminal of the main switch V19 is connected to the control terminal of the main switch V18 and one end of the resistor R143. The other end of the resistor R143 is connected to a positive voltage. The second terminal of the main switch V19 is connected to power ground. The first terminal of the main switch V18 is connected to the voltage sampling terminal of the PFC control unit. The second terminal of the main switch V18 is connected to power ground. The voltage sampling terminal of the PFC control unit is connected to the output terminal of the first bus voltage sampling circuit. The input terminal of the first bus voltage sampling circuit is connected to the positive terminal of the high-voltage bus.

[0025] The first bus voltage sampling circuit includes a first high-voltage divider network. One end of the first high-voltage divider network is connected to the positive terminal of the high-voltage bus, and the other end of the first high-voltage divider network is connected to the power ground. The voltage division point of the high-voltage divider network is connected to the positive terminal of the high-voltage bus.

[0026] The voltage sampling terminals of the undervoltage detection circuit and the overvoltage detection circuit are both connected to the output terminal of the AC input voltage sampling circuit, and the input terminal of the AC input voltage sampling circuit is connected to the AC input interface.

[0027] The AC input voltage sampling circuit includes a rectifier unit. One input terminal of the rectifier unit is connected to the live wire of the AC input interface via at least one first current-limiting resistor, and the other input terminal of the rectifier unit is connected to the neutral wire of the AC input interface via at least one second current-limiting resistor. The output terminal of the rectifier unit is connected to the input terminal of the filter voltage divider unit, and the output terminal of the filter voltage divider unit is connected to the input terminal of the voltage divider output unit. The output terminal of the voltage divider output unit is the output terminal of the AC input voltage sampling circuit.

[0028] The rectifier unit converts AC to DC. The filter and voltage divider unit filters the rectified high voltage and gradually reduces it. The voltage divider output unit further reduces the voltage after the previous stage and finally outputs the Vs signal. The voltage divider output unit also performs low-pass filtering on the final sampled signal to remove high-frequency noise and ensure the smoothness of the sampled signal.

[0029] In some embodiments, the LLC circuit includes an LLC control unit, a transformer T1, an inductor L1, and main switching transistors V1 and V10. The first terminal of the main switching transistor V1 is connected to the positive terminal of the high-voltage bus. The second terminal of the main switching transistor V1 is connected to the first terminal of the main switching transistor V10, one end of the inductor L1, and the midpoint feedback terminal of the half-bridge of the LLC control unit. The second terminal of the main switching transistor V10 is connected to the negative terminal of the high-voltage bus. The other end of the inductor L1 is connected to one end of the primary winding of the transformer T1. The other end of the primary winding of the transformer T1 is connected to the positive terminal of the high-voltage bus via capacitor C35. The other end of the primary winding of the transformer T1 is connected to the negative terminal of the high-voltage bus via capacitor C44. The other end of the primary winding of the transformer T1 is connected to the anode of diode D2. The cathode of diode D2 is connected to the positive terminal of the high-voltage bus. The other end of the primary winding of the transformer T1 is connected to the cathode of diode D3. The anode of diode D3 is connected to the negative terminal of the high-voltage bus.

[0030] The other end of the primary winding of the transformer T1 is connected to the input terminal of the second current sampling circuit, the output terminal of the second current sampling circuit is connected to the current sampling input terminal of the LLC control unit, the secondary winding of the transformer T1 is connected to the DC output interface through the rectifier circuit, the control electrode of the main switch V1 is connected to the upper tube drive output terminal of the LLC control unit through the second switch drive circuit, and the control electrode of the main switch V10 is connected to the lower tube drive output terminal of the LLC control unit through the third switch drive circuit.

[0031] The second switching transistor drive circuit includes a resistor R9 and a Schottky diode D1. One end of the resistor R9 is connected to the positive terminal of the Schottky diode D1 and the control terminal of the main switching transistor V1. The other end of the resistor R9 and the negative terminal of the Schottky diode D1 are connected to the upper transistor drive output terminal of the LLC control unit. The control terminal of the main switching transistor V1 is connected to the second terminal of the main switching transistor V1 via a resistor R14.

[0032] The third switch drive circuit includes a resistor R21 and a Schottky diode D5. One end of the resistor R21 is connected to the positive terminal of the Schottky diode D5 and the control terminal of the main switch V10. The other end of the resistor R21 and the negative terminal of the Schottky diode D5 are connected to the lower drive output terminal of the LLC control unit. The control terminal of the main switch V10 is connected to the second terminal of the main switch V10 via a resistor R22.

[0033] In some embodiments, the LLC circuit further includes a first voltage monitoring circuit, the input terminal of the first voltage monitoring circuit is connected to the DC output interface, the output terminal of the first voltage monitoring circuit is connected to the input terminal of the first isolation output circuit, the output terminal of the first isolation output circuit is connected to the standby / light load control terminal of the LLC control unit via resistor R61, and the output terminal of the first isolation output circuit is connected to the minimum frequency setting terminal of the LLC control unit via resistor R57.

[0034] The LLC circuit also includes a second voltage monitoring circuit and an external enable input network. The output terminal of the second voltage monitoring circuit is connected to the input terminal of the second isolation output circuit via diode D13. The output terminal of the external enable input network is connected to the input terminal of the second isolation output circuit via diode D14. The output terminal of the second isolation output circuit is connected to the second input terminal of the second enable control circuit.

[0035] The LLC circuit also includes a second bus voltage sampling circuit. The input terminal of the second bus voltage sampling circuit is connected to the positive terminal of the high-voltage bus, and the output terminal of the second bus voltage sampling circuit is connected to the voltage feedback input terminal of the LLC control unit.

[0036] In some embodiments, the first voltage monitoring circuit includes an operational amplifier N3A. The non-inverting input terminal of the operational amplifier N3A is connected to the voltage divider point of a first resistor network via a resistor R41. One end of the first resistor network is connected to the positive terminal of the DC output interface, and the other end of the first resistor network is connected to the negative terminal of the DC output interface. The inverting input terminal of the operational amplifier N3A is connected to a reference voltage via a resistor R36. The output terminal of the operational amplifier N3A is connected to the inverting input terminal of the operational amplifier N3A via a third feedback branch. The output terminal of the operational amplifier N3A is connected to the output terminal of the first voltage monitoring circuit and the input terminal of the first isolation output circuit via a resistor R40. A feedback resistor R35 and a capacitor C53 are connected in series on the third feedback branch.

[0037] And / or,

[0038] The second voltage monitoring circuit includes operational amplifier N3B. The inverting input terminal of operational amplifier N3B is connected to a reference voltage via resistor R67. The non-inverting input terminal of operational amplifier N3B is connected to the voltage divider point of the second resistor network. One end of the second resistor network is connected to the positive terminal of the DC output interface, and the other end of the second resistor network is connected to the negative terminal of the DC output interface. The output terminal of operational amplifier N3B is connected to the non-inverting input terminal of operational amplifier N3B via a fourth feedback branch. The output terminal of operational amplifier N3B is connected to one end of resistor R66 and one end of resistor R59, respectively. The other end of resistor R59 is connected to the positive voltage S_VCC. The other end of resistor R66 is the output terminal of the second voltage monitoring circuit. A feedback resistor R53 and a diode D11 are connected in series in the fourth feedback branch.

[0039] And / or,

[0040] The external enable input network includes resistors R72 and R71. One end of resistor R72 is connected to one end of resistor R71 and the input terminal EN of the external enable input network. The other end of resistor R71 is connected to the positive voltage S_VCC. The other end of resistor R72 is the output terminal of the external enable input network.

[0041] And / or,

[0042] The second bus voltage sampling circuit includes a second high-voltage divider network. One end of the second high-voltage divider network is connected to the positive terminal of the high-voltage bus, and the other end of the second high-voltage divider network is connected to the power ground. The voltage division point of the high-voltage divider network is connected to one end of resistor R58. The other end of resistor R58 is connected to one end of capacitor C64 and the voltage feedback input terminal of the LLC control unit, respectively. The other end of capacitor C64 is connected to the power ground.

[0043] In some embodiments, the second enable control circuit includes a main switch V13 and a main switch V12. The control terminal of the main switch V13 is the first input terminal of the second enable control circuit. The first input terminal of the second enable control circuit is connected to the second input terminal of the second enable control circuit via a resistor R76. The control terminal of the main switch V13 is connected to one end of a resistor R77 and one end of a capacitor C72. The other ends of the resistor R77 and the other ends of the capacitor C72 are connected to power ground PGND. The second terminal of the main switch V13 is connected to power ground PGND. The first terminal of the main switch V13 is connected to one end of a resistor R75 and the control terminal of the main switch V12. The other end of the resistor R75 is connected to the positive voltage P_VCC. The second terminal of the main switch V12 is connected to power ground PGND. The first terminal of the main switch V12 is connected to one end of a resistor R74. The other end of the resistor R74 is the output terminal of the second enable control circuit.

[0044] The rectifier circuit includes a first rectifier tube and a second rectifier tube. One end of the secondary winding of transformer T1 is connected to the positive terminal of the DC output interface through at least one first rectifier tube, and the other end of the secondary winding of transformer T1 is connected to the positive terminal of the DC output interface through at least one second rectifier tube. The common center tap of the secondary winding of transformer T1 is connected to the negative terminal of the DC output interface.

[0045] The rectifier circuit is connected to the DC output interface via a filter circuit and a second EMI filter circuit. A MOS transistor V2 is connected in series between the first output terminal of the second EMI filter circuit and the positive terminal of the DC output interface. The control terminal of the MOS transistor V2 is connected to the MOS transistor driver.

[0046] The LLC circuit further includes at least one of the following: inductor L2, resistor R1, resistor R2, capacitor C19, capacitor C40, capacitor C1, capacitor C7, capacitor C2, capacitor C3, capacitor C6, capacitor C10, capacitor C11, capacitor C12, capacitor C21, capacitor C22, capacitor C23, capacitor C24, capacitor C4, capacitor C26, capacitor C5, and capacitor C28. One end of resistor R1, resistor R2, capacitor C10, capacitor C11, capacitor C12, capacitor C21, capacitor C22, capacitor C23, capacitor C24, capacitor C4, capacitor C26, capacitor C5, capacitor C28, capacitor C2, capacitor C3, and capacitor C6 is connected to the positive terminal of the DC output interface. Resistors R1, R2, C10, C11, C12, and C21 are also connected to the positive terminal of the DC output interface. The other ends of capacitors C22, C23, C24, C4, C26, C5, C28, C2, C3, and C6 are connected to the negative terminal of the DC output interface. One end of capacitor C19 is connected to the positive terminal of the DC output interface, and the other end of capacitor C19 is connected to the protective ground. One end of capacitor C40 is connected to the negative terminal of the DC output interface, and the other end of capacitor C40 is connected to the protective ground. One end of capacitor C1 is connected to the positive terminal of the DC output interface, and the other end of capacitor C1 is connected to the protective ground. One end of capacitor C7 is connected to the negative terminal of the DC output interface, and the other end of capacitor C7 is connected to the protective ground. Inductor L2 has a first winding and a second winding. The first winding of the second inductor L2 is connected in series with the positive terminal of the DC output interface, and the second winding of the inductor L2 is connected in series with the negative terminal of the DC output interface.

[0047] The present invention has at least the following beneficial effects:

[0048] This invention achieves the following technical effects by introducing a fault detection circuit, a first / second enable control circuit, and a bus voltage sampling circuit: In case of a fault, the PFC is forcibly blocked, achieving a "hard shutdown." The fault detection circuit outputs a fault signal, and the first enable control circuit pulls down (or pulls up) the voltage sampling terminal of the PFC control unit. This causes the PFC control unit to mistakenly believe that the bus voltage is abnormal, immediately stopping the PWM output and cutting off the energy input to the high-voltage bus at the source. Simultaneously, the fault signal forces a change in the voltage feedback input terminal of the LLC control unit (e.g., pulling it to a set value) through the second enable control circuit. The LLC control unit will then quickly reduce its switching frequency or shut down directly, preventing fault energy from being transferred to the output terminal. This allows the LLC to dynamically adjust its operating frequency or duty cycle based on the actual bus voltage, especially during the initial stage of bus voltage drop or establishment, preventing overcurrent caused by forced startup under undervoltage conditions.

[0049] The entire fault response is completed by hardware circuits (comparators, logic gates, optocouplers, etc.), without relying on software polling or interrupts. The response time can be controlled in the microsecond range, which is much faster than software protection.

[0050] Enable control is achieved by reusing the existing sampling / feedback pins of PFC and LLC, eliminating the need for additional dedicated enable pins or isolated communication, thus reducing cost and design complexity, while avoiding protection failures caused by communication delays or isolation failures.

[0051] By introducing a simple common-mode noise cancellation unit, this invention can cancel most common-mode noise, thereby allowing the first EMI filter circuit to use a small common-mode inductor with an inductance value that is only 1 / 5 to 1 / 10 of that of conventional solutions, which greatly saves space and magnetic material costs, and significantly reduces volume and cost.

[0052] The entire common-mode noise cancellation unit of this invention uses only one operational amplifier and a small number of resistors and capacitors, eliminating the need for complex control loops and independent power supplies. The circuit structure is simple, the cost is low, and the reliability is high.

[0053] Traditional passive filters fail at high frequencies due to parasitic parameters, while the common-mode noise cancellation unit of this invention can still maintain good cancellation effect in the frequency band from hundreds of kHz to tens of MHz, making up for the high-frequency shortcomings of passive filters and providing good high-frequency suppression.

[0054] The EMI filter circuit of this invention has a simple structure and is very easy to integrate with existing switching power supply control chips to form a single-chip solution, which has good prospects for industrial application. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1 A schematic diagram of a PFC-LLC resonant switching power supply provided in an embodiment of the present invention;

[0057] Figure 2 A schematic diagram of the AC input pre-stage protection circuit provided in an embodiment of the present invention;

[0058] Figure 3 A schematic diagram of a PFC circuit provided in an embodiment of the present invention;

[0059] Figure 4 A schematic diagram of a fault detection circuit provided in an embodiment of the present invention;

[0060] Figure 5 This is a schematic diagram of a common-mode noise cancellation unit provided in an embodiment of the present invention;

[0061] Figure 6 A schematic diagram of an LLC circuit provided in an embodiment of the present invention;

[0062] Figure 7 A schematic diagram of an LLC control unit provided in an embodiment of the present invention;

[0063] Figure 8 A schematic diagram of a first voltage monitoring circuit and a second voltage monitoring circuit provided in an embodiment of the present invention;

[0064] Figure 9 This is a schematic diagram of an isolated power supply circuit provided in an embodiment of the present invention. Detailed Implementation

[0065] To enable those skilled in the art to better understand the technical solutions of the present invention, exemplary embodiments of the present invention are described below in conjunction with the accompanying drawings, including various details of the embodiments of the present invention to aid understanding. These should be considered merely exemplary. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0066] Where there is no conflict, the various embodiments of the present invention and the features thereof may be combined with each other.

[0067] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0068] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms “a” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “made of” are used in this specification, the presence of the stated feature, integral, step, operation, element, and / or component is specified, but the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof is not excluded. Terms such as “connected” or “linked” are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect.

[0069] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having the meaning consistent with their meaning in the context of the relevant art and the invention, and will not be interpreted as having an idealized or overly formal meaning unless expressly so defined herein.

[0070] See Figures 1 to 8 This invention discloses a PFC-LLC resonant switching power supply, including a PFC circuit and an LLC circuit. The input terminal of the PFC circuit is connected to an AC input interface, and the output terminal of the PFC circuit is connected to the input terminal of the LLC circuit via a high-voltage bus. The output terminal of the LLC circuit is connected to a DC output interface. The power supply also includes a bus voltage sampling circuit, a fault detection circuit, a first enable control circuit, and a second enable control circuit. The input terminal of the first enable control circuit is connected to the output terminal of the fault detection circuit, and its output terminal is connected to the voltage sampling terminal of the PFC control unit of the PFC circuit. The first input terminal of the second enable control circuit is connected to the output terminal of the fault detection circuit, and its output terminal is connected to the voltage feedback input terminal of the LLC control unit of the LLC circuit. The input terminal of the bus voltage sampling circuit is connected to the input terminal of the LLC circuit, and its output terminal is connected to the voltage feedback input terminal of the LLC control unit.

[0071] In some embodiments, an AC input pre-stage protection circuit is provided between the input terminal of the PFC circuit and the AC input interface. The AC input pre-stage protection circuit includes a first EMI filter circuit and a common-mode noise cancellation unit. The common-mode noise cancellation unit includes a sampling network, an operational amplifier, and an injection capacitor. The input terminal of the first EMI filter circuit is connected to the AC input interface. One end of the sampling network is connected to the first output terminal of the first EMI filter circuit, and the other end of the sampling network is connected to the second output terminal of the first EMI filter circuit. The sampling output point of the sampling network is connected to one input terminal of the operational amplifier. The output terminal of the operational amplifier is connected to one end of the injection capacitor, and the other end of the injection capacitor is connected to protective ground.

[0072] In some embodiments, the output of the operational amplifier may also be connected to the control unit of the PFC circuit.

[0073] In some embodiments, the first EMI filter circuit includes a common-mode inductor L5, the first input terminal of which is connected to the live wire input terminal of the AC input interface, the second input terminal of which is connected to the neutral wire input terminal of the AC input interface, the first output terminal of which is connected to the first output terminal of the first EMI filter circuit, and the second output terminal of which is connected to the second output terminal of the first EMI filter circuit.

[0074] The common-mode inductor L5 is a small-value common-mode inductor, i.e., a miniature common-mode inductor. In some embodiments, the inductance value of the common-mode inductor L5 can be selected as 1 / 5 of the conventional design value. For example, for a 100W power supply, a conventional common-mode inductor may require 10mH, while in this invention, 2mH or even less can be selected.

[0075] The first EMI filter circuit also includes a first Y capacitor and a second Y capacitor. One end of the first Y capacitor is connected to the first output terminal of the first EMI filter circuit, and the other end of the first Y capacitor is connected to protective ground. One end of the second Y capacitor is connected to the second output terminal of the first EMI filter circuit, and the other end of the second Y capacitor is connected to protective ground.

[0076] The first EMI filter circuit further includes a first X capacitor and / or a second X capacitor. One end of the first X capacitor is connected to the live wire input terminal of the AC input interface and the first input terminal of the common mode inductor, respectively. The other end of the first X capacitor is connected to the neutral wire input terminal of the AC input interface and the second input terminal of the common mode inductor, respectively. One end of the second X capacitor is connected to the first output terminal of the common mode inductor and the first output terminal of the first EMI filter circuit, respectively. The other end of the second X capacitor is connected to the second output terminal of the common mode inductor and the second output terminal of the first EMI filter circuit, respectively.

[0077] In some embodiments, the first input terminal of the operational amplifier U1 is connected to the sampling output point of the sampling network via a DC blocking capacitor C201.

[0078] In some embodiments, the sampling network includes resistors R201 and R202. One end of resistor R201 is connected to the first output terminal of the first EMI filter circuit, and the other end of resistor R201 is connected to one end of resistor R202 and the sampling output point, respectively. The other end of resistor R202 is connected to the second output terminal of the first EMI filter circuit.

[0079] The sampling network consists of two high-resistance resistors, R201 and R202, connected in series across the power input lines to sample common-mode noise in the form of differential-mode voltage.

[0080] In some embodiments, the non-inverting input of operational amplifier U1 is connected to the sampling output point of the sampling network, the inverting input of operational amplifier U1 is connected to one end of resistor R203 and one end of resistor R204 respectively, the other end of resistor R203 is grounded, and the other end of resistor R204 is connected to the output of operational amplifier U1.

[0081] The non-inverting input of operational amplifier U1 is connected to the midpoint of the sampling network (i.e., the connection point of R201 and R202) through capacitor C201. The inverting input of operational amplifier U1 is grounded through resistor R203 and connected to the output through resistor R204. The power supply for operational amplifier U1 is provided by the auxiliary winding in the main circuit of the switching power supply after simple rectification.

[0082] This invention is a compact EMI filter circuit based on active common-mode noise cancellation, used to connect between the power input line and the main circuit of the switching power supply.

[0083] The common-mode noise cancellation unit operates as follows:

[0084] Noise Sampling: The common-mode noise current generated by the main circuit of the switching power supply flows through the L and N lines. Since the common-mode noise on the L and N lines is in phase, it is converted into a differential-mode voltage signal across resistors R201 and R202. The midpoint of this voltage signal, i.e., the connection point of R201 and R202, contains the voltage information of the common-mode noise.

[0085] Signal Processing: The common-mode noise voltage is coupled to the non-inverting input of operational amplifier U1 through DC blocking capacitor C201. U1 and its peripheral components R203 and R204 constitute a non-inverting amplifier circuit, whose gain Av is determined by Av = 1 + (R204 / R203). By properly setting the resistance values ​​of R203 and R204, the gain Av can be approximately equal to 1 or slightly greater than 1. More importantly, this circuit acts as a buffer and driver.

[0086] Noise cancellation: The signal amplified / buffered by U1 has the same phase as the original sampled common-mode noise voltage. Injection capacitor C202 is connected between the output of operational amplifier U1 and safety ground.

[0087] This voltage, through the injection capacitor C202, generates an injection current that is out of phase with the original common-mode noise current on the power line. This reverse current flows into the safety ground through C202, thus forming a canceling current on the L and N lines that is similar in magnitude but opposite in direction to the original noise current, effectively neutralizing the common-mode noise conducted to the power grid.

[0088] This invention introduces a simple active cancellation unit, which can cancel most common-mode noise, allowing the use of a small common-mode inductor with an inductance value only 1 / 5 to 1 / 10 of that in traditional solutions, greatly saving space and magnetic material costs. The entire cancellation unit uses only one operational amplifier and a few resistor-capacitor components, eliminating the need for complex control loops and independent power supplies, resulting in a simple structure, low cost, and high reliability. Traditional passive filters fail at high frequencies due to parasitic parameters, while the cancellation circuit of this invention maintains good cancellation performance in the frequency range of hundreds of kHz to tens of MHz, compensating for the high-frequency limitations of passive filters.

[0089] Using the 100W power supply of the circuit in this embodiment, in conducted EMI testing, the noise margin is improved by an average of more than 10dB in the frequency band from 150kHz to 30MHz compared to the solution using a conventional 10mH passive filter, especially in the high-frequency band above 1MHz, where the improvement is more obvious.

[0090] The EMI filter circuit of this invention has a simple structure and is very easy to integrate with existing switching power supply control chips to form a single-chip solution, which has good prospects for industrial application.

[0091] In some embodiments, the AC input pre-stage protection circuit further includes a bypass switch and a PTC resistor R108 connected in series on the live wire of the AC input. The bypass switch is connected in parallel with the PTC resistor R108. The bypass switch is connected to a switch drive circuit, and the input terminal of the switch drive circuit is connected to the output terminal of the undervoltage detection circuit.

[0092] The bypass switch is a relay, and the switch driving circuit includes a transistor V17. The control electrode of the transistor V17 is connected to the output terminal of the undervoltage detection circuit via at least one resistor. The first electrode of the transistor V17 is connected to the first terminal of the relay coil. The second terminal of the relay coil is connected to the power supply voltage via a resistor R30. The second electrode of the transistor V17 is connected to the power ground.

[0093] In some embodiments, the AC input pre-stage protection circuit of the present invention further includes one or more of a varistor MOV1 and a fuse, wherein the fuse is connected in series with the live wire of the AC input, one end of the varistor MOV1 is connected to the live wire of the AC input, and the other end of the varistor MOV1 is connected to the neutral wire of the AC input, and the EMI filter network is located at the rear end of the PTC resistor.

[0094] Fuse FU1 is located before the PTC resistor. Varistor MOV1 is located before the PTC resistor.

[0095] After the AC input passes through the first EMI filter circuit, residual noise is filtered out, and a clean AC signal is output to the subsequent rectifier / PFC circuit.

[0096] The line protection unit consists of fuse FU1, varistor and resettable fuse R84, to achieve overcurrent and surge protection.

[0097] A varistor, connected in parallel between ACL and ACN, absorbs overvoltages from lightning strikes / power grid surges, protecting downstream circuits.

[0098] The switch driving circuit includes one or more of resistor R125, capacitor C112, capacitor C113, and Schottky diode D10. One end of resistor R125, capacitor C112, and capacitor C113 is connected to the control electrode of transistor V17, and the other end of resistor R125, capacitor C112, and capacitor C113 is connected to power ground. The anode of Schottky diode D32 is connected to the control electrode of transistor V17, and the cathode of Schottky diode D32 is connected to one end of resistor R122 and one end of resistor R123. The other end of resistor R122 is connected to the output terminal of the undervoltage detection circuit, and the other end of resistor R123 is connected to the anode of Schottky diode D10 and the control electrode of transistor V17.

[0099] The AC input pre-stage protection circuit also includes a fault output circuit, which includes a transistor V16. The control terminal of transistor V16 is connected to the first terminal of the relay coil and the first terminal of transistor V17 via resistor R120. The first terminal of transistor V16 is the output terminal of the fault output circuit, and the second terminal of transistor V16 is connected to power ground.

[0100] The fault output circuit includes one or more of resistors R124 and capacitors C110. One end of resistor R124 and capacitor C110 is connected to the control electrode of transistor V16, and the other end of resistor R124 and capacitor C110 is connected to power ground.

[0101] The protection circuit detects overvoltage / undervoltage conditions of the input voltage (Vx); outputs a fault signal (VIN_FAULT) to indicate voltage abnormality; and outputs a control signal (VIN_CTRL) to actively adjust the front-end power supply (e.g., shutting down the input or adjusting DC-DC parameters). This protection circuit prevents damage to downstream circuits due to excessively high / low input voltage, reduces false triggering of protection circuits caused by power supply noise, and achieves closed-loop protection of "detection + control." Compared to circuits that only output fault signals, this provides more proactive protection. The use of general-purpose components (LM2904 op-amp, MA431 reference) reduces costs while ensuring detection accuracy.

[0102] This application implements a closed-loop protection system of "voltage detection + fault reporting + active control." The output VIN_CTRL signal can directly link the front-end relay to cut off the mains power and adjust the operating parameters of the subsequent DC-DC converter. Active protection can be achieved without the need for MCU relay, significantly improving fault response speed and protection reliability. This application uses diode "OR" logic to achieve unified reporting of multiple fault signals, and can directly expand to include other fault signals such as overvoltage and overcurrent. All fault states can be fed back to the main controller through a single VIN_FAULT signal, simplifying the signal processing logic of the subsequent MCU and improving the scalability of the circuit.

[0103] In some embodiments, the PFC circuit includes a PFC power main circuit and a PFC control unit. The PFC power main circuit includes a rectifier circuit and a main switch V15. The positive output terminal of the rectifier circuit is connected to the positive terminal of the high-voltage bus via a boost inductor L4 and a freewheeling diode D22. The negative output terminal of the rectifier circuit is connected to the negative terminal of the high-voltage bus. The first terminal of the main switch V15 is connected between the boost inductor L4 and the positive terminal of the freewheeling diode D22. The second terminal of the main switch V15 is connected to the negative terminal of the high-voltage bus and power ground. The control terminal of the main switch V15 is connected to the output terminal of the PFC control unit via a first switch drive circuit.

[0104] In some embodiments, the rectifier circuit is a bridge rectifier circuit.

[0105] In some embodiments, the AC input terminal of the rectifier circuit of the PFC power main circuit is connected to the AC input interface via an AC input pre-stage protection circuit.

[0106] The PFC power main circuit also includes a sampling resistor RS1. One end of the sampling resistor RS1 is connected to the negative output terminal of the rectifier circuit and the input terminal of the first current sampling circuit. The other end of the sampling resistor RS1 is connected to the negative terminal of the high voltage bus. The output terminal of the first current sampling circuit is connected to the current sampling input terminal of the LLC control unit.

[0107] The first current sampling circuit includes a resistor R92, a capacitor C34, and a clamping diode D29. One end of the resistor R92 is connected to one end of the sampling resistor RS1. The other end of the resistor R92 is connected to one end of the capacitor C34, one end of the clamping diode D29, and the current sampling input terminal of the LLC control unit. The other ends of the capacitor C34 and the clamping diode D29 are connected to power ground.

[0108] D29 clamps voltage spikes to prevent overvoltage damage to the controller; C34 filters out high-frequency interference to ensure the accuracy of the sampled signal. This clamping filter network improves the reliability and anti-interference capability of overcurrent protection.

[0109] The first switching transistor drive circuit includes a resistor R112 and a Schottky diode D30. One end of the resistor R112 is connected to the positive terminal of the Schottky diode D30 and one end of the resistor R114. The other end of the resistor R114 is connected to the control terminal of the main switching transistor V15. The other end of the resistor R112 and the negative terminal of the Schottky diode D30 are connected to the output terminal of the PFC control unit. The control terminal of the main switching transistor V15 is connected to the second terminal of the main switching transistor V15 via a resistor R117.

[0110] The PFC power main circuit also includes at least one of capacitor C105, capacitor C106, and diode D21. One end of capacitor C105 is connected to the positive output terminal of the rectifier circuit, and the other end of capacitor C105 is connected to the negative output terminal of the rectifier circuit. One end of capacitor C106 is connected to the positive terminal of the high-voltage bus, and the other end of capacitor C106 is connected to the negative terminal of the high-voltage bus. The anode of diode D21 is connected to the positive output terminal of the rectifier circuit, and the cathode of diode D21 is connected to the positive terminal of the high-voltage bus.

[0111] In some embodiments, the fault detection circuit includes an undervoltage detection circuit and an overvoltage detection circuit. The output terminal of the undervoltage detection circuit is connected to the first signal output terminal via diode D33, and the output terminal of the overvoltage detection circuit is connected to the first signal output terminal via diode D37. The first signal output terminal is connected to a positive voltage via resistor R127. The first signal output terminal is connected to the second signal output terminal VIN_CTRL via an output filter circuit. The second signal output terminal VIN_CTRL is the output terminal of the fault detection circuit.

[0112] The output filter circuit is an RC low-pass filter circuit, which includes a resistor R150 and a capacitor C124. One end of the resistor R150 is connected to the first signal output terminal VIN_FAULT via a diode D12. The other end of the resistor R150 is connected to the second signal output terminal VIN_CTRL and one end of the capacitor C124. The other end of the capacitor C124 is connected to power ground.

[0113] In some embodiments, the undervoltage detection circuit includes an operational amplifier N13A. The inverting input terminal of the operational amplifier N13A is connected to a reference voltage via a resistor R129. The non-inverting input terminal of the operational amplifier N13A is connected to the voltage sampling terminal of the undervoltage detection circuit via a resistor R130. The output terminal of the operational amplifier N13A is connected to the non-inverting input terminal of the operational amplifier N13A via a first feedback branch. A feedback resistor R140 and a diode D34 are connected in series on the first feedback branch. The output terminal of the operational amplifier N13A is the output terminal of the undervoltage comparator circuit.

[0114] In some embodiments, the positive terminal of diode D34 is connected to the non-inverting input terminal of operational amplifier N13A via feedback resistor R140, and the negative terminal of diode D34 is connected to the output terminal of operational amplifier N13A.

[0115] The undervoltage detection circuit further includes one or more of resistor R133, capacitor C116, capacitor C117, and capacitor C114. One end of resistor R133 is connected to the inverting input terminal of operational amplifier N13A, and the other end of resistor R133 is connected to power ground. One end of capacitor C117 is connected to the inverting input terminal of operational amplifier N13A, and the other end of capacitor C117 is connected to power ground. One end of capacitor C116 is connected to the non-inverting input terminal of operational amplifier N13A, and the other end of capacitor C116 is connected to power ground. One end of capacitor C114 is connected to the output terminal of operational amplifier N13A, and the other end of capacitor C114 is connected to power ground.

[0116] In some embodiments, the overvoltage detection circuit includes an operational amplifier N13B. The inverting input terminal of the operational amplifier N13B is connected to the voltage sampling terminal of the overvoltage detection circuit via a resistor R146. The non-inverting input terminal of the operational amplifier N13B is connected to a reference voltage via a resistor R152. The output terminal of the operational amplifier N13B is connected to the non-inverting input terminal of the operational amplifier N13B via a second feedback branch. A feedback resistor R154 and a diode D38 are connected in series in the second feedback branch. The output terminal of the operational amplifier N13B is the output terminal of the overvoltage comparator circuit.

[0117] In some embodiments, the positive terminal of diode D38 is connected to the non-inverting input terminal of operational amplifier N13B via feedback resistor R154, and the negative terminal of diode D38 is connected to the output terminal of operational amplifier N13B.

[0118] In some embodiments, the overvoltage detection circuit of the present invention further includes one or more of resistor R153, capacitor C125, capacitor C126, and capacitor C123. One end of resistor R153 is connected to the non-inverting input terminal of operational amplifier N13B, and the other end of resistor R153 is connected to power ground. One end of capacitor C125 is connected to the non-inverting input terminal of operational amplifier N13B, and the other end of capacitor C125 is connected to power ground. One end of capacitor C126 is connected to the inverting input terminal of operational amplifier N13B, and the other end of capacitor C126 is connected to power ground. One end of capacitor C123 is connected to the output terminal of operational amplifier N13B, and the other end of capacitor C123 is connected to power ground.

[0119] In some embodiments, the fault detection circuit further includes an over-temperature detection circuit, the output of which is connected to the first signal output via diode D39.

[0120] In some embodiments, the over-temperature detection circuit includes a temperature sampling circuit and an operational amplifier N15. The inverting input terminal of the operational amplifier N15 is connected to a reference voltage, the non-inverting input terminal of the operational amplifier N15 is connected to the temperature sampling circuit, the output terminal of the operational amplifier N15 is connected to the non-inverting input terminal of the operational amplifier N15 via a resistor R156, the output terminal of the operational amplifier N15 is connected to a positive voltage via a resistor R157, and the output terminal of the operational amplifier N15 is the output terminal of the over-temperature detection circuit.

[0121] The temperature sampling circuit includes a thermistor. One end of the thermistor is connected to power ground, and the other end of the thermistor is connected to one end of the voltage divider resistor R159 and the non-inverting input of the operational amplifier N15. The other end of the voltage divider resistor R159 is connected to a positive voltage.

[0122] The over-temperature detection circuit also includes capacitor C128. One end of capacitor C128 is connected to the non-inverting input of op-amp N15, and the other end of capacitor C128 is connected to power ground.

[0123] The over-temperature detection circuit also includes resistors R162 and R160. One end of resistor R162 is connected to one end of resistor R160 and the inverting input of operational amplifier N15, respectively. The other end of resistor R162 is connected to power ground, and the other end of resistor R160 is connected to a positive voltage.

[0124] The over-temperature detection circuit also includes capacitor C129. One end of capacitor C129 is connected to the inverting input of operational amplifier N15, and the other end of capacitor C129 is connected to power ground.

[0125] The over-temperature detection circuit also includes a resistor R163. One end of the resistor R163 is connected to the inverting input of the operational amplifier N15, and the other end of the resistor R163 is connected to power ground.

[0126] In some embodiments, the first enable control circuit includes a main switch V19 and a main switch V18. The control terminal of the main switch V19 is connected to the output terminal of the fault detection circuit via a resistor R147. The first terminal of the main switch V19 is connected to the control terminal of the main switch V18 and one end of the resistor R143. The other end of the resistor R143 is connected to a positive voltage. The second terminal of the main switch V19 is connected to power ground. The first terminal of the main switch V18 is connected to the voltage sampling terminal of the PFC control unit. The second terminal of the main switch V18 is connected to power ground. The voltage sampling terminal of the PFC control unit is connected to the output terminal of the first bus voltage sampling circuit. The input terminal of the first bus voltage sampling circuit is connected to the positive terminal of the high-voltage bus.

[0127] The first enable control circuit also includes a resistor R151 and / or a capacitor C122. One end of the resistor R151 is connected to the control electrode of the main switch V19, and the other end of the resistor R151 is connected to power ground. One end of the capacitor C122 is connected to the control electrode of the main switch V19, and the other end of the capacitor C122 is connected to power ground.

[0128] The first bus voltage sampling circuit includes a first high-voltage divider network. One end of the first high-voltage divider network is connected to the positive terminal of the high-voltage bus, and the other end of the first high-voltage divider network is connected to the power ground. The voltage division point of the high-voltage divider network is connected to the positive terminal of the high-voltage bus.

[0129] The voltage sampling terminals of the undervoltage detection circuit and the overvoltage detection circuit are both connected to the output terminal of the AC input voltage sampling circuit, and the input terminal of the AC input voltage sampling circuit is connected to the AC input interface.

[0130] The AC input voltage sampling circuit includes a rectifier unit. One input terminal of the rectifier unit is connected to the live wire of the AC input interface via at least one first current-limiting resistor, and the other input terminal of the rectifier unit is connected to the neutral wire of the AC input interface via at least one second current-limiting resistor. The output terminal of the rectifier unit is connected to the input terminal of the filter voltage divider unit, and the output terminal of the filter voltage divider unit is connected to the input terminal of the voltage divider output unit. The output terminal of the voltage divider output unit is the output terminal of the AC input voltage sampling circuit.

[0131] The rectifier unit converts AC to DC. The filter and voltage divider unit filters the rectified high voltage and gradually reduces it. The voltage divider output unit further reduces the voltage after the previous stage and finally outputs the Vs signal. The voltage divider output unit also performs low-pass filtering on the final sampled signal to remove high-frequency noise and ensure the smoothness of the sampled signal.

[0132] This invention adds an independent hardware protection link, no longer relying solely on the internal protection of the PFC control unit. When overvoltage or other faults occur, it can actively intervene in the sampling loop, ensuring reliable protection even if the chip or system logic malfunctions, thus improving the overall fault protection redundancy. Furthermore, the first enable control circuit acts as an intermediate isolation buffer unit, isolating the high-voltage sampling node from the low-voltage fault detection signal, preventing high-voltage spikes and switching noise from flowing back to the front-end fault detection circuit, preventing damage to low-voltage control devices, and enhancing the circuit's EMC anti-interference performance.

[0133] In some embodiments, the LLC circuit includes an LLC control unit, a transformer T1, an inductor L1, and main switching transistors V1 and V10. The first terminal of the main switching transistor V1 is connected to the positive terminal of the high-voltage bus. The second terminal of the main switching transistor V1 is connected to the first terminal of the main switching transistor V10, one end of the inductor L1, and the midpoint feedback terminal of the half-bridge of the LLC control unit. The second terminal of the main switching transistor V10 is connected to the negative terminal of the high-voltage bus. The other end of the inductor L1 is connected to one end of the primary winding of the transformer T1. The other end of the primary winding of the transformer T1 is connected to the positive terminal of the high-voltage bus via capacitor C35. The other end of the primary winding of the transformer T1 is connected to the negative terminal of the high-voltage bus via capacitor C44. The other end of the primary winding of the transformer T1 is connected to the anode of diode D2. The cathode of diode D2 is connected to the positive terminal of the high-voltage bus. The other end of the primary winding of the transformer T1 is connected to the cathode of diode D3. The anode of diode D3 is connected to the negative terminal of the high-voltage bus.

[0134] The other end of the primary winding of the transformer T1 is connected to the input terminal of the second current sampling circuit, the output terminal of the second current sampling circuit is connected to the current sampling input terminal of the LLC control unit, the secondary winding of the transformer T1 is connected to the DC output interface through the rectifier circuit, the control electrode of the main switch V1 is connected to the upper tube drive output terminal of the LLC control unit through the second switch drive circuit, and the control electrode of the main switch V10 is connected to the lower tube drive output terminal of the LLC control unit through the third switch drive circuit.

[0135] The second switching transistor drive circuit includes a resistor R9 and a Schottky diode D1. One end of the resistor R9 is connected to the positive terminal of the Schottky diode D1 and the control terminal of the main switching transistor V1. The other end of the resistor R9 and the negative terminal of the Schottky diode D1 are connected to the upper transistor drive output terminal of the LLC control unit. The control terminal of the main switching transistor V1 is connected to the second terminal of the main switching transistor V1 via a resistor R14.

[0136] The third switch drive circuit includes a resistor R21 and a Schottky diode D5. One end of the resistor R21 is connected to the positive terminal of the Schottky diode D5 and the control terminal of the main switch V10. The other end of the resistor R21 and the negative terminal of the Schottky diode D5 are connected to the lower drive output terminal of the LLC control unit. The control terminal of the main switch V10 is connected to the second terminal of the main switch V10 via a resistor R22.

[0137] In some embodiments, the LLC circuit further includes a first voltage monitoring circuit, the input terminal of the first voltage monitoring circuit is connected to the DC output interface, the output terminal of the first voltage monitoring circuit is connected to the input terminal of the first isolation output circuit, the output terminal of the first isolation output circuit is connected to the standby / light load control terminal of the LLC control unit via resistor R61, and the output terminal of the first isolation output circuit is connected to the minimum frequency setting terminal of the LLC control unit via resistor R57.

[0138] The LLC circuit also includes a second voltage monitoring circuit and an external enable input network. The output terminal of the second voltage monitoring circuit is connected to the input terminal of the second isolation output circuit via diode D13. The output terminal of the external enable input network is connected to the input terminal of the second isolation output circuit via diode D14. The output terminal of the second isolation output circuit is connected to the second input terminal of the second enable control circuit.

[0139] The LLC circuit also includes a second bus voltage sampling circuit. The input terminal of the second bus voltage sampling circuit is connected to the positive terminal of the high-voltage bus, and the output terminal of the second bus voltage sampling circuit is connected to the voltage feedback input terminal of the LLC control unit.

[0140] In some embodiments, the first isolated output circuit and the first isolated output circuit adopt optocoupler isolation circuit.

[0141] In some embodiments, the optocoupler isolation circuit includes an optocoupler N4. The anode of the light-emitting diode of the optocoupler N4 is connected to one end of the resistor R42 and the input terminal of the optocoupler isolation circuit, respectively. The other end of the resistor R42 and the cathode of the light-emitting diode of the optocoupler N4 are connected to the signal ground 24V_SGND. The collector of the phototransistor of the optocoupler N4 is connected to the output terminal of the optocoupler isolation circuit, and the emitter of the phototransistor of the optocoupler N4 is connected to the power ground.

[0142] In some embodiments, the first voltage monitoring circuit includes an operational amplifier N3A. The non-inverting input terminal of the operational amplifier N3A is connected to the voltage divider point of a first resistor network via a resistor R41. One end of the first resistor network is connected to the positive terminal of the DC output interface, and the other end of the first resistor network is connected to the negative terminal of the DC output interface. The inverting input terminal of the operational amplifier N3A is connected to a reference voltage via a resistor R36. The output terminal of the operational amplifier N3A is connected to the inverting input terminal of the operational amplifier N3A via a third feedback branch. The output terminal of the operational amplifier N3A is connected to the output terminal of the first voltage monitoring circuit and the input terminal of the first isolation output circuit via a resistor R40. A feedback resistor R35 and a capacitor C53 are connected in series on the third feedback branch.

[0143] In some embodiments, the second voltage monitoring circuit includes an operational amplifier N3B. The inverting input terminal of the operational amplifier N3B is connected to a reference voltage via a resistor R67. The non-inverting input terminal of the operational amplifier N3B is connected to the voltage divider point of a second resistor network. One end of the second resistor network is connected to the positive terminal of the DC output interface, and the other end of the second resistor network is connected to the negative terminal of the DC output interface. The output terminal of the operational amplifier N3B is connected to the non-inverting input terminal of the operational amplifier N3B via a fourth feedback branch. The output terminal of the operational amplifier N3B is connected to one end of a resistor R66 and one end of a resistor R59, respectively. The other end of the resistor R59 is connected to the positive voltage S_VCC. The other end of the resistor R66 is the output terminal of the second voltage monitoring circuit. A feedback resistor R53 and a diode D11 are connected in series on the fourth feedback branch.

[0144] In some embodiments, the external enable input network includes resistors R72 and R71. One end of resistor R72 is connected to one end of resistor R71 and the input terminal EN of the external enable input network, respectively. The other end of resistor R71 is connected to the positive voltage S_VCC, and the other end of resistor R72 is the output terminal of the external enable input network.

[0145] In some embodiments, the second bus voltage sampling circuit includes a second high-voltage divider network. One end of the second high-voltage divider network is connected to the positive terminal of the high-voltage bus, and the other end of the second high-voltage divider network is connected to power ground. The voltage division point of the high-voltage divider network is connected to one end of resistor R58. The other end of resistor R58 is connected to one end of capacitor C64 and the voltage feedback input terminal of the LLC control unit, respectively. The other end of capacitor C64 is connected to power ground.

[0146] In some embodiments, the second enable control circuit includes a main switch V13 and a main switch V12. The control terminal of the main switch V13 is the first input terminal of the second enable control circuit. The first input terminal of the second enable control circuit is connected to the second input terminal of the second enable control circuit via a resistor R76. The control terminal of the main switch V13 is connected to one end of a resistor R77 and one end of a capacitor C72. The other ends of the resistor R77 and the other ends of the capacitor C72 are connected to power ground PGND. The second terminal of the main switch V13 is connected to power ground PGND. The first terminal of the main switch V13 is connected to one end of a resistor R75 and the control terminal of the main switch V12. The other end of the resistor R75 is connected to the positive voltage P_VCC. The second terminal of the main switch V12 is connected to power ground PGND. The first terminal of the main switch V12 is connected to one end of a resistor R74. The other end of the resistor R74 is the output terminal of the second enable control circuit.

[0147] The rectifier circuit includes a first rectifier tube and a second rectifier tube. One end of the secondary winding of transformer T1 is connected to the positive terminal of the DC output interface through at least one first rectifier tube, and the other end of the secondary winding of transformer T1 is connected to the positive terminal of the DC output interface through at least one second rectifier tube. The common center tap of the secondary winding of transformer T1 is connected to the negative terminal of the DC output interface.

[0148] The rectifier circuit is connected to the DC output interface via a filter circuit and a second EMI filter circuit. A MOS transistor V2 is connected in series between the first output terminal of the second EMI filter circuit and the positive terminal of the DC output interface. The control terminal of the MOS transistor V2 is connected to the MOS transistor driver.

[0149] The LLC circuit further includes at least one of the following: inductor L2, resistor R1, resistor R2, capacitor C19, capacitor C40, capacitor C1, capacitor C7, capacitor C2, capacitor C3, capacitor C6, capacitor C10, capacitor C11, capacitor C12, capacitor C21, capacitor C22, capacitor C23, capacitor C24, capacitor C4, capacitor C26, capacitor C5, and capacitor C28. One end of resistor R1, resistor R2, capacitor C10, capacitor C11, capacitor C12, capacitor C21, capacitor C22, capacitor C23, capacitor C24, capacitor C4, capacitor C26, capacitor C5, capacitor C28, capacitor C2, capacitor C3, and capacitor C6 is connected to the positive terminal of the DC output interface. Resistors R1, R2, C10, C11, C12, and C21 are also connected to the positive terminal of the DC output interface. The other ends of capacitors C22, C23, C24, C4, C26, C5, C28, C2, C3, and C6 are connected to the negative terminal of the DC output interface. One end of capacitor C19 is connected to the positive terminal of the DC output interface, and the other end of capacitor C19 is connected to the protective ground. One end of capacitor C40 is connected to the negative terminal of the DC output interface, and the other end of capacitor C40 is connected to the protective ground. One end of capacitor C1 is connected to the positive terminal of the DC output interface, and the other end of capacitor C1 is connected to the protective ground. One end of capacitor C7 is connected to the negative terminal of the DC output interface, and the other end of capacitor C7 is connected to the protective ground. Inductor L2 has a first winding and a second winding. The first winding of the second inductor L2 is connected in series with the positive terminal of the DC output interface, and the second winding of the inductor L2 is connected in series with the negative terminal of the DC output interface.

[0150] In some embodiments, the MOSFET driver includes an ideal diode controller N1. The gate drive output pin of the ideal diode controller N1 is connected to the control electrode of the MOSFET V2 via resistor R7. The output voltage sampling pin of the ideal diode controller N1 is connected to the second electrode of the MOSFET V2 via resistor R8. The output voltage sampling pin of the ideal diode controller N1 is connected to one end of resistor R12. The other end of resistor R12 is connected to the VS pin of the ideal diode controller N1 and one end of capacitor C17. The other end of capacitor C17 is connected to the negative terminal of the DC output interface. The IN pin of the ideal diode controller N1 is connected to the first electrode of the MOSFET V2.

[0151] In some embodiments, the PFC-LLC resonant switching power supply of the present invention further includes an isolation power supply circuit, which is used to supply power to the PFC-LLC resonant switching power supply, such as providing P_VCC and S_VCC. P_VCC is used to supply power to the high-voltage side circuit, and S_VCC is used to supply power to the low-voltage side circuit.

[0152] See Figure 9The isolated power supply circuit includes a PWM master control chip, an isolation transformer, an isolation feedback circuit, and a switching transistor V11. The isolation transformer includes a transformer core and a first primary winding, a second primary winding, and / or a first secondary winding wound on the transformer core. One end of the first primary winding is connected to the positive terminal HVDC of the high-voltage bus, and the other end is connected to the first terminal of the switching transistor V11. The second terminal of the switching transistor V11 is directly or via a resistor connected to the primary power ground PGND. The control terminal of the switching transistor V11 is connected to the drive input of the PWM master control chip. The output terminals are connected as follows: one end of the first secondary winding is connected to the secondary power supply terminal S_VCC via diode D28, and the other end of the first secondary winding is connected to the secondary signal ground SGND; one end of the second primary winding is connected to the first primary power supply terminal P_VCC via diode D27, and the other end of the second primary winding is connected to the primary power ground PGND; the input terminal of the isolation feedback circuit is connected to the secondary power supply terminal S_VCC or the first primary power supply terminal P_VCC; and the output terminal of the isolation feedback circuit is connected to the error amplifier compensation terminal of the PWM main control chip.

[0153] The PWM master control chip has a power supply terminal, a current detection terminal, a reference voltage terminal, a drive output terminal, a voltage feedback terminal, and an error amplifier compensation terminal.

[0154] In some embodiments, the voltage feedback terminal of the PWM master control chip is connected to the primary power ground PGND.

[0155] In some embodiments, the isolated power supply circuit further includes a resistor R143 and a capacitor C83. The resistor R143 and the capacitor C83 are connected in series, with one end connected to the error amplifier compensation terminal of the PWM main control chip and the other end connected to the primary power ground PGND.

[0156] In some embodiments, the isolated power supply circuit further includes a resistor R145 and a capacitor C84. One end of the resistor R145 is connected to the error amplifier compensation terminal of the PWM master control chip, and the other end of the resistor R145 is connected to one end of the capacitor C84 and the reference voltage terminal of the PWM master control chip, respectively. The other end of the capacitor C84 is connected to the primary power ground PGND.

[0157] In some embodiments, the isolated power supply circuit of the present invention further includes a transistor Q1. The first terminal of transistor Q1 is connected to the error amplifier compensation terminal of the PWM master control chip, the second terminal of transistor Q1 is connected to the voltage feedback terminal of the PWM master control chip, the control terminal of transistor Q1 is connected to one end of resistor R140 and one end of capacitor C81, the other end of resistor R140 is connected to the reference voltage AUX_REF, and the other end of capacitor C81 is connected to the primary power ground PGND. The voltage feedback terminal of the PWM master control chip is connected to the power ground PGND, and the control terminal of transistor Q1 is connected to the output terminal of the enable control circuit.

[0158] The isolated power supply circuit of the present invention further includes a third enable control circuit, which includes an input terminal for receiving a fault signal and an output terminal connected to the control electrode of transistor Q1.

[0159] The third enable control circuit includes transistors V9 and V3. The control electrode of transistor V9 is connected to the input terminal of the third enable control circuit via resistor R70. The control electrode of transistor V9 is connected to one end of resistor R71 and one end of capacitor C44. The other ends of resistor R71 and capacitor C44 are connected to power ground PGND. The second electrode of transistor V9 is connected to power ground PGND. The first electrode of transistor V9 is connected to one end of resistor R68 and the control electrode of transistor V3. The other end of resistor R68 is connected to positive voltage P_VCC. The second electrode of transistor V3 is connected to power ground PGND. The first electrode of transistor V3 is the output terminal of the third enable control circuit, which is used to connect to the control electrode of transistor Q1.

[0160] In some embodiments, the isolated power supply circuit of the present invention further includes a diode D31, the positive terminal of which is connected to the control terminal of transistor Q1, and the negative terminal of which is connected to the reference voltage AUX_REF.

[0161] In some embodiments, the isolation transformer further includes a third primary winding wound on the transformer core. One end of the third primary winding is connected to the second primary power supply terminal AUX_VCC via diode D29, and the other end of the third primary winding is connected to the primary power ground. The second primary power supply terminal AUX_VCC is connected to the power supply terminal VCC of the PWM master control chip, and the power supply terminal VCC of the PWM master control chip is connected to the positive terminal of the high voltage bus via a fourth resistor network.

[0162] In some embodiments, the isolated power supply circuit further includes a resistor R132 and a capacitor C77. The resistor R132 and the capacitor C77 are connected in series, with one end connected to the positive terminal of the diode D29 and one end of the third primary winding, and the other end connected to the negative terminal of the diode D29 and the second primary power supply terminal, respectively.

[0163] In some embodiments, the isolated power supply circuit further includes a capacitor C78, ​​one end of which is connected to the second primary power supply terminal, and the other end of which is connected to power ground.

[0164] In some embodiments, the current detection terminal of the PWM master control chip is connected to one end of resistor R150 and one end of capacitor C87, respectively. The other end of capacitor C87 is connected to the primary power ground. The other end of resistor R150 is connected to one end of resistor R155, one end of resistor R153 and one end of resistor R154, respectively. The other end of resistor R155 is connected to the control electrode of switching transistor V11. The other ends of resistor R153 and the other ends of resistor R154 are connected to the primary power ground.

[0165] In some embodiments, the isolation power supply circuit of the present invention further includes a second spike absorption network, the second spike absorption network including a fifth resistor network, a capacitor C79 and a diode D30, one end of the fifth resistor network and one end of the capacitor C79 are connected to one end of the first primary winding of the isolation transformer, the other end of the fifth resistor network and the capacitor C79 are connected to the negative terminal of the diode D30, and the positive terminal of the diode D30 is connected to the other end of the first primary winding of the isolation transformer.

[0166] In some embodiments, the isolation feedback circuit includes an optocoupler N18. The anode of the light-emitting diode of the optocoupler N18 is connected to one end of resistor R142 and one end of resistor R147, respectively. The other end of resistor R142 is connected to the secondary power supply terminal. The other end of resistor R147 is connected to the cathode of the light-emitting diode of the optocoupler N18, one end of resistor R148, and the cathode of the voltage regulator, respectively. The anode of the voltage regulator is connected to the primary power ground. The reference terminal of the voltage regulator is connected to one end of resistor R152, one end of resistor R146, and one end of capacitor C85, respectively. The other end of resistor R152 is connected to the primary power ground. The other end of resistor R146 is connected to the secondary power supply terminal. The other end of capacitor C85 is connected to the other end of resistor R148. The collector of the phototransistor of the optocoupler N18 is connected to the error amplifier compensation terminal of the PWM main control chip. The emitter of the phototransistor of the optocoupler N18 is connected to the primary power ground.

[0167] In some embodiments, the isolation power supply circuit further includes a resistor R126 and a capacitor C71. After the resistor R126 and the capacitor C71 are connected in series, one end is connected to the positive terminal of the diode D28 and one end of the first secondary winding, and the other end is connected to the negative terminal of the diode D28 and the secondary power supply terminal, respectively.

[0168] In some embodiments, the isolated power supply circuit of the present invention further includes at least one of capacitor C73, resistor R130, and resistor R131. One end of capacitor C73 is connected to the secondary power supply terminal, and the other end of capacitor C73 is connected to the secondary signal ground. One end of resistor R130 is connected to the secondary power supply terminal, and the other end of resistor R130 is connected to the secondary signal ground. One end of resistor R131 is connected to the secondary power supply terminal, and the other end of resistor R131 is connected to the secondary signal ground.

[0169] In some embodiments, the isolated power supply circuit further includes a capacitor C80, one end of which is connected to the primary power ground and the other end of which is connected to the secondary signal ground.

[0170] In some embodiments, the isolated power supply circuit further includes a resistor R125 and a capacitor C70. After the resistor R125 and the capacitor C70 are connected in series, one end is connected to the positive terminal of the diode D27 and one end of the second primary winding, and the other end is connected to the negative terminal of the diode D27 and the first primary power supply terminal, respectively.

[0171] In some embodiments, the isolated power supply circuit of the present invention further includes at least one of capacitors C74, C75, C76, and C72, one end of capacitors C74, C75, C76, and C72 is connected to the first primary power supply terminal, and the other end of capacitors C74, C75, C76, and C72 is connected to power ground.

[0172] In some embodiments, the isolated power supply circuit further includes a capacitor C80, one end of which is connected to power ground and the other end of which is connected to signal ground.

[0173] This invention discloses a high-frequency isolated switching power supply circuit (switching frequency 100kHz), whose core components include a switching transistor (V11, MOSFET), an isolation transformer, a control chip (U17), an optocoupler (N18), and rectifier / filter / buffer components.

[0174] The isolated switching power supply circuit of this invention achieves electrical isolation between the primary and secondary sides through a transformer, converting the input voltage (presumably high-voltage DC) into the target output voltage, while simultaneously outputting auxiliary power (AUXVCC). The isolated switching power supply circuit of this invention also uses an isolated feedback loop formed by an optocoupler (N18), in conjunction with a control chip (U17), to regulate the on / off state of the switching transistor, ensuring stable output voltage.

[0175] The isolated switching power supply circuit of this invention adopts a high-frequency switching topology (100kHz), which significantly improves energy conversion efficiency and reduces heat generation compared to linear power supplies. Through buffer circuits (such as the RC-D absorption circuit next to V11) and filter capacitors, electromagnetic interference (EMI) caused by high-frequency switching is suppressed, while the voltage spikes of the switching transistors are reduced, thus improving circuit reliability.

[0176] This invention's isolated switching power supply circuit achieves primary-secondary isolation through a transformer and optocoupler, avoiding direct electrical connection between high and low voltage sides. It is suitable for applications requiring safety isolation, such as medical and industrial control systems. For high frequencies of 100-500kHz, the buffer circuit of the switching transistor is optimized to reduce switching losses and improve power efficiency. The isolated feedback loop improves voltage stability accuracy under load changes, solving the delay / interference problems of traditional non-isolated feedback. This invention's isolated switching power supply circuit draws power from the transformer's auxiliary winding, and in conjunction with a rectification / filtering circuit, achieves self-powering for the control chip, solving the problems of slow auxiliary power supply startup and voltage fluctuations.

[0177] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in conjunction with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in conjunction with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as set forth in the appended claims.

Claims

1. A PFC-LLC resonant switching power supply, comprising a PFC circuit and an LLC circuit, wherein the input terminal of the PFC circuit is connected to an AC input interface, the output terminal of the PFC circuit is connected to the input terminal of the LLC circuit via a high-voltage bus, and the output terminal of the LLC circuit is connected to a DC output interface, characterized in that: It also includes a bus voltage sampling circuit, a fault detection circuit, a first enable control circuit, and a second enable control circuit. The input terminal of the first enable control circuit is connected to the output terminal of the fault detection circuit, and the output terminal of the first enable control circuit is connected to the voltage sampling terminal of the PFC control unit of the PFC circuit. The first input terminal of the second enable control circuit is connected to the output terminal of the fault detection circuit, and the output terminal of the second enable control circuit is connected to the voltage feedback input terminal of the LLC control unit of the LLC circuit. The input terminal of the bus voltage sampling circuit is connected to the input terminal of the LLC circuit, and the output terminal of the bus voltage sampling circuit is connected to the voltage feedback input terminal of the LLC control unit.

2. The PFC-LLC resonant switching power supply as described in claim 1, characterized in that: An AC input pre-stage protection circuit is provided between the input terminal of the PFC circuit and the AC input interface. The AC input pre-stage protection circuit includes a first EMI filter circuit and a common-mode noise cancellation unit. The common-mode noise cancellation unit includes a sampling network, an operational amplifier, and an injection capacitor. The input terminal of the first EMI filter circuit is connected to the AC input interface. One end of the sampling network is connected to the first output terminal of the first EMI filter circuit, and the other end of the sampling network is connected to the second output terminal of the first EMI filter circuit. The sampling output point of the sampling network is connected to one input terminal of the operational amplifier. The output terminal of the operational amplifier is connected to one end of the injection capacitor, and the other end of the injection capacitor is connected to protective ground.

3. The PFC-LLC resonant switching power supply as described in claim 2, characterized in that: The first EMI filter circuit includes a common-mode inductor L5. The first input terminal of the common-mode inductor L5 is connected to the live wire input terminal of the AC input interface, the second input terminal of the common-mode inductor L5 is connected to the neutral wire input terminal of the AC input interface, the first output terminal of the common-mode inductor L5 is connected to the first output terminal of the first EMI filter circuit, and the second output terminal of the common-mode inductor L5 is connected to the second output terminal of the first EMI filter circuit. The first EMI filter circuit also includes a first Y capacitor and a second Y capacitor. One end of the first Y capacitor is connected to the first output terminal of the first EMI filter circuit, and the other end of the first Y capacitor is connected to protective ground. One end of the second Y capacitor is connected to the second output terminal of the first EMI filter circuit, and the other end of the second Y capacitor is connected to protective ground.

4. The PFC-LLC resonant switching power supply as described in claim 2 or 3, characterized in that: The AC input pre-stage protection circuit also includes a bypass switch and a PTC resistor connected in series on the live wire of the AC input. The bypass switch and the PTC resistor are connected in parallel. The bypass switch is connected to a switch drive circuit. The input terminal of the switch drive circuit is connected to the output terminal of the undervoltage detection circuit.

5. The PFC-LLC resonant switching power supply as described in claim 1, characterized in that: The PFC circuit includes a PFC power main circuit and a PFC control unit. The PFC power main circuit includes a rectifier circuit and a main switch V15. The positive output terminal of the rectifier circuit is connected to the positive terminal of the high-voltage bus via a boost inductor L4 and a freewheeling diode D22. The negative output terminal of the rectifier circuit is connected to the negative terminal of the high-voltage bus. The first terminal of the main switch V15 is connected between the positive terminal of the boost inductor L4 and the positive terminal of the freewheeling diode D22. The second terminal of the main switch V15 is connected to the negative terminal of the high-voltage bus and the power ground. The control terminal of the main switch V15 is connected to the output terminal of the PFC control unit via a first switch drive circuit. The PFC power main circuit also includes a sampling resistor RS1. One end of the sampling resistor RS1 is connected to the negative output terminal of the rectifier circuit and the input terminal of the first current sampling circuit. The other end of the sampling resistor RS1 is connected to the negative terminal of the high voltage bus. The output terminal of the first current sampling circuit is connected to the current sampling input terminal of the LLC control unit.

6. The PFC-LLC resonant switching power supply as described in claim 1, characterized in that: The fault detection circuit includes an undervoltage detection circuit and an overvoltage detection circuit. The output terminal of the undervoltage detection circuit is connected to the first signal output terminal via diode D33, and the output terminal of the overvoltage detection circuit is connected to the first signal output terminal via diode D37. The first signal output terminal is connected to a positive voltage via resistor R127. The first signal output terminal is connected to the second signal output terminal VIN_CTRL via an output filter circuit. The second signal output terminal VIN_CTRL is the output terminal of the fault detection circuit. The undervoltage detection circuit includes an operational amplifier N13A. The inverting input terminal of the operational amplifier N13A is connected to a reference voltage via a resistor R129. The non-inverting input terminal of the operational amplifier N13A is connected to the voltage sampling terminal of the undervoltage detection circuit via a resistor R130. The output terminal of the operational amplifier N13A is connected to the non-inverting input terminal of the operational amplifier N13A via a first feedback branch. A feedback resistor R140 and a diode D34 are connected in series in the first feedback branch. The output terminal of the operational amplifier N13A is the output terminal of the undervoltage comparator circuit. The overvoltage detection circuit includes an operational amplifier N13B. The inverting input terminal of the operational amplifier N13B is connected to the voltage sampling terminal of the overvoltage detection circuit via a resistor R146. The non-inverting input terminal of the operational amplifier N13B is connected to the reference voltage via a resistor R152. The output terminal of the operational amplifier N13B is connected to the non-inverting input terminal of the operational amplifier N13B via a second feedback branch. A feedback resistor R154 and a diode D38 are connected in series in the second feedback branch. The output terminal of the operational amplifier N13B is the output terminal of the overvoltage comparator circuit. The first enable control circuit includes a main switch V19 and a main switch V18. The control terminal of the main switch V19 is connected to the output terminal of the fault detection circuit via a resistor R147. The first terminal of the main switch V19 is connected to the control terminal of the main switch V18 and one end of the resistor R143. The other end of the resistor R143 is connected to a positive voltage. The second terminal of the main switch V19 is connected to power ground. The first terminal of the main switch V18 is connected to the voltage sampling terminal of the PFC control unit. The second terminal of the main switch V18 is connected to power ground. The voltage sampling terminal of the PFC control unit is connected to the output terminal of the first bus voltage sampling circuit. The input terminal of the first bus voltage sampling circuit is connected to the positive terminal of the high-voltage bus.

7. The PFC-LLC resonant switching power supply as described in claim 1, characterized in that: The LLC circuit includes an LLC control unit, a transformer T1, an inductor L1, and main switching transistors V1 and V10. The first terminal of the main switching transistor V1 is connected to the positive terminal of the high-voltage bus. The second terminal of the main switching transistor V1 is connected to the first terminal of the main switching transistor V10, one end of the inductor L1, and the midpoint feedback terminal of the half-bridge of the LLC control unit. The second terminal of the main switching transistor V10 is connected to the negative terminal of the high-voltage bus. The other end of the inductor L1 is connected to one end of the primary winding of the transformer T1. The other end of the primary winding of the transformer T1 is connected to the positive terminal of the high-voltage bus via capacitor C35. The other end of the primary winding of the transformer T1 is connected to the negative terminal of the high-voltage bus via capacitor C44. The other end of the primary winding of the transformer T1 is connected to the anode of diode D2. The cathode of diode D2 is connected to the positive terminal of the high-voltage bus. The other end of the primary winding of the transformer T1 is connected to the cathode of diode D3. The anode of diode D3 is connected to the negative terminal of the high-voltage bus. The other end of the primary winding of the transformer T1 is connected to the input terminal of the second current sampling circuit, the output terminal of the second current sampling circuit is connected to the current sampling input terminal of the LLC control unit, the secondary winding of the transformer T1 is connected to the DC output interface through the rectifier circuit, the control electrode of the main switch V1 is connected to the upper tube drive output terminal of the LLC control unit through the second switch drive circuit, and the control electrode of the main switch V10 is connected to the lower tube drive output terminal of the LLC control unit through the third switch drive circuit.

8. The PFC-LLC resonant switching power supply as described in claim 7, characterized in that: The LLC circuit also includes a first voltage monitoring circuit. The input terminal of the first voltage monitoring circuit is connected to the DC output interface, the output terminal of the first voltage monitoring circuit is connected to the input terminal of the first isolation output circuit, the output terminal of the first isolation output circuit is connected to the standby / light load control terminal of the LLC control unit via resistor R61, and the output terminal of the first isolation output circuit is connected to the minimum frequency setting terminal of the LLC control unit via resistor R57. The LLC circuit also includes a second voltage monitoring circuit and an external enable input network. The output terminal of the second voltage monitoring circuit is connected to the input terminal of the second isolation output circuit via diode D13. The output terminal of the external enable input network is connected to the input terminal of the second isolation output circuit via diode D14. The output terminal of the second isolation output circuit is connected to the second input terminal of the second enable control circuit. The LLC circuit also includes a second bus voltage sampling circuit. The input terminal of the second bus voltage sampling circuit is connected to the positive terminal of the high-voltage bus, and the output terminal of the second bus voltage sampling circuit is connected to the voltage feedback input terminal of the LLC control unit.

9. The PFC-LLC resonant switching power supply as described in claim 8, characterized in that: The first voltage monitoring circuit includes an operational amplifier N3A. The non-inverting input terminal of the operational amplifier N3A is connected to the voltage divider point of the first resistor network via a resistor R41. One end of the first resistor network is connected to the positive terminal of the DC output interface, and the other end of the first resistor network is connected to the negative terminal of the DC output interface. The inverting input terminal of the operational amplifier N3A is connected to the reference voltage via a resistor R36. The output terminal of the operational amplifier N3A is connected to the inverting input terminal of the operational amplifier N3A via a third feedback branch. The output terminal of the operational amplifier N3A is connected to the output terminal of the first voltage monitoring circuit and the input terminal of the first isolation output circuit via a resistor R40. A feedback resistor R35 and a capacitor C53 are connected in series in the third feedback branch. And / or, The second voltage monitoring circuit includes operational amplifier N3B. The inverting input terminal of operational amplifier N3B is connected to a reference voltage via resistor R67. The non-inverting input terminal of operational amplifier N3B is connected to the voltage divider point of the second resistor network. One end of the second resistor network is connected to the positive terminal of the DC output interface, and the other end of the second resistor network is connected to the negative terminal of the DC output interface. The output terminal of operational amplifier N3B is connected to the non-inverting input terminal of operational amplifier N3B via a fourth feedback branch. The output terminal of operational amplifier N3B is connected to one end of resistor R66 and one end of resistor R59, respectively. The other end of resistor R59 is connected to the positive voltage S_VCC. The other end of resistor R66 is the output terminal of the second voltage monitoring circuit. A feedback resistor R53 and a diode D11 are connected in series in the fourth feedback branch. And / or, The external enable input network includes resistors R72 and R71. One end of resistor R72 is connected to one end of resistor R71 and the input terminal EN of the external enable input network. The other end of resistor R71 is connected to the positive voltage S_VCC. The other end of resistor R72 is the output terminal of the external enable input network. And / or, The second bus voltage sampling circuit includes a second high-voltage divider network. One end of the second high-voltage divider network is connected to the positive terminal of the high-voltage bus, and the other end of the second high-voltage divider network is connected to the power ground. The voltage division point of the high-voltage divider network is connected to one end of resistor R58. The other end of resistor R58 is connected to one end of capacitor C64 and the voltage feedback input terminal of the LLC control unit, respectively. The other end of capacitor C64 is connected to the power ground.

10. The PFC-LLC resonant switching power supply as described in claim 1 or 8, characterized in that: The second enable control circuit includes a main switch V13 and a main switch V12. The control terminal of the main switch V13 is the first input terminal of the second enable control circuit. The first input terminal of the second enable control circuit is connected to the second input terminal of the second enable control circuit via a resistor R76. The control terminal of the main switch V13 is connected to one end of a resistor R77 and one end of a capacitor C72. The other ends of the resistor R77 and the other ends of the capacitor C72 are connected to power ground PGND. The second terminal of the main switch V13 is connected to power ground PGND. The first terminal of the main switch V13 is connected to one end of a resistor R75 and the control terminal of the main switch V12. The other end of the resistor R75 is connected to the positive voltage P_VCC. The second terminal of the main switch V12 is connected to power ground PGND. The first terminal of the main switch V12 is connected to one end of a resistor R74. The other end of the resistor R74 is the output terminal of the second enable control circuit.

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