Switching power supply circuit for HPLC

Abstract

The utility model provides a switching power supply circuit for HPLC (High Performance Liquid Chromatography). The switching power supply circuit comprises an input rectification circuit, a switching power supply conversion circuit and a low-pass filter circuit, the input rectification circuit comprises a first LC filter and a rectifier, the input end of the first LC filter is connected with the mains supply, the output end of the first LC filter is connected with the input end of the rectifier, the output end of the rectifier is connected with the input end of the switching power supply conversion circuit, and the switching power supply conversion circuit carries out voltage reduction processing on an output signal of the rectifier; the low-pass filter circuit comprises a second LC filter, and the input end of the second LC filter is connected with the output end of the switching power supply conversion circuit. According to the switching power supply conversion circuit, switching frequency multiplication noise coupled back to a power line along a rectifier path is filtered through the first LC filter, interference on HPLC signals transmitted on the power line is reduced, switching frequency multiplication noise in power supply signals output by the switching power supply conversion circuit is filtered through the second LC filter, and clean and stable power supply signals are provided.

Description

Technical Field

[0001] The utility model relates to the technical field of switching power supply circuits, in particular to a switching power supply circuit for HPLC. Background Art

[0002] Low-voltage power line high-speed carrier communication, or HPLC, is a power line carrier communication technology that uses power lines as the carrier medium. The transmitter couples the signal onto the power line, and the receiver re-couples the received signal to complete a communication. The communication frequency ranges from 700 kHz to 12 MHz. The HPLC circuits (including HPLC communication chip circuits and RF power amplifier circuits) at both the transmitter and receiver are sensitive to noise and require a low-noise power supply. In the early days, linear power supplies were generally used as the power supply for HPLC circuits.

[0003] Although linear power supplies offer low noise, they are also low-power, inefficient, bulky, and significantly affected by supply voltage. These power supplies are only suitable for low-power communication modules and cannot meet the increasing power and shrinking size requirements of HPLC circuits. Switching power supplies offer high power, compact size, high efficiency, and a wide supply voltage range. However, they generate switching frequency multiplication noise (switching frequencies range from 100 to several hundred kHz, such as 500 kHz and 600 kHz). This switching frequency multiplication noise falls squarely within the HPLC communication frequency range and can easily interfere with HPLC communication signals when supplying power to HPLC circuits. Furthermore, this switching frequency multiplication noise can also couple back through the switching power supply's mains power supply path to the power lines, interfering with HPLC signals transmitted along the power lines.

[0004] Existing switching power supply circuits often include a filter at the power supply signal output to filter out switching frequency noise. For example, Chinese patent application number CN109039089A discloses an isolated switching power supply with an ultra-wide voltage input. Referring to Figure 3 of the accompanying drawings in its specification, an LC filter consisting of inductor L2 and capacitor C12 is provided at the output of transformer T2 in the power supply circuit. This LC filter can filter out switching frequency multiplication noise at the output of the switching power supply. However, this patented power supply circuit is unable to process the switching frequency multiplication noise coupled back from the switching power supply's mains power supply path, causing the switching frequency multiplication noise to couple back into the power lines. This makes it unsuitable for HPLC applications and can interfere with HPLC communications on the power lines.

[0005] Therefore, there is an urgent need to provide a switching power supply circuit suitable for HPLC communication that can effectively reduce switching power supply noise. Utility Model Content

[0006] The utility model aims to solve the technical problem that the existing switching power supply circuit cannot effectively suppress switching frequency noise and interferes with HPLC communication, and provides a switching power supply circuit for HPLC.

[0007] In order to achieve the above-mentioned purpose of the utility model, the utility model provides a switching power supply circuit for HPLC, including an input rectifier circuit, a switching power supply conversion circuit and a low-pass filter circuit; the input rectifier circuit includes a first LC filter and a rectifier, the input end of the first LC filter is connected to the mains, the output end of the first LC filter is connected to the input end of the rectifier, the output end of the rectifier is connected to the input end of the switching power supply conversion circuit, and the switching power supply conversion circuit performs a voltage reduction process on the rectifier output signal; the low-pass filter circuit includes a second LC filter, the input end of the second LC filter is connected to the output end of the switching power supply conversion circuit.

[0008] The above technical solution: a first LC filter is set before the rectifier of the input rectifier circuit. The first LC filter has excellent high-frequency suppression and has bidirectional filtering characteristics. Compared with the single capacitor grounding filtering, its filtering frequency range is wider. The first LC filter can effectively filter out the switching frequency multiplication noise from the switching power supply conversion circuit coupled back to the power line along the rectifier path, reduce interference with the strong electric circuit, and thus reduce interference with the HPLC signal transmitted on the power line; at the same time, a second LC filter is set in the low-pass filter circuit, which has the characteristics of wide filtering frequency range and good high-frequency suppression effect, and can effectively filter out the switching frequency multiplication noise in the power signal output by the switching power supply conversion circuit, provide a clean and stable power signal for the subsequent HPLC circuit, and improve the HPLC communication quality.

[0009] In a preferred embodiment of the present invention, the low-pass filter circuit further includes at least one intermediate element, and the at least one intermediate element is connected in series on the connection path between the output end of the switching power conversion circuit and the input end of the second LC filter.

[0010] The above technical solution: The switching frequency multiplication noise of the switching power supply is high-frequency noise. High-frequency noise can not only be transmitted through the line, but also enter the line through spatial coupling. High-frequency noise can easily enter longer wires, especially longer power signal wires, through spatial coupling. Therefore, when the HPLC switching power supply circuit is actually laid out and wired, in order to reduce the high-frequency noise spatially coupled into the connection path between the output end of the switching power supply conversion circuit and the input end of the second LC filter, an intermediate element is set in the connection path to reduce the wire length, and a star connection method is conveniently arranged during wiring to further reduce the noise spatially coupled into.

[0011] In a preferred embodiment of the present invention, the intermediate element is a sixth diode, the anode of the sixth diode is connected to the output end of the switching power conversion circuit, and the cathode of the sixth diode is connected to the input end of the second LC filter.

[0012] The above technical solution: the intermediate element is set as a diode, which has a small voltage drop, small power loss, and a unidirectional conduction characteristic, thereby preventing current backflow and protecting the switching power supply circuit.

[0013] In a preferred embodiment of the present invention, the second LC filter includes a ninth capacitor, a fifth inductor, and an eleventh capacitor, wherein the first end of the fifth inductor is respectively connected to one end of the intermediate element and the first end of the ninth capacitor, the second end of the fifth inductor is connected to the first end of the eleventh capacitor, and the second end of the ninth capacitor and the second end of the eleventh capacitor are both connected to a DC ground.

[0014] The above technical solution: The second LC filter composed of the ninth capacitor, the fifth inductor and the eleventh capacitor is a third-order low-pass filter circuit. There is no voltage drop when in use, and the loss is small when transmitting the power signal. The inductance value and the capacitance value can be flexibly adjusted according to the switching frequency to adjust the cutoff frequency, effectively filtering out the switching frequency multiplication noise.

[0015] In a preferred embodiment of the present utility model, the low-pass filter circuit also includes a noise elimination circuit arranged at the output end of the switching power conversion circuit, the noise elimination circuit includes a fifteenth resistor, a tenth capacitor and a third diode, the first end of the fifteenth resistor is respectively connected to the anode of the third diode and the output end of the switching power conversion circuit, the second end of the fifteenth resistor is connected to the first end of the tenth capacitor, and the second end of the tenth capacitor is respectively connected to the cathode of the third diode and one end of the intermediate element.

[0016] The above technical solution can effectively eliminate the noise signal generated by the switching power supply conversion circuit.

[0017] In a preferred embodiment of the present invention, the low-pass filter circuit further includes an output energy storage capacitor, a first end of the output energy storage capacitor is connected to the second end of the tenth capacitor, and a second end of the output energy storage capacitor is connected to a DC ground.

[0018] The above technical solution can effectively reduce the ripple of the output power signal.

[0019] In a preferred embodiment of the present invention, the first LC filter includes a third inductor and a twelfth capacitor, the first end of the third inductor is connected to the mains live wire, the second end of the third inductor is respectively connected to the first end of the twelfth capacitor and the input end of the rectifier, and the second end of the twelfth capacitor is connected to the mains neutral wire.

[0020] The above technical solution: The first LC filter formed by the switching power supply conversion circuit can achieve bidirectional operation, which can not only filter out high-frequency noise in the mains to prevent it from entering the switching power supply conversion circuit, but also prevent the switching frequency multiplication noise generated by the switching power supply circuit from coupling back to the mains power grid.

[0021] In a preferred embodiment of the present invention, the input rectifier circuit further includes a common-mode inductor connected in series between the first LC filter and the rectifier.

[0022] The above technical solution is used to absorb common-mode signals in the power grid.

[0023] In a preferred embodiment of the present invention, the input rectifier circuit further includes a varistor located before the first filter, a first end of the varistor is connected to the mains live wire, and a second end of the varistor is connected to the mains neutral wire.

[0024] The above technical solution: absorbing high-voltage pulses or surges in the power grid through varistors to protect subsequent circuits.

[0025] In a preferred embodiment of the present invention, the input rectifier circuit also includes an input energy storage capacitor, the first end of the input energy storage capacitor is respectively connected to the high voltage output end of the rectifier and the input end of the switching power conversion circuit, and the second end of the input energy storage capacitor is connected to the DC ground.

[0026] The above technical solution converts the positive steamed bun wave output by the rectifier into high-voltage direct current, which has a low-pass filtering effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a structural block diagram of a switching power supply circuit for HPLC provided by the utility model;

[0028] Figure 2 This is a connection diagram of the HPLC switching power supply circuit in a preferred embodiment of the present invention.

[0029] Reference numerals: 1 input rectification circuit; 11 first LC filter; 2 switching power supply conversion circuit; 3 low-pass filtering circuit; 31 second LC filter; 32 noise elimination circuit. DETAILED DESCRIPTION

[0030] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0031] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0032] In the description of the present utility model, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two components. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0033] The utility model discloses a switching power supply circuit for HPLC. In a preferred embodiment, referring to Figure 1 As shown, the switching power supply circuit includes an input rectifier circuit 1, a switching power conversion circuit 2 and a low-pass filter circuit 3; the input rectifier circuit 1 includes a first LC filter 11 and a rectifier, the input end of the first LC filter 11 is connected to the mains, the output end of the first LC filter 11 is connected to the input end of the rectifier, the output end of the rectifier is connected to the input end of the switching power conversion circuit 2, and the switching power conversion circuit 2 performs a voltage reduction process on the rectifier output signal; the low-pass filter circuit 3 includes a second LC filter 31, the input end of the second LC filter 31 is connected to the output end of the switching power conversion circuit 2.

[0034] In this embodiment, the first LC filter 11 is preferably but not limited to the existing second-order or third-order LC low-pass filter circuit 3. Figure 2 As shown, the first LC filter 11 includes a third inductor L3 and a twelfth capacitor C12, forming a second-order low-pass filter. The first end of the third inductor L3 is connected to the mains live wire, the second end of the third inductor L3 is connected to the first end of the twelfth capacitor C12 and the input end of the rectifier, respectively, and the second end of the twelfth capacitor C12 is connected to the mains neutral wire. The cutoff frequency of the first LC filter 11 is lower than the switching frequency of the switching power supply chip in the switching power supply conversion circuit 2, such as lower than 500KHz. The first LC filter 11 simultaneously absorbs high-frequency noise input from the power grid and switching frequency multiplier noise coupled back from the subsequent switching power supply conversion circuit 2.

[0035] In this embodiment, the rectifier U201 is preferably but not limited to an existing full-bridge or half-bridge rectifier chip, and the model is not limited to MB10S or CX7538B, which will not be described in detail here.

[0036] In this embodiment, the second LC filter 31 is preferably, but not limited to, an existing second-order or third-order LC low-pass filter circuit. In order to better filter high-frequency noise (switching frequency multiplication noise) and provide a clean and stable low-voltage power supply for the subsequent HPLC circuit, it is further preferred to refer to Figure 2 As shown, the second LC filter 31 is a third-order low-pass LC filter circuit, specifically including a ninth capacitor C9, a fifth inductor L5, and an eleventh capacitor C11. The first end of the fifth inductor L5 is connected to one end of the intermediate element and the first end of the ninth capacitor C9, respectively. The second end of the fifth inductor L5 is connected to the first end of the eleventh capacitor C11. The second end of the ninth capacitor C9 and the second end of the eleventh capacitor C11 are both connected to the DC ground GND. In one example, the cutoff frequency of the second LC filter 31 is designed to be 16.5 kHz, the inductance of the fifth inductor L5 is 1 mH, and the capacitance of the ninth capacitor C9 and the eleventh capacitor C11 are both 220 nF. Since the switching frequency of the switching power supply is 500 kHz, this can effectively suppress high-frequency noise, resulting in almost no interference in the output voltage, thus resolving the problem of high-frequency interference from the switching power supply affecting the communication of the subsequent HPLC module.

[0037] In this embodiment, the switching power conversion circuit 2 can use an existing AC-DC switching power supply chip and its peripheral circuits. The AC-DC switching power supply chip is preferably, but not limited to, CN1611, NCP1252ADR2G, BL8028, MAX77324, or MP2105. The switching power conversion circuit 2 can be designed according to the chip manual of the selected AC-DC switching power supply chip, which will not be described in detail here. In this case, the output end of the rectifier is connected to the input end of the switching power conversion circuit 2, mainly referring to the output end of the rectifier being connected to one end of the primary coil of the coupling transformer in the switching power conversion circuit 2, and also providing a power supply signal to the AC-DC switching power supply chip. The low-pass filter circuit 3 is used to rectify the voltage of the secondary coil and output it to eliminate high-frequency noise of the switching power supply. In addition, the switching power conversion circuit 2 can also adopt the existing DC-DC switching power supply chip and its peripheral circuits. The DC-DC switching power supply chip is preferably but not limited to AH9200 or AH7691X. The switching power conversion circuit 2 can be designed according to the chip manual of the selected DC-DC switching power supply chip, which will not be repeated here. At this time, the output end of the rectifier is connected to the input end of the switching power conversion circuit 2, which mainly refers to the connection between the output end of the rectifier and the voltage input end of the DC-DC switching power supply chip. Similarly, the low-pass filter circuit 3 is used to eliminate the high-frequency noise of the switching power supply.

[0038] In one example, the switching power conversion circuit 2 includes an AC-DC switching power chip CN1611 and its peripheral circuits. Figure 2 As shown, U1 is the AC-DC switching power supply chip CN1611. The high-voltage DC signal after rectification by the input rectification circuit 1 passes through the seventh resistor R7, the eighth resistor R8 and the tenth resistor R10 connected in series and reaches the cathode of the voltage-stabilizing diode D4. Then, it is powered by the chip-end energy storage capacitor C1 to power the switching power supply chip U1. The switching power supply chip U1 starts working. Synchronously, the high-voltage DC signal after rectification by the input rectification circuit 1 is also connected to one end of the primary coil of the coupling transformer T1. The other end of the primary coil is connected to the high-voltage port (HV) of the switching power supply chip U1. At this time, the switching power supply chip U1 is already working and controls the on and off of the high-voltage port (HV) in the form of chopping. When the high-voltage port (HV) voltage is turned on, the primary coil of the coupling transformer is full of electric potential energy. When the high-voltage port (HV) voltage is turned off, the coupling transformer T 1, the current in the primary coil releases energy through the second diode D2, the sixth resistor R6, and the fifth capacitor C5, and at the same time achieves the purpose of resetting the magnetic field, preparing for the next energy storage and energy transfer of the coupling transformer T1; by controlling the high voltage port (HV) to be continuously on and off, the electric potential energy is transferred to the secondary coil, and the secondary coil outputs a stepped-down DC power supply signal to power the subsequent HPLC circuit; at the same time, the primary coil of the coupling transformer T1 transfers the electric potential energy to the secondary coil, and the electric signal output by the secondary coil passes through the ninth resistor R9 and the first fast-recovery diode D1 in turn to power the switching power supply chip U1; the secondary coil is also connected to the feedback circuit, which is composed of the fourth resistor R4, the third resistor R3 and the third capacitor C2 according to Figure 2 The connection relationship shown in the figure is composed of the feedback circuit, which transmits the feedback voltage to the feedback terminal VS of the switching power supply chip U1. The switching power supply chip U1 obtains a stable DC output voltage by adjusting the voltage shutdown duty cycle.

[0039] In a preferred embodiment, Figure 2 As shown, the low-pass filter circuit 3 further includes at least one intermediate element, which is connected in series to the connection path between the input end of the second LC filter 31 and the output end of the switching power conversion circuit 2 .

[0040] In this embodiment, the intermediate element is a low voltage drop element, which can be used to segment a long wire. In order to reduce the power loss of the intermediate element, the intermediate element is preferably, but not limited to, a 0 ohm resistor or a diode. When there are more than one intermediate element, the intermediate elements are spaced apart by a preset distance. Preferably, an intermediate element is provided on the connection path between the input end of the second LC filter 31 and the output end of the switching power conversion circuit 2. The intermediate element has two connection ends, referring to Figure 2As shown, the first end of the output energy storage capacitor C7 connected to the first end of the intermediate element, the second end of the tenth capacitor C10, and the cathode of the third diode D3 are wired in a star wiring manner, and the first end of the fifth inductor L5 connected to the second end of the intermediate element and the first end of the ninth capacitor C9 are also wired in a star wiring manner, which can further reduce high-frequency noise caused by spatial coupling.

[0041] In this embodiment, it is further preferred that Figure 2 As shown, the intermediate element is a sixth diode D6 , the anode of the sixth diode D6 is connected to the output end of the switching power conversion circuit 2 , and the cathode of the sixth diode D6 is connected to the input end of the second LC filter 31 .

[0042] In a preferred embodiment, Figure 2 As shown, the low-pass filter circuit 3 also includes a noise elimination circuit 32 provided at the output end of the switching power conversion circuit 2, for eliminating noise signals on the coupling transformer T1. The noise elimination circuit 32 includes a fifteenth resistor R15, a tenth capacitor C10, and a third diode D3. The first end of the fifteenth resistor R15 is respectively connected to the anode of the third diode D3 and the output end of the switching power conversion circuit 2, the second end of the fifteenth resistor R15 is connected to the first end of the tenth capacitor C10, and the second end of the tenth capacitor C10 is respectively connected to the cathode of the third diode D3 and one end of the intermediate element.

[0043] In this embodiment, it is further preferred that Figure 2 As shown, the low-pass filter circuit 3 also includes an output energy storage capacitor C7. The first end of the output energy storage capacitor C7 is connected to the second end of the tenth capacitor C10, and the second end of the output energy storage capacitor is connected to the DC ground GND. The output energy storage capacitor C7 can use a large-capacity electrolytic capacitor, such as a capacitance of 1000uF, to effectively reduce power supply ripple.

[0044] In a preferred embodiment, Figure 2 As shown, the input rectifier circuit 1 further includes a common mode inductor L1 connected in series between the first LC filter 11 and the rectifier. Specifically, when the first LC filter 11 is composed of Figure 2 When the third inductor L3 and the twelfth capacitor C12 are formed as shown, the third inductor L3 is connected to the first end of the first coil of the common-mode inductor L1, the mains is connected to the first end of the second coil of the common-mode inductor L1, the second end of the first coil of the common-mode inductor L1 is connected to the high-voltage input terminal of the rectifier U201, and the second end of the second coil of the common-mode inductor L1 is connected to the low-voltage input terminal of the rectifier U201. Power flows through the common-mode inductor L1, absorbing the common-mode signal from the power grid. The processed AC signal is free of noise and is very clean.

[0045] In a preferred embodiment, Figure 2 As shown, the input rectifier circuit 1 further includes a varistor VR1 located before the first filter. The first end of the varistor VR1 is connected to the mains live line, and the second end of the varistor VR1 is connected to the mains neutral line. High-voltage pulses or surges in the power grid are absorbed by the varistor VR1.

[0046] In a preferred embodiment, Figure 2 As shown, the input rectifier circuit 1 also includes an input energy storage capacitor C2. The first end of the input energy storage capacitor C2 is connected to the high-voltage output end of the rectifier and the input end of the switching power conversion circuit 2, respectively. The second end of the input energy storage capacitor C2 is connected to the DC ground GND. The AC current passes through the rectifier U201, which rectifies the AC into a positive steamed bun wave. The positive steamed bun wave flows into the input energy storage capacitor C2 for energy storage, thereby obtaining the required high-voltage DC power. The input energy storage capacitor C2 is preferably an electrolytic capacitor with a large capacitance value, such as 1000uF.

[0047] The utility model provides a switching power supply circuit for HPLC, in which a first LC filter 11 is arranged before the rectifier to better suppress the switching frequency multiplication noise (including switching frequency multiplication noise of 1 times and above) of the switching power supply conversion circuit 2, and prevent the high-frequency interference noise of the switching power supply from being coupled back into the power line; a second LC filter 31 is provided on the power supply path of the switching power supply conversion circuit 2, adopting a third-order low-pass filter circuit structure, adjusting the inductance and capacitance values ​​according to the switching frequency, and having a cut-off frequency of 16 kHz, which can perfectly suppress the interference frequency of the switching power supply and prevent it from entering the subsequent HPLC circuit; in addition, an intermediate element is provided on the power supply path of the switching power supply conversion circuit 2 to reduce the switching frequency multiplication noise on the PCB printed circuit board from entering the power supply path through spatial coupling, thereby interfering with HPLC communication. The above three aspects are combined with each other to effectively filter out the influence of the switching frequency multiplication noise on HPLC communication, and can provide a very clean and stable power supply for the HPLC high-speed power line carrier.

[0048] Throughout this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," "one implementation," "a preferred implementation," or "some examples" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0049] Although the embodiments of the present invention have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and purpose of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A switching power supply circuit for HPLC, characterized in that: Including input rectification circuit, switching power supply conversion circuit and low-pass filter circuit; The input rectifier circuit includes a first LC filter and a rectifier, wherein the input end of the first LC filter is connected to the mains, the output end of the first LC filter is connected to the input end of the rectifier, and the output end of the rectifier is connected to the input end of the switching power conversion circuit, and the switching power conversion circuit performs a voltage reduction process on the rectifier output signal; The low-pass filter circuit includes a second LC filter, and the input end of the second LC filter is connected to the output end of the switching power conversion circuit.

2. A switching power supply circuit for HPLC according to claim 1, characterized in that: The low-pass filter circuit further includes at least one intermediate element, which is connected in series to a connection path between the output end of the switching power conversion circuit and the input end of the second LC filter.

3. A switching power supply circuit for HPLC as claimed in claim 2, characterized in that: The intermediate element is a sixth diode, an anode of the sixth diode is connected to the output end of the switching power conversion circuit, and a cathode of the sixth diode is connected to the input end of the second LC filter.

4. A switching power supply circuit for HPLC according to claim 2 or 3, characterized in that: The second LC filter includes a ninth capacitor, a fifth inductor, and an eleventh capacitor. The first end of the fifth inductor is respectively connected to one end of the intermediate element and the first end of the ninth capacitor. The second end of the fifth inductor is connected to the first end of the eleventh capacitor. The second end of the ninth capacitor and the second end of the eleventh capacitor are both connected to a DC ground.

5. A switching power supply circuit for HPLC as claimed in claim 4, characterized in that: The low-pass filter circuit further includes a noise elimination circuit provided at the output end of the switching power supply conversion circuit; The noise elimination circuit includes a fifteenth resistor, a tenth capacitor and a third diode, the first end of the fifteenth resistor is respectively connected to the anode of the third diode and the output end of the switching power conversion circuit, the second end of the fifteenth resistor is connected to the first end of the tenth capacitor, and the second end of the tenth capacitor is respectively connected to the cathode of the third diode and one end of the intermediate element.

6. A switching power supply circuit for HPLC as claimed in claim 5, characterized in that: The low-pass filter circuit further includes an output energy storage capacitor, a first end of the output energy storage capacitor is connected to the second end of the tenth capacitor, and a second end of the output energy storage capacitor is connected to a DC ground.

7. A switching power supply circuit for HPLC according to claim 1, 2, 3, 5 or 6, characterized in that: The first LC filter includes a third inductor and a twelfth capacitor, the first end of the third inductor is connected to the mains live wire, the second end of the third inductor is respectively connected to the first end of the twelfth capacitor and the input end of the rectifier, and the second end of the twelfth capacitor is connected to the mains neutral wire.

8. A switching power supply circuit for HPLC according to claim 7, characterized in that: The input rectifier circuit further includes a common mode inductor connected in series between the first LC filter and the rectifier.

9. A switching power supply circuit for HPLC according to claim 1 or 2 or 3 or 5 or 6 or 8, characterized in that: The input rectifier circuit further includes a varistor located before the first filter, wherein a first end of the varistor is connected to the live wire of the mains, and a second end of the varistor is connected to the neutral wire of the mains.

10. A switching power supply circuit for HPLC according to claim 9, characterized in that: The input rectifier circuit also includes an input energy storage capacitor, a first end of which is connected to the high voltage output end of the rectifier and the input end of the switching power conversion circuit respectively, and a second end of the input energy storage capacitor is connected to the DC ground.

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