Three-phase digital power supply auxiliary power supply circuit based on resistance-capacitance step-down circuit

Abstract

The invention relates to the technical field of power electronics, in particular to a three-phase digital power supply auxiliary power supply circuit based on a resistance-capacitance step-down circuit, which comprises a three-phase power supply, the resistance-capacitance step-down circuit, a Buck circuit, an LDO circuit, a control circuit, a drive circuit, a flyback circuit, a three-phase PFC module and a three-phase PFC direct current bus, wherein the resistance-capacitance step-down circuit is respectively connected with the Buck circuit and the driving circuit; the three-phase PFC DC bus is connected with the flyback circuit; the flyback circuit is connected with the Buck circuit and the drive circuit. According to the auxiliary power supply structure based on the resistance-capacitance step-down circuit, efficient energy taking can be achieved through an existing direct-current bus or a specific potential point in a system, direct power taking from the alternating-current side of a power grid is avoided, and therefore the overall performance and cost of an auxiliary power supply are greatly improved on the premise that the electrical safety and control precision are met.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor step-down circuit. Background Technology

[0002] Auxiliary power supply (APS) of a three-phase digital power supply refers to an independent subsystem that derives low-voltage DC power from a three-phase AC system to provide operating voltage for the control, drive, protection, and monitoring units of the main circuit. Traditional three-phase power supply auxiliary power supplies generally draw power directly from the grid side, with the input connected after the three-phase rectifier bridge. They typically include rectification, filtering, and flyback converter circuits. Due to the wide range of grid voltages, their design must cover an input range of 260-680VDC, and the primary-side isolation withstand voltage must meet ≥3 kV to ensure system safety and reliability. However, traditional three-phase power supply auxiliary power supplies require the selection of higher voltage-rated components for high-voltage and wide-range input designs. The transformer in the flyback circuit is relatively large. Since the input current must constantly pass through the rectifier bridge during operation, the rectifier diodes suffer significant losses, resulting in an overall efficiency of only 75%–85%, which is unsuitable for low-power or high-power-density applications.

[0003] For applications requiring low-power three-phase digital power supplies, traditional auxiliary power supplies are no longer sufficient in terms of efficiency, cost, and structural complexity. To achieve higher energy efficiency, lower cost, and a more compact system structure, it is necessary to research an auxiliary power supply circuit with a narrower input range, lower isolation withstand voltage requirements, and higher energy conversion efficiency. Summary of the Invention

[0004] To address the shortcomings of existing circuits, this invention proposes a three-phase digital power supply auxiliary power supply structure based on a resistor-capacitor step-down circuit. This structure efficiently extracts power from the existing DC bus or a specific potential point within the system, replacing the traditional method of directly drawing power from the AC side of the power grid. This significantly improves the overall performance of the auxiliary power supply while ensuring electrical safety and control accuracy, and effectively reduces system costs.

[0005] The technical solution adopted in this invention is: a three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor step-down circuit, comprising: Three-phase power supply, RC step-down circuit, Buck circuit, LDO circuit, control circuit, drive circuit, flyback circuit, three-phase PFC module and three-phase PFC DC bus; The resistor-capacitor step-down circuit is connected to the Buck circuit and the drive circuit, respectively; the three-phase PFC DC bus is connected to the flyback circuit; and the flyback circuit is connected to the Buck circuit and the drive circuit, respectively.

[0006] In a preferred embodiment of the present invention, it further includes: a three-phase power input detection circuit, wherein the input terminal of the three-phase power input detection circuit is connected to the three-phase power supply, and the output terminal of the three-phase power input detection circuit is connected to the control terminal of the LDO circuit.

[0007] In a preferred embodiment of the present invention, the resistor-capacitor step-down circuit includes: a unidirectional rectifier circuit, a first resistor-capacitor step-down circuit, a first resistor-capacitor step-down control circuit, and a first resistor-capacitor step-down output circuit; the output terminal of the unidirectional rectifier circuit is connected to the first resistor-capacitor step-down circuit, and the output terminal of the first resistor-capacitor step-down control circuit is connected to the output terminal of the first resistor-capacitor step-down circuit and the input terminal of the first resistor-capacitor step-down output circuit, respectively.

[0008] In a preferred embodiment of the present invention, the first resistor-capacitor step-down control circuit includes: capacitors C1, C2, C6, C7; resistors R1 to R19, resistors R23 to R35, resistor R40, resistors R43 to R45; MOSFETs Q1 and Q2; and diodes D5, D7, and D8. R19, R29, and R40 are connected in series, with their two ends connected in parallel with C1 and C2. The common upper end of the parallel connection of C6 and C7 is connected to the common lower end of C1 and C2. R1, R7, R13, R23, R30, R2, R8, R14, R24, R31, R3, R9, R15, R25, and R32 constitute a first resistor array. The input terminal of the resistor array is connected to the upper end of R19, and the output terminal of the first resistor array is connected to the drain of Q1; D7 is connected in parallel between the gate and source of Q1; R4, R10, R16, R26, R33, R5, R11, R17, R27, R34, R6, R12, R18, R28, and R35 constitute the second resistor array; the input terminal of the second resistor array is connected to the source of Q1; the output terminal of the second resistor array is connected to the drain of Q2; D8 is connected in parallel between the gate and source of Q2; the source of Q2 is connected to the positive terminal of D5; R43, R44, and R45 are connected in series and their two ends are connected to the gates of Q1 and Q2.

[0009] In a preferred embodiment of the present invention, the first RC step-down control circuit includes: resistors R46 and R47, diode D12, capacitor C9, MOSFET Q6, and diode U3; wherein, the upper end of the parallel connection of R47, D12, and C9 is connected to the lower end of R46 and the gate of Q6, respectively; the drain and source of Q6 are connected in parallel with U3; and the drain of Q6 is connected to the gate of Q2.

[0010] In a preferred embodiment of the present invention, the first RC step-down output circuit includes: capacitors C3, C4, C5, C8; a reference source chip U2; diodes D6, D11; transistors Q3, Q4, Q5; and resistors R20 to R22, R36 to R39, R41, and R42; wherein the upper end of C3 is connected to the negative terminal of D5; the upper end of R20 and R36 connected in series is connected to the positive terminal of C3, the upper end of R21, the upper end of C4, the emitter of Q4, the upper end of R22, and the emitter of Q3; and the lower end of R36 is connected to the lower end of R41. The upper end of R39 is connected to the upper end of C5, the first pin of U2, and the left end of R39; the right end of R39 is connected to the negative terminal of D11; the positive terminal of D11 is connected to the collector of Q4 and the common terminal of R42; the lower end of R42 is connected to the upper end of C8 and the base of Q5; the lower end of C8 is connected to the emitter of Q5, the lower end of C3, the third pin of U2, the lower end of R41, and the lower end of C5; the collector of Q5 is connected to the lower end of R38; the upper end of R38 is connected to the common terminal of R22 and the base of Q3; the collector of Q3 is connected to the positive terminal of D3.

[0011] In a preferred embodiment of the present invention, the resistor-capacitor step-down circuit further includes: a unidirectional rectifier circuit, a second resistor-capacitor step-down circuit, a second resistor-capacitor step-down control circuit, and a second resistor-capacitor step-down output circuit. The output terminal of the unidirectional rectifier circuit is connected to the second resistor-capacitor step-down circuit, and the output terminal of the second resistor-capacitor step-down control circuit is connected to the output terminal of the second resistor-capacitor step-down circuit and the input terminal of the second resistor-capacitor step-down output circuit, respectively.

[0012] In a preferred embodiment of the present invention, the second RC step-down control circuit includes: capacitors C10, C11, C17, C18; resistors R48 to R66, resistors R68 to R84; MOSFETs Q7 and Q8; and diodes D15, D17, and D18. Specifically, the two ends of R66, R74, and R81 are connected in series and in parallel with C10 and C11; the common upper end of the parallel connection of C17 and C18 is connected to the common lower end of C10 and C11; R48, R54, R60, R68, R75, R49, R55, R61, R69, R76, R20, R56, R62, R70, and R77 constitute a third resistor array; the third... The input terminal of the first resistor array is connected to the upper end of R66, and the output terminal of the third resistor array is connected to the drain of Q7; D17 is connected in parallel between the gate and source of Q7; R51, R57, R63, R71, R78, R52, R58, R64, R72, R79, R53, R59, R65, R73, and R80 constitute the fourth resistor array; the input terminal of the fourth resistor array is connected to the source of Q7; the output terminal of the fourth resistor array is connected to the drain of Q8; D18 is connected in parallel between the gate and source of Q8; the source of Q8 is connected to the positive terminal of D15; R82, R83, and R84 are connected in series and their two ends are connected to the gates of Q7 and Q8.

[0013] In a preferred embodiment of the present invention, the second RC step-down control circuit includes: resistors R85 and R86, diode D20, capacitor C19, MOSFET Q10, and diode U4; wherein, the lower end of D20 connected in series with R85 is connected to the upper end of R86, the upper end of C19, and the gate of Q10, respectively; the drain and source of Q10 are connected in parallel with U4; and the drain of Q10 is connected to the gate of Q8.

[0014] In a preferred embodiment of the present invention, the second RC step-down output circuit includes: capacitors C12 and C16, diodes D16 and D19, transistor Q9, and resistor R67; wherein, the common upper end of C12 and C13 connected in parallel is connected to the collector of Q9 and the negative terminal of D15; R67 is connected in parallel to the base and collector of Q9; the base of Q9 is connected to the upper end of D19; the emitter of Q9 is connected to the positive terminal of D16; the upper end of C14, C15, and C16 connected in parallel is connected to the negative terminal of D16; and the lower end of D19 is connected to the lower ends of C12, C13, C14, C15, and C16.

[0015] The beneficial effects of this invention are: 1. The present invention designs a resistor-capacitor step-down circuit to provide stable DC power to each module. Combined with precise voltage threshold control and circuit linkage design, it significantly improves the performance of the auxiliary power supply. 2. Compared to the traditional AC side power supply solution with an efficiency of 70%-80%, it does not require bridge rectification, and the efficiency is improved to over 90%. 3. Output voltage ripple is reduced by approximately 50%, eliminating the need for additional handling of grid fluctuations; overall cost is reduced by 30%. 4. By linking the three-phase optocoupler detection circuit with the LDO enable, the LDO output is automatically turned off when there is no three-phase power input, further improving system reliability; at the same time, the circuit structure is simplified and the size is reduced, taking into account energy efficiency, cost and compactness. Attached Figure Description

[0016] Figure 1 This is a block diagram of the auxiliary power supply circuit for a three-phase digital power supply based on a resistor-capacitor step-down circuit of the present invention; Figure 2 This is a block diagram of a conventional three-phase power supply auxiliary power supply circuit of the present invention; Figure 3 This is the circuit diagram of the resistor-capacitor step-down circuit of the present invention; Figure 4 These are diagrams of flyback and Buck circuits; Figure 5 This is a circuit diagram of a three-phase input signal detection circuit and an LDO circuit. Figure 6 This is the actual circuit diagram of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments. The drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0018] like Figure 2 As shown, in a traditional three-phase power supply auxiliary power system, each module directly obtains energy from the AC power supply side to provide low-voltage power to each module. Each module includes: control circuit, drive circuit, etc. However, it has obvious defects: low efficiency, need to meet high withstand voltage requirements, and is greatly affected by input voltage fluctuations. At the same time, it increases the system cost and is prone to electromagnetic interference, requiring additional design of filter circuits and wide input adaptation circuits. The circuit of this invention is improved based on these purposes.

[0019] like Figure 1 As shown, a three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor (RC) step-down circuit includes: three-phase power, an RC step-down circuit, a Buck circuit, an LDO circuit, a control circuit, a drive circuit, a flyback circuit, a three-phase power input detection circuit, a three-phase PFC module, and a three-phase PFC DC bus. The three-phase power is connected to the RC step-down circuit and the three-phase power input detection circuit respectively. The output terminal of the RC step-down circuit is connected to the Buck circuit and the drive circuit respectively. The output terminal of the Buck circuit is connected sequentially to the LDO circuit, the control circuit, the three-phase PFC module, the three-phase PFC DC bus, and the flyback circuit. The output terminal of the flyback circuit is connected to the Buck circuit and the drive circuit respectively. The drive circuit is connected to the three-phase PFC module. The resistor-capacitor step-down circuit provides the start-up voltage for the Buck circuit, LDO circuit, control circuit, and three-phase PFC module; the operating voltage for the drive circuit and Buck circuit is provided by the flyback circuit. contrast Figure 2 The traditional three-phase power supply auxiliary power system, the present invention and Figure 2 The differences include: 1. The starting voltage (low voltage) of the entire circuit is provided by the RC step-down circuit, while the operating voltage of the drive circuit and buck circuit is still provided by the flyback circuit; and Figure 2 The original system's startup voltage and operating voltage were both provided by the flyback circuit; 2. The start-up voltage of the flyback circuit is provided by the three-phase PFC DC bus, while Figure 2 The startup voltage of the original system's flyback circuit is provided by the bridge rectifier circuit; like Figure 1As shown, the circuit operation of this invention is as follows: Three-phase power is first connected to a resistor-capacitor step-down circuit; this circuit is designed with two independent outputs (output terminal 1 and output terminal 2, respectively); after the system is powered on, output terminal 1 charges its output capacitor; when the capacitor voltage reaches the 30V threshold, this output terminal starts to supply power to the subsequent Buck circuit; after the Buck circuit reduces the voltage to 15V, it is sent to the LDO circuit, and finally the LDO circuit generates a 3.3V voltage to power the control circuit; at the same time, output terminal 2 also charges its output capacitor; when the capacitor voltage reaches 20V, this output terminal directly supplies power to the drive circuit.

[0020] After the control and drive circuits start up and operate normally under the power supply of the RC step-down circuit, the three-phase PFC module begins to run, and its output three-phase PFC DC bus voltage rises accordingly. When the bus voltage reaches the 90V startup threshold, the flyback circuit is activated and begins to take over the power supply task. The flyback circuit also has two outputs (output terminal 1 and output terminal 2): ​​output terminal 1 outputs 30V to power the Buck circuit and simultaneously sends a control signal to stop output terminal 1 of the RC step-down circuit from charging the output capacitor; output terminal 2 outputs 20V to power the drive circuit and simultaneously sends a control signal to stop output terminal 2 of the RC step-down circuit from charging. Through this mechanism, a seamless switch from the startup stage (RC step-down power supply) to the steady-state operation stage (flyback circuit power supply) is achieved.

[0021] like Figure 3 The diagram shows a resistor-capacitor (RC) step-down voltage circuit. The three-phase input provides 380V AC power, and includes: a unidirectional rectifier circuit, an RC step-down main circuit, an RC step-down control circuit, and an output terminal. The three-phase power enters the main circuit after half-wave rectification by the unidirectional rectifier circuit. Taking the branch corresponding to output terminal 1 of the RC step-down circuit as an example: C1, C2, C6, C7 The circuit acts as a filter; R19, R29, and R40 are the gate resistors of switching transistor Q1, serving as current limiting and voltage dividers; R43, R44, and R45 are the gate resistors of switching transistor Q2, with the same function as the gate resistor of Q1; Q1 and Q2 work together to control the on / off state of this branch; D7 and D8 are Zener diodes, providing overvoltage protection for the gates of Q1 and Q2; the resistor arrays R1-R32 and R4-R35 serve as current shunting and voltage reduction; D5 provides current reverse current protection; the working logic of the RC voltage reduction control circuit (corresponding to output terminal 1): the 30V reference voltage is divided by R46 and R47 and then connected to the gate of switching transistor Q6; when the gate voltage of Q6 is lower than 30V, Q6 is turned off, the gates of Q1 and Q2 are at a high level, the branch is turned on, and the RC voltage reduction circuit charges the pre-charge capacitor C3; when the gate voltage of Q6 is ≥30V, Q6 is turned on, and Q1 and Q2... When the gate is low, the branch is turned off, and charging stops. Voltage control at output terminal 1 of the RC step-down circuit: C3 is a pre-charge capacitor, which is charged by the preceding circuit; when the voltage of C3 is >30V, the switching transistor Q3 turns on and discharges to the subsequent stage (because the load of the control circuit is large, the voltage of C3 will continue to drop); when the voltage of C3 is <30V, Q3 turns off and C3 returns to the pre-charge state. Voltage control at output terminal 2 of the RC step-down circuit: C12 is a pre-charge capacitor, which is charged by the preceding circuit; because the load of the drive circuit is small, the voltage of C12 will still rise after the switching transistor Q9 is turned on, and finally the voltage is stabilized at 20V through the Zener diode D19.

[0022] like Figure 4 The diagram shows the coordinated operation of the flyback circuit and the Buck circuit. When the drive circuit and control circuit are started by the RC step-down circuit, the voltage VBUS of the three-phase PFC DC bus continues to rise. When VBUS reaches the 90V threshold, the flyback circuit starts.

[0023] The flyback circuit outputs 30V from output terminal 1 to power the subsequent Buck circuit, while simultaneously turning off Q6 (the control transistor corresponding to output terminal 1) of the RC step-down circuit, cutting off the charging branch of the preceding stage; the Buck circuit steps down the 30V input voltage to 15V to power the subsequent LDO circuit.

[0024] After the flyback circuit outputs 20V from output terminal 2, Q11 turns on to power the subsequent drive circuit. At the same time, it controls Q10 (the control transistor corresponding to output terminal 2) of the RC step-down circuit to turn off, cutting off the charging branch of the previous stage. The flyback circuit replaces the RC step-down circuit with a stable output, which significantly improves the power supply efficiency and stability.

[0025] like Figure 5 The diagram shows the linkage logic between the three-phase power input signal detection circuit and the LDO circuit. The three-phase power inputs AC1, AC2, and AC3 are rectified by the three-phase full-wave rectifier (D28-D40) to output DC power, which is then filtered by capacitor C36. R102, R103, R104, R105, and R106 act as current limiters. U6 in this circuit is an optocoupler, serving as the core for detecting the presence of three-phase power: when there is no three-phase power input, the secondary side of the optocoupler is turned off, the gate of the switching transistor Q12 is at a high level, Q12 conducts, making the enable signal 3.3V_EN low, the LDO circuit does not work, and the subsequent stage stops outputting 3.3V; when there is three-phase power input, the secondary side of the optocoupler conducts, the gate of Q12 is at a low level, Q12 is turned off, 3.3V_EN is high, the LDO circuit works, and the subsequent stage stably outputs 3.3V.

[0026] The present invention Figure 1 and Figure 2 A cost comparison is shown in Table 1: Table 1. Cost Comparison of the Invention and Existing Systems

[0027] Compared to Figure 2 The present invention utilizes a traditional auxiliary power supply that draws power directly from the three-phase AC side (with an efficiency typically of 70%-80%). Figure 2 The circuit (started via a RC step-down circuit and powered from the DC output side) has significant advantages: the equipment does not need to go through a bridge rectifier during operation, and the efficiency can be increased to over 90%; the power source is a stable DC power supply, and the output voltage ripple is reduced by about 50%, eliminating the need for additional adaptation to grid fluctuations or interference; as shown in Table 1, the overall cost is reduced by about 30%, while also helping to reduce the size of the power supply system, simplify circuit design, and significantly improve reliability and operating efficiency. Figure 6 This is the actual circuit diagram of the present invention.

[0028] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor step-down circuit, characterized in that, include: Three-phase power supply, RC step-down circuit, Buck circuit, LDO circuit, control circuit, drive circuit, flyback circuit, three-phase PFC module and three-phase PFC DC bus; The resistor-capacitor step-down circuit is connected to the Buck circuit and the drive circuit, respectively; the three-phase PFC DC bus is connected to the flyback circuit; and the flyback circuit is connected to the Buck circuit and the drive circuit, respectively.

2. The three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor step-down circuit according to claim 1, characterized in that, The resistor-capacitor (RC) step-down circuit includes: a unidirectional rectifier circuit, a first RC step-down circuit, a first RC step-down control circuit, and a first RC step-down output circuit; the output terminal of the unidirectional rectifier circuit is connected to the first RC step-down circuit, and the output terminal of the first RC step-down control circuit is connected to the output terminal of the first RC step-down circuit and the input terminal of the first RC step-down output circuit, respectively.

3. The three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor step-down circuit according to claim 2, characterized in that, The first RC step-down control circuit includes: capacitors C1, C2, C6, and C7; resistors R1 to R19, R23 to R35, R40, and R43 to R45; MOSFETs Q1 and Q2; and diodes D5, D7, and D8. R19, R29, and R40 are connected in series, with their two ends connected in parallel with C1 and C2. The common upper terminal of the parallel connection between C6 and C7 is connected to the common lower terminal of C1 and C2. R1, R7, R13, R23, R30, R2, R8, R14, R24, R31, R3, R9, R15, R25, and R32 constitute the first resistor array. The input of the first resistor array... The first resistor array is connected to the upper end of R19, and the output end of the first resistor array is connected to the drain of Q1; D7 is connected in parallel between the gate and source of Q1; R4, R10, R16, R26, R33, R5, R11, R17, R27, R34, R6, R12, R18, R28, and R35 form the second resistor array; the input end of the second resistor array is connected to the source of Q1; the output end of the second resistor array is connected to the drain of Q2; D8 is connected in parallel between the gate and source of Q2; the source of Q2 is connected to the positive terminal of D5; R43, R44, and R45 are connected in series and their two ends are connected to the gates of Q1 and Q2.

4. The three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor step-down circuit according to claim 3, characterized in that, The first RC step-down control circuit includes: resistors R46 and R47, diode D12, capacitor C9, MOSFET Q6, and diode U3; wherein, the upper end of the parallel connection of R47, D12, and C9 is connected to the lower end of R46 and the gate of Q6, respectively; the drain and source of Q6 are connected in parallel with U3; and the drain of Q6 is connected to the gate of Q2.

5. The three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor step-down circuit according to claim 4, characterized in that, The first RC step-down output circuit includes: capacitors C3, C4, C5, and C8; a reference source chip U2; diodes D6 and D11; transistors Q3, Q4, and Q5; and resistors R20 to R22, R36 to R39, R41, and R42. The upper end of C3 is connected to the negative terminal of D5. The upper ends of R20 and R36 (connected in series) are connected to the positive terminal of C3, the upper end of R21, the upper end of C4, the emitter of Q4, the upper end of R22, and the emitter of Q3. The lower end of R36 is connected to the upper end of R41 and the upper end of C5. Connect pin 1 of U2 to the left end of R39; connect the right end of R39 to the negative terminal of D11; connect the positive terminal of D11 to the collector of Q4 and the common terminal of R42; connect the lower end of R42 to the upper end of C8 and the base of Q5; connect the lower end of C8 to the emitter of Q5, the lower end of C3, pin 3 of U2, the lower end of R41, and the lower end of C5; connect the collector of Q5 to the lower end of R38; connect the upper end of R38 to the common terminal of R22 and the base of Q3; connect the collector of Q3 to the positive terminal of D3.

6. The three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor step-down circuit according to claim 1, characterized in that, The resistor-capacitor (RC) step-down circuit also includes: a unidirectional rectifier circuit, a second RC step-down circuit, a second RC step-down control circuit, and a second RC step-down output circuit. The output terminal of the unidirectional rectifier circuit is connected to the second RC step-down circuit, and the output terminal of the second RC step-down control circuit is connected to the output terminal of the second RC step-down circuit and the input terminal of the second RC step-down output circuit, respectively.

7. The three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor step-down circuit according to claim 6, characterized in that, The second RC step-down control circuit includes: capacitors C10, C11, C17, and C18; resistors R48 to R66 and R68 to R84; MOSFETs Q7 and Q8; and diodes D15, D17, and D18. R66, R74, and R81 are connected in series, with their ends connected in parallel with C10 and C11. The common upper terminal of the parallel connection of C17 and C18 is connected to the common lower terminal of C10 and C11. R48, R54, R60, R68, R75, R49, R55, R61, R69, R76, R20, R56, R62, R70, and R77 form a third resistor array. The input terminal of the third resistor array... The upper end of R66 is connected to the third resistor array, and the output end of the third resistor array is connected to the drain of Q7; D17 is connected in parallel between the gate and source of Q7; R51, R57, R63, R71, R78, R52, R58, R64, R72, R79, R53, R59, R65, R73, and R80 form the fourth resistor array; the input end of the fourth resistor array is connected to the source of Q7; the output end of the fourth resistor array is connected to the drain of Q8; D18 is connected in parallel between the gate and source of Q8; the source of Q8 is connected to the positive terminal of D15; R82, R83, and R84 are connected in series and their two ends are connected to the gates of Q7 and Q8.

8. The three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor step-down circuit according to claim 7, characterized in that, The second RC step-down control circuit includes: resistors R85 and R86, diode D20, capacitor C19, MOSFET Q10, and diode U4; wherein, the lower end of D20 connected in series with R85 is connected to the upper end of R86, the upper end of C19, and the gate of Q10 respectively; the drain and source of Q10 are connected in parallel with U4; the drain of Q10 is connected to the gate of Q8.

9. The three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor step-down circuit according to claim 8, characterized in that, The second RC step-down output circuit includes: capacitors C12 to C16, diodes D16 and D19, transistor Q9, and resistor R67; wherein, the common upper end of C12 and C13 connected in parallel is connected to the collector of Q9 and the negative terminal of D15; R67 is connected in parallel to the base and collector of Q9; the base of Q9 is connected to the upper end of D19; the emitter of Q9 is connected to the positive terminal of D16; the upper end of C14, C15, and C16 connected in parallel is connected to the negative terminal of D16; and the lower end of D19 is connected to the lower ends of C12, C13, C14, C15, and C16.

10. The three-phase digital power supply auxiliary power supply circuit based on a resistor-capacitor step-down circuit according to claim 1, characterized in that, Also includes: The three-phase power input detection circuit has its input terminal connected to the three-phase power supply and its output terminal connected to the control terminal of the LDO circuit.

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