Subway escalator signal line interference elimination circuit and implementation method

Abstract

The invention discloses a subway escalator signal line interference elimination circuit and an implementation method, and the circuit comprises a 24V signal control source which is used for providing a power supply; the AC coupling interference signal is used for providing a 50Hz AC signal; the rectifier bridge is used for shaping the induced alternating current signal into direct current voltage; the LCR filtering module is used for converting into a stable direct-current power supply; the step-down diode is used for reducing the voltage of the direct-current signal; the voltage stabilizer is used for converting a 24V direct current power supply into a 5V direct current power supply; the DC-DC Buck conversion circuit is used for supplying power to the single chip microcomputer U2; the single chip microcomputer U2 is used for judging whether the sensed signal is an interference signal or a normal 24V control signal; and the switch MOS tube is used for controlling the on-off of a control power supply of the LED indicating lamp. According to the invention, interference signals can be effectively detected, and the interference signals can be actively blocked; under the control of a normal signal, the circuit system ensures that the LED indicating lamp of the IBP can output normally.

Description

Technical Field

[0001] The invention belongs to the technical field of elevators, and in particular relates to a subway escalator signal line interference elimination circuit and an implementation method thereof. Background Art

[0002] Figure 1 This is the current system wiring diagram of the IBP in the subway control room. The LED indicator on the IBP panel is directly controlled by the relay of the escalator control box. The relay controls the on and off of the DC 24V as the power supply of the LED indicator. Since the distance from the terminal box of the escalator control box to the IBP panel is generally several dozen meters, and this high-voltage line is mixed in the subway electrical system, when passing through the strong power line, the control line of the IBP indicator will sense the AC signal of the power frequency. After actual measurement, the amplitude of the power frequency coupled AC signal fluctuates between 0 and ±30V. Since the IBP indicator is an LED device, it is sensitive to current. The milliampere level current will cause the LED to flash weakly, causing false indications. Due to the interference of the subway's strong power system, the subway escalator control system will cause the IBP LED indicator to cause virtual flickering when no control signal is issued, causing some LED lamp beads to be damaged after a long time.

[0003] Therefore, a subway escalator signal line interference elimination circuit and implementation method are urgently needed. Summary of the invention

[0004] In order to solve the defects of the prior art, the present invention provides a subway escalator signal line interference elimination circuit and an implementation method.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] The present invention provides a subway escalator signal line interference elimination circuit, comprising:

[0007] 24V signal control source, used to provide power to the LED indicator light;

[0008] AC coupled interference signal, used to provide a 50Hz AC signal with an amplitude of 0~40VAC;

[0009] A rectifier bridge is used to shape the induced AC signal into a DC voltage;

[0010] LCR filter module, used to convert the shaped waveform into a stable DC power supply;

[0011] The step-down diode is used to step down the DC signal to ensure that when the sensed DC voltage is lower than 5V, it prevents the LED indicator from dimming due to system malfunction before the microcontroller fails to work properly;

[0012] The voltage stabilizer is used to convert the 24V DC power supply into 5V DC power to provide stable power to the LED indicator to prevent flickering;

[0013] The DC-DC Buck conversion circuit is used to convert the induced DC power into 3.3V to power the microcontroller U2;

[0014] The single-chip computer U2 is used to determine whether the induced signal is an interference signal or a normal 24V control signal, thereby controlling whether the switch MOS tube is turned on and obtaining a stable voltage source for the LED indicator light;

[0015] The switch MOS tube is used to control the on and off of the control power supply of the LED indicator.

[0016] Preferably, the rectifier bridge includes a second rectifier diode D2, a third rectifier diode D3, a sixth rectifier diode D6 and a seventh rectifier diode D7, the anode of the second rectifier diode D2 and the cathode of the third rectifier diode D3 are electrically connected to JP1.1 of the 24V signal control source, the anode of the sixth rectifier diode D6 and the cathode of the seventh rectifier diode D7 are electrically connected to JP1.3 of the 24V signal control source, the cathodes of the second rectifier diode D2 and the sixth rectifier diode D6 are electrically connected to the first end of the first resistor R1, and the anodes of the third rectifier diode D3 and the seventh rectifier diode D7 are grounded; the rectifier bridge converts the induced alternating current into forward direct current through the second rectifier diode D2, the third rectifier diode D3, the sixth rectifier diode D6 and the seventh rectifier diode D7.

[0017] Preferably, the LCR filter module includes a first resistor R1, a third resistor R3, a fourth resistor R4, a first inductor L1, a first capacitor C1, a second capacitor C2, and a bidirectional voltage regulator D5. The first end of the first resistor R1 is electrically connected to the first end of the third resistor R3, and the second end of the third resistor R3 is electrically connected to the first end of the fourth resistor R4; the second end of the first resistor R1 is electrically connected to the first end of the first inductor L1 and the first end of the bidirectional voltage regulator D5 through a protector F1, the second end of the first inductor L1 is electrically connected to the first end of the first capacitor C1 and the first end of the second capacitor C2, and the fourth resistor R4, the bidirectional voltage regulator D5, the first end of the first capacitor C1, and the second end of the second capacitor C2 are grounded; after the signal passes through the LCR filter module, the induced virtual electric energy decreases, thereby reducing the induced voltage value.

[0018] Preferably, the cathode of the buck diode is electrically connected to the second end of the first inductor L1, the anode of the buck diode is electrically connected to IN of the regulator, and OUT of the regulator is electrically connected to the second end of the sixth resistor R6 and the source of the PMOS tube Q1.

[0019] Preferably, the DC-DC Buck conversion circuit includes a DC-DC Buck power chip XL1, a fifth capacitor C5, a sixth capacitor C6, a seventh capacitor C7, an eighth capacitor C8, a voltage regulator diode D8, a second inductor L2, an eighth resistor R8, and a tenth resistor R10. Pin 1 of the DC-DC Buck power chip XL1, a first end of the fifth capacitor C5, and a first end of the sixth capacitor C6 are electrically connected to the second end of the first inductor. Pin 4 of the DC-DC Buck power chip XL1 and the second ends of the fifth capacitor C5 and the sixth capacitor C6 are grounded. Pin 2 of the DC-DC Buck power chip XL1 is electrically connected to the cathode of the voltage regulator diode D8 and the first end of the second inductor L2. The second end of the second inductor L2, the first end of the eighth resistor R8, the first end of the seventh capacitor C7, and the first end of the eighth capacitor C8 are connected to Vout1. Pin 3 of the Buck power chip XL1 is electrically connected to the second end of the eighth resistor R8 and the first end of the tenth resistor R10, and the second ends of the Zener diode D8, the tenth resistor R10, the seventh capacitor C7, and the eighth capacitor C8 are grounded; the maximum input voltage of the DC-DC Buck conversion circuit is 100V.

[0020] Preferably, the switch MOS tube includes a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, a ninth resistor R9, a PMOS tube Q1 and an NMOS tube Q2, the first end of the seventh resistor R7 is electrically connected to pin 18 of the single-chip computer U2, the second end of the seventh resistor R7 is electrically connected to the first end of the ninth resistor R9 and the gate of the NMOS tube Q2, the second end of the ninth resistor R9 and the source of the NMOS tube Q2 are grounded, the drain of the NMOS tube Q2 is electrically connected to the first end of the fifth resistor R5, and the second end of the fifth resistor R5 is electrically connected to the first end of the sixth resistor R6 and the gate of the PMOS tube Q1.

[0021] Preferably, pin 7 of the single chip microcomputer U2 is electrically connected to the second end of the third resistor R3 through an A / D conversion module, and is used to monitor the voltage on the signal line in real time through the A / D conversion module.

[0022] The present invention also provides a method for implementing a subway escalator signal line interference elimination circuit, comprising the following steps:

[0023] Step 1: The rectifier bridge shapes the AC signal provided by the AC coupled interference signal into a DC voltage, which becomes a DC steamed wave after shaping;

[0024] Step 2: The shaped DC signal is converted into a stable DC power supply through the LCR filter module, which is used to power the microcontroller U2 and the LED indicator light;

[0025] Step 3: The signal is stepped down through the buck diode. When the voltage of the sensed signal is less than 5V after processing, the voltage regulator will not work, no voltage output, and the LED indicator will not flash; when the voltage of the sensed signal is greater than 5V after processing, the DC-DC Buck module starts to work and outputs 3.3V voltage, and the microcontroller U2 starts to work at this time;

[0026] Step 4: When the single-chip computer U2 is powered on, the voltage output by the rectifier bridge is divided by the sampling resistor and enters the A / D conversion module of the single-chip computer U2. The on and off of the MOS tube is controlled according to the judged input voltage, thereby controlling the on and off of the LED indicator. Specifically, the single-chip computer U2 monitors the voltage on the signal line through the A / D conversion module of the single-chip computer in real time. If the normal 24V control signal is sensed, the switch MOS tube is controlled to be turned on, and the LED indicator lights up; if the interference signal is sensed, the switch MOS tube is turned off, and the LED indicator goes out.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention can effectively detect interference signals and actively block interference signals; and under normal signal control, the circuit system ensures that the LED indicator light of the IBP can output normally. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the control principle diagram of the IBP plate of the subway escalator in the prior art;

[0030] Figure 2 It is a structural block diagram of a subway escalator signal line interference elimination circuit of the present invention;

[0031] Figure 3 It is a working flow chart of a method for realizing a subway escalator signal line interference elimination circuit of the present invention;

[0032] Figure 4 The invention discloses a circuit schematic diagram of a subway escalator signal line interference elimination circuit. DETAILED DESCRIPTION

[0033] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0034] like Figure 2 , Figure 4 As shown, in this embodiment, a subway escalator signal line interference elimination circuit is provided, comprising:

[0035] 24V signal control source 1, used to provide power to the LED indicator light 10;

[0036] AC coupled interference signal 2 is used to provide a 50Hz AC signal with an amplitude of 0 to 40VAC;

[0037] A rectifier bridge 3, used to shape the induced AC signal into a DC voltage;

[0038] LCR filter module 4, used to convert the shaped waveform into a stable DC power supply;

[0039] The step-down diode 5 is used to step down the DC signal to ensure that when the sensed DC voltage is lower than 5V, the LED indicator 10 is prevented from dimming due to system malfunction before the single chip microcomputer fails to work properly;

[0040] A voltage stabilizer 6 is used to convert the 24V DC power supply into 5V DC power to provide a stable power supply to the LED indicator 10 to prevent flickering;

[0041] A DC-DC Buck conversion circuit 7 is used to convert the induced DC power into 3.3V to supply power to the microcontroller U28;

[0042] The single chip microcomputer U28 is used to determine whether the induced signal is an interference signal or a normal 24V control signal, thereby controlling whether the switch MOS tube 9 is turned on, and obtaining a stable voltage source for the LED indicator light 10;

[0043] The switch MOS tube 9 is used to control the on and off of the control power supply of the LED indicator light 10 .

[0044] In this embodiment, the rectifier bridge 3 includes a second rectifier diode D2, a third rectifier diode D3, a sixth rectifier diode D6 and a seventh rectifier diode D7, the anode of the second rectifier diode D2 and the cathode of the third rectifier diode D3 are electrically connected to JP1.1 of the 24V signal control source 1, the anode of the sixth rectifier diode D6 and the cathode of the seventh rectifier diode D7 are electrically connected to JP1.3 of the 24V signal control source 1, the cathodes of the second rectifier diode D2 and the sixth rectifier diode D6 are electrically connected to the first end of the first resistor R1, and the anodes of the third rectifier diode D3 and the seventh rectifier diode D7 are grounded; the rectifier bridge 3 converts the induced alternating current into forward direct current through the second rectifier diode D2, the third rectifier diode D3, the sixth rectifier diode D6 and the seventh rectifier diode D7.

[0045] In this embodiment, the LCR filter module 4 includes a first resistor R1, a third resistor R3, a fourth resistor R4, a first inductor L1, a first capacitor C1, a second capacitor C2, and a bidirectional voltage regulator D5. The first end of the first resistor R1 is electrically connected to the first end of the third resistor R3, and the second end of the third resistor R3 is electrically connected to the first end of the fourth resistor R4; the second end of the first resistor R1 is electrically connected to the first end of the first inductor L1 and the first end of the bidirectional voltage regulator D5 through a protector F1, the second end of the first inductor L1 is electrically connected to the first end of the first capacitor C1 and the first end of the second capacitor C2, and the fourth resistor R4, the bidirectional voltage regulator D5, the first end of the first capacitor C1, and the second end of the second capacitor C2 are grounded; after the signal passes through the LCR filter module 4, the induced virtual electric energy decreases, thereby reducing the induced voltage value.

[0046] In this embodiment, the cathode of the buck diode 5 is electrically connected to the second end of the first inductor L1, the anode of the buck diode 5 is electrically connected to IN of the regulator 6, and the OUT of the regulator 6 is electrically connected to the second end of the sixth resistor R6 and the source of the PMOS tube Q1.

[0047] In this embodiment, the DC-DC Buck conversion circuit 7 includes a DC-DC Buck power chip XL1, a fifth capacitor C5, a sixth capacitor C6, a seventh capacitor C7, an eighth capacitor C8, a voltage regulator diode D8, a second inductor L2, an eighth resistor R8, and a tenth resistor R10. Pin 1 of the DC-DC Buck power chip XL1, a first end of the fifth capacitor C5, and a first end of the sixth capacitor C6 are electrically connected to the second end of the first inductor. Pin 4 of the DC-DC Buck power chip XL1 and the second ends of the fifth capacitor C5 and the sixth capacitor C6 are grounded. Pin 2 of the DC-DC Buck power chip XL1 is electrically connected to the cathode of the voltage regulator diode D8 and the first end of the second inductor L2. The second end of the second inductor L2, the first end of the eighth resistor R8, the first end of the seventh capacitor C7, and the first end of the eighth capacitor C8 are connected to Vout1. Pin 3 of the Buck power chip XL1 is electrically connected to the second end of the eighth resistor R8 and the first end of the tenth resistor R10, and the second ends of the Zener diode D8, the tenth resistor R10, the seventh capacitor C7, and the eighth capacitor C8 are grounded; the maximum input voltage of the DC-DC Buck conversion circuit 7 is 100V.

[0048] In this embodiment, the switch MOS tube 9 includes a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, a ninth resistor R9, a PMOS tube Q1 and an NMOS tube Q2. The first end of the seventh resistor R7 is electrically connected to pin 18 of the single-chip computer U28, the second end of the seventh resistor R7 is electrically connected to the first end of the ninth resistor R9 and the gate of the NMOS tube Q2, the second end of the ninth resistor R9 and the source of the NMOS tube Q2 are grounded, the drain of the NMOS tube Q2 is electrically connected to the first end of the fifth resistor R5, and the second end of the fifth resistor R5 is electrically connected to the first end of the sixth resistor R6 and the gate of the PMOS tube Q1.

[0049] In this embodiment, the pin 7 of the single chip microcomputer U28 is electrically connected to the second end of the third resistor R3 through the A / D conversion module, and is used to monitor the voltage on the signal line in real time through the A / D conversion module.

[0050] like Figure 3 As shown, this embodiment also provides a method for implementing a subway escalator signal line interference elimination circuit, comprising the following steps:

[0051] (1) The 24V signal control source JP1.1 and JP1.3 of the LED indicator light inputs the signal line interference elimination circuit. At the same time, the AC coupling interference signal induced on the transmission cable will also be superimposed and enter. The voltage range of the AC interference signal is ±30V.

[0052] (2) When the subway escalator control box outputs the LED indicator light off, JP1.1 and JP1.3 have no +24V voltage. At this time, there is only the AC coupling interference signal induced on the transmission cable. Since the amplitude of the AC coupling interference signal is related to the actual magnetic field environment, if the signal is weak, after passing through the second rectifier diode D2, the third rectifier diode D3, the sixth rectifier diode D6, the seventh rectifier diode D7, and the LCR filter module, when the VIN output voltage is between 0 and 5V, the DC-DC Buck power supply chip XL1 does not reach the start-up working voltage, and the output voltage Vout1 is 0; the single-chip computer U2 is not working. VIN2 = VIN-5V, the voltage input to the regulator U1 is 0, so the Vout2 output is zero. When the single-chip computer is not working, the power supply voltage of the LED indicator light is 0V, and the LED light is off and will not flash.

[0053] (3) When the AC coupling interference signal induced on the transmission cable is strong, if VIN is greater than 5V, the DC-DC Buck power chip XL1 reaches the start-up operating voltage. At this time, the output voltage Vout1 is 3.3V. At this time, the ARM microcontroller U2 works normally and Vout2 also has an output voltage.

[0054] (4) When the microcontroller U2 is working normally, the processing logic is as follows Figure 3 As shown, the single-chip computer U2 will always monitor the input voltage value of VIN_ADC. If the monitoring detects a steamed wave with a frequency change, it means that this is an AC coupling interference signal induced on the transmission cable, and the control signal 24V is not output. At this time, the single-chip computer U2 will output a high level to turn on the NMOS tube Q2 and turn off the PMOS tube Q1. The output voltage of 5V_LED is 0. At this time, the BP LED indicator light is completely off, avoiding the previous flickering phenomenon.

[0055] (5) When the single-chip microcomputer U2 monitors a stable 24V input, it is judged as a normal control signal input. The single-chip microcomputer U2 outputs a low level, turning off the NMOS tube Q2 and turning on the PMOS tube Q1. The output voltage of 5V_LED is 5V. At this time, the LED indicator light is fully lit, and the system works normally without flickering.

[0056] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A subway escalator signal line interference elimination circuit, characterized in that: include: A 24V signal control source (1) is used to provide power to the LED indicator light (10); AC coupled interference signal (2), used to provide a 50Hz AC signal with an amplitude of 0 to 40VAC; A rectifier bridge (3) for shaping the induced AC signal into a DC voltage; An LCR filter module (4) for converting the shaped waveform into a stable DC power supply; The step-down diode (5) is used to step down the voltage of the DC signal to ensure that when the sensed DC voltage is lower than 5V, the LED indicator (10) is prevented from dimming due to system malfunction before the single chip computer fails to work normally; A voltage stabilizer (6) is used to convert the 24V DC power supply into 5V DC power to provide a stable power supply to the LED indicator (10) to prevent flickering; A DC-DC Buck conversion circuit (7) is used to convert the induced direct current into 3.3V to power the microcontroller U2 (8); The single chip computer U2 (8) is used to determine whether the sensed signal is an interference signal or a normal 24V control signal, thereby controlling whether the switch MOS tube (9) is turned on, so as to obtain a stable voltage source for the LED indicator light (10); The switch MOS tube (9) is used to control the on and off of the control power supply of the LED indicator light (10).

2. The subway escalator signal line interference elimination circuit according to claim 1, characterized in that: The rectifier bridge (3) comprises a second rectifier diode D2, a third rectifier diode D3, a sixth rectifier diode D6 and a seventh rectifier diode D7; the anode of the second rectifier diode D2 and the cathode of the third rectifier diode D3 are electrically connected to JP1.1 of the 24V signal control source (1); the anode of the sixth rectifier diode D6 and the cathode of the seventh rectifier diode D7 are electrically connected to JP1.3 of the 24V signal control source (1); the cathodes of the second rectifier diode D2 and the sixth rectifier diode D6 are electrically connected to the first end of the first resistor R1; the anodes of the third rectifier diode D3 and the seventh rectifier diode D7 are grounded; the rectifier bridge (3) converts the induced alternating current into forward direct current through the second rectifier diode D2, the third rectifier diode D3, the sixth rectifier diode D6 and the seventh rectifier diode D7.

3. The subway escalator signal line interference elimination circuit according to claim 2, characterized in that: The LCR filter module (4) comprises a first resistor R1, a third resistor R3, a fourth resistor R4, a first inductor L1, a first capacitor C1, a second capacitor C2, and a bidirectional voltage regulator D5; the first end of the first resistor R1 is electrically connected to the first end of the third resistor R3, and the second end of the third resistor R3 is electrically connected to the first end of the fourth resistor R4; the second end of the first resistor R1 is electrically connected to the first end of the first inductor L1 and the first end of the bidirectional voltage regulator D5 through a protector F1; the second end of the first inductor L1 is electrically connected to the first end of the first capacitor C1 and the first end of the second capacitor C2; the fourth resistor R4, the bidirectional voltage regulator D5, the first end of the first capacitor C1, and the second end of the second capacitor C2 are grounded; after the signal passes through the LCR filter module (4), the induced virtual electric energy is reduced, thereby reducing the induced voltage value.

4. The subway escalator signal line interference elimination circuit according to claim 3, characterized in that: The cathode of the step-down diode (5) is electrically connected to the second end of the first inductor L1, the anode of the step-down diode (5) is electrically connected to the IN of the voltage regulator (6), and the OUT of the voltage regulator (6) is electrically connected to the second end of the sixth resistor R6 and the source of the PMOS tube Q1.

5. The subway escalator signal line interference elimination circuit according to claim 4, characterized in that: The DC-DC Buck conversion circuit (7) comprises a DC-DC Buck power chip XL1, a fifth capacitor C5, a sixth capacitor C6, a seventh capacitor C7, an eighth capacitor C8, a voltage stabilizing diode D8, a second inductor L2, an eighth resistor R8, and a tenth resistor R10; pin 1 of the DC-DC Buck power chip XL1, a first end of the fifth capacitor C5, and a first end of the sixth capacitor C6 are electrically connected to the second end of the first inductor; pin 4 of the DC-DC Buck power chip XL1 and the second ends of the fifth capacitor C5 and the sixth capacitor C6 are grounded; pin 2 of the DC-DC Buck power chip XL1 is electrically connected to the cathode of the voltage stabilizing diode D8 and the first end of the second inductor L2; the second end of the second inductor L2, the first end of the eighth resistor R8, the first end of the seventh capacitor C7, and the first end of the eighth capacitor C8 are connected to Vout1; and the DC-DC Pin 3 of the Buck power chip XL1 is electrically connected to the second end of the eighth resistor R8 and the first end of the tenth resistor R10; the second ends of the voltage stabilizing diode D8, the tenth resistor R10, the seventh capacitor C7 and the eighth capacitor C8 are grounded; and the maximum input voltage of the DC-DC Buck conversion circuit (7) is 100V.

6. The subway escalator signal line interference elimination circuit according to claim 5, characterized in that: The switch MOS tube (9) comprises a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, a ninth resistor R9, a PMOS tube Q1 and an NMOS tube Q2. The first end of the seventh resistor R7 is electrically connected to the 18th pin of the single chip computer U2 (8). The second end of the seventh resistor R7 is electrically connected to the first end of the ninth resistor R9 and the gate of the NMOS tube Q2. The second end of the ninth resistor R9 and the source of the NMOS tube Q2 are grounded. The drain of the NMOS tube Q2 is electrically connected to the first end of the fifth resistor R5. The second end of the fifth resistor R5 is electrically connected to the first end of the sixth resistor R6 and the gate of the PMOS tube Q1.

7. The subway escalator signal line interference elimination circuit according to claim 6, characterized in that: Pin 7 of the single chip microcomputer U2 (8) is electrically connected to the second end of the third resistor R3 through the A / D conversion module, and is used to monitor the voltage on the signal line in real time through the A / D conversion module.

8. A method for implementing the subway escalator signal line interference elimination circuit as claimed in any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: The rectifier bridge (3) shapes the AC signal provided by the AC coupled interference signal (2) into a DC voltage, which is a DC steamed wave after shaping; Step 2: The shaped DC signal is converted into a stable DC power supply through the LCR filter module (4), which is used to power the single chip computer U2 (8) and the LED indicator light (10); Step 3: The signal is stepped down by the step-down diode (5). When the voltage of the sensed signal is less than 5V after processing, the voltage regulator (6) will not work, no voltage will be output, and the LED indicator (10) will not flash. When the voltage of the sensed signal is greater than 5V after processing, the DC-DC Buck module (7) starts to work and outputs a voltage of 3.3V. At this time, the single-chip microcomputer U2 (8) starts to work. Step 4: When the single-chip microcomputer U2 (8) is powered on, the voltage output by the rectifier bridge (3) is divided by the sampling resistor and enters the A / D conversion module of the single-chip microcomputer U2 (8). The on and off of the MOS tube is controlled according to the judged input voltage condition, thereby controlling the on and off of the LED indicator (10).

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