A housing access live line protection circuit by ac sampling and auxiliary voltage comparison

Abstract

The utility model relates to a shell access live line protection circuit through AC sampling and auxiliary voltage comparison, include: alternating current wiring terminal, its access the alternating current single -phase commercial power, or, alternating current two -phase double -fire line commercial power, or, alternating current three -phase three -fire line commercial power, bridge rectifier circuit, crystal oscillator Y1, inductance coil T1A and relay KJ, and the pin of relay KJ accesses the shell, and the shell is not electrified through the control of relay. The utility model discloses when the customer terminal ground wire access live line, through the protection circuit control relay (normally open) disconnect the connection between the earth and the shell, eliminates the harm of shell electrification to human body.

Description

Technical Field

[0001] This utility model relates to the field of circuit protection technology, specifically to a housing-connected live wire protection circuit that uses AC sampling and auxiliary transformer voltage comparison. Background Technology

[0002] When using electricity on the user side, if the circuit protection function is not good, the user terminal equipment may cause injury to the human body due to the casing becoming electrified. Therefore, it is necessary to design a protection circuit for the casing of the user terminal equipment, which can prevent the casing from becoming electrified through circuit control, so as to prevent electric shock injury to the human body. Utility Model Content

[0003] To achieve the above objectives, this utility model provides a casing-connected live wire protection circuit that uses AC sampling and auxiliary transformer voltage comparison, and is connected to AC single-phase mains power, or AC two-phase dual-live-wire mains power, or AC three-phase three-live-wire mains power. The live wire protection circuit includes:

[0004] AC terminal block, which is connected to the AC single-phase mains power, or AC two-phase dual-wire mains power, or AC three-phase three-wire mains power;

[0005] A bridge rectifier circuit includes four diodes D1, D2, D3 and D4. The common terminal of D1 and D2 is connected to the L terminal or L1 terminal of the AC terminal block. The common terminal of D1 and D3 is grounded. The common terminal of D3 and D4 is connected to the N terminal or L2 terminal of the AC terminal block.

[0006] Crystal oscillator Y1, one end of which is connected to the common terminal of D2 and D4, and the other end of which is connected to the common terminal of D1 and D3;

[0007] Inductor T1A, its first terminal is connected to the common terminal of D2 and D4, its third terminal is connected to the drain of transistor Q1, and the source of transistor Q1 is grounded;

[0008] One end of capacitor CY1 is connected to the common terminal of D1 and D2, and the other end of capacitor CY1 is connected to one end of resistor R1. The other end of resistor R1 is connected to the positive terminal of diode D8 and one end of resistor R3. The other end of resistor R3 is connected to the PE terminal of the AC terminal.

[0009] One end of capacitor CY2 is connected to the common terminal of D3 and D4, and the other end of capacitor CY2 is connected to one end of resistor R2. The other end of resistor R2 is connected to the positive terminal of diode D7 and one end of resistor R4. The other end of resistor R4 is connected to the PE terminal of the AC terminal.

[0010] The negative terminals of diodes D7 and D8 are connected to the AC1 terminal of the contactor. One end of resistor R5 is connected to the AC1 terminal of the contactor, and the other end of resistor R5 is connected to the PE terminal of the AC terminal. One end of capacitor C3 is connected to the AC1 terminal of the contactor, and the other end of capacitor C3 is connected to the PE terminal of the AC terminal.

[0011] One end of resistor R5 is connected to the AC1 terminal of the contactor, and the other end of resistor R5 is connected to the second terminal of comparator ICA. One end of resistor R6 is connected to ACVREF, and the other end of resistor R5 is connected to the third terminal of comparator ICA. The first terminal of comparator ICA is connected to one end of resistor R7, and the other end of resistor R7 is connected to the ON / OFF switch.

[0012] The relay KJ has its first pin connected to the PE terminal of the AC terminal block, its fourth pin connected to the collector of transistor Q2, the base of transistor Q2 connected to the ON / OFF switch, the emitter of transistor Q2 connected to the PE terminal of the AC terminal block, and its fifth pin connected to the housing.

[0013] Among the possible implementations are:

[0014] Inductor T1B has its fourth terminal connected to the positive terminal of diode D5, its third terminal connected to the PE terminal of the AC terminal block, the negative terminal of diode D5 connected to the VCC terminal and to one end of capacitor C1, and the other end of capacitor C1 connected to the PE terminal of the AC terminal block.

[0015] Among the possible implementations are:

[0016] The inductor T1C has its fourth terminal connected to the positive terminal of diode D6, its third terminal connected to the PE terminal of the AC terminal block, the negative terminal of diode D6 connected to the VCC terminal and to one end of capacitor C2, and the other end of capacitor C2 connected to the PE terminal of the AC terminal block.

[0017] In one possible implementation, when connected to single-phase AC mains power, the L terminal of the AC terminal is connected to the PE terminal of the distribution box, the N terminal of the AC terminal is connected to the N terminal of the distribution box, and the PE terminal of the AC terminal is connected to the L terminal of the distribution box.

[0018] In a possible implementation: when connected to a two-phase dual-live-wire AC mains power supply, the L terminal of the AC terminal is connected to the PE terminal of the distribution box, the N terminal of the AC terminal is connected to the L2 terminal of the distribution box, and the PE terminal of the AC terminal is connected to the L1 terminal of the distribution box.

[0019] In a possible implementation: when connected to a three-phase, three-wire AC mains power supply, the L1 terminal of the AC terminal is connected to the L1 terminal of the distribution box, the L2 terminal of the AC terminal is connected to the L2 terminal of the distribution box, and the PE terminal of the AC terminal is connected to the L3 terminal of the distribution box.

[0020] Among the possible implementations are:

[0021] Comparator U2B has its 5th pin connected to the common terminal of resistors R8 and R9. The other end of resistor R8 is connected to the PE terminal of the AC terminal block, and the other end of resistor R9 is connected to ACVREF. Its 6th pin is connected to the common terminal of resistors R10, R11, and capacitor C4. The other end of resistor R10 is connected to VCC, the other end of resistor R11 is connected to the PE terminal of the AC terminal block, and the other end of capacitor C4 is connected to the PE terminal of the AC terminal block. Its 7th pin is connected to one end of resistor R12.

[0022] Optocoupler U4 has its first end connected to the other end of resistor R12, its second end connected to the PE terminal of the AC terminal block, and its third end connected to one end of R13, with the other end of R13 connected to VCC.

[0023] Comparator U2C has its third pin connected to the common terminal of resistors R14 and R15. The other end of resistor R14 is connected to the PE terminal of the AC terminal block, and the other end of resistor R15 is connected to AC1. Its second pin is connected to the common terminal of resistors R16, R17, and capacitor C5. The other end of resistor R16 is connected to VCC, the other end of resistor R17 is connected to the PE terminal of the AC terminal block, and the other end of capacitor C5 is connected to the PE terminal of the AC terminal block. Its seventh pin is connected to one end of resistor R18, and one end of capacitor C6 is connected to VCC. The other end of capacitor C6 is connected to the PE terminal of the AC terminal block.

[0024] Optocoupler U3 has its first end connected to the other end of resistor R18, its second end connected to the PE terminal of the AC terminal block, its third end connected to the fourth end of optocoupler U4, its fourth end connected to one end of resistor R19 and the gate of thyristor Q3, the other end of resistor R19 connected to the PE terminal of the AC terminal block, the source of thyristor Q3 connected to the PE terminal of the AC terminal block, and the drain of thyristor Q3 connected to the ON / OFF switch.

[0025] The beneficial effects of this utility model are: by designing an AC sampling and auxiliary transformer voltage comparison shell connected to the live wire protection circuit, when the customer terminal ground wire is connected to the live wire, the protection circuit controls the relay (normally open) to disconnect the connection between the ground and the shell, eliminating the harm to the human body caused by the shell being electrified. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A circuit structure diagram of the first embodiment of the housing-connected live wire protection circuit that uses AC sampling and auxiliary transformer voltage comparison provided by this utility model;

[0028] Figure 2 A circuit structure diagram of a second embodiment of a housing-connected live wire protection circuit that uses AC sampling and auxiliary transformer voltage comparison provided by this utility model;

[0029] Figure 3 The first part of the circuit structure diagram of the third embodiment of the housing connected to the live wire protection circuit by AC sampling and auxiliary transformer voltage comparison provided by this utility model;

[0030] Figure 4 This is a second part of the circuit structure diagram of a third embodiment of a housing-connected live wire protection circuit that uses AC sampling and auxiliary transformer voltage comparison, provided by this utility model. Detailed Implementation

[0031] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0032] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the present invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0033] Please see Figures 1-4 This utility model provides a casing-connected live wire protection circuit that compares AC sampling and auxiliary transformer voltage, comprising:

[0034] Connected to a single-phase AC mains power supply, or a two-phase AC mains power supply with two live wires, or a three-phase AC mains power supply with three live wires, the live wire protection circuit includes:

[0035] AC terminal block, which is connected to the AC single-phase mains power, or AC two-phase dual-wire mains power, or AC three-phase three-wire mains power;

[0036] A bridge rectifier circuit includes four diodes D1, D2, D3 and D4. The common terminal of D1 and D2 is connected to the L terminal or L1 terminal of the AC terminal block. The common terminal of D1 and D3 is grounded. The common terminal of D3 and D4 is connected to the N terminal or L2 terminal of the AC terminal block.

[0037] Crystal oscillator Y1, one end of which is connected to the common terminal of D2 and D4, and the other end of which is connected to the common terminal of D1 and D3;

[0038] Inductor T1A, its first terminal is connected to the common terminal of D2 and D4, its third terminal is connected to the drain of transistor Q1, and the source of transistor Q1 is grounded;

[0039] One end of capacitor CY1 is connected to the common terminal of D1 and D2, and the other end of capacitor CY1 is connected to one end of resistor R1. The other end of resistor R1 is connected to the positive terminal of diode D8 and one end of resistor R3. The other end of resistor R3 is connected to the PE terminal of the AC terminal.

[0040] One end of capacitor CY2 is connected to the common terminal of D3 and D4, and the other end of capacitor CY2 is connected to one end of resistor R2. The other end of resistor R2 is connected to the positive terminal of diode D7 and one end of resistor R4. The other end of resistor R4 is connected to the PE terminal of the AC terminal.

[0041] The negative terminals of diodes D7 and D8 are connected to the AC1 terminal of the contactor. One end of resistor R5 is connected to the AC1 terminal of the contactor, and the other end of resistor R5 is connected to the PE terminal of the AC terminal. One end of capacitor C3 is connected to the AC1 terminal of the contactor, and the other end of capacitor C3 is connected to the PE terminal of the AC terminal.

[0042] One end of resistor R5 is connected to the AC1 terminal of the contactor, and the other end of resistor R5 is connected to the second terminal of comparator ICA. One end of resistor R6 is connected to ACVREF, and the other end of resistor R5 is connected to the third terminal of comparator ICA. The first terminal of comparator ICA is connected to one end of resistor R7, and the other end of resistor R7 is connected to the ON / OFF switch.

[0043] The relay KJ has its first pin connected to the PE terminal of the AC terminal block, its fourth pin connected to the collector of transistor Q2, the base of transistor Q2 connected to the ON / OFF switch, the emitter of transistor Q2 connected to the PE terminal of the AC terminal block, and its fifth pin connected to the housing.

[0044] In a specific embodiment, the protection circuit further includes:

[0045] Inductor T1B has its fourth terminal connected to the positive terminal of diode D5, its third terminal connected to the PE terminal of the AC terminal block, the negative terminal of diode D5 connected to the VCC terminal and to one end of capacitor C1, and the other end of capacitor C1 connected to the PE terminal of the AC terminal block.

[0046] The inductor T1C has its fourth terminal connected to the positive terminal of diode D6, its third terminal connected to the PE terminal of the AC terminal block, the negative terminal of diode D6 connected to the VCC terminal and to one end of capacitor C2, and the other end of capacitor C2 connected to the PE terminal of the AC terminal block.

[0047] In a specific embodiment, when connected to single-phase AC mains power, the L terminal of the AC terminal is connected to the PE terminal of the distribution box, the N terminal of the AC terminal is connected to the N terminal of the distribution box, and the PE terminal of the AC terminal is connected to the L terminal of the distribution box.

[0048] Please refer to the details. Figure 1 When the user has single-phase AC mains power and the ground port is connected to the live wire, the voltage of the remaining two neutral wires and the ground input is essentially zero. The auxiliary power supply is not working, and the protection relay, without power, will remain in the normally open state. The casing and the live wire mistakenly connected to ground are at high impedance, and the casing is not energized. When properly wired, the voltage level at pin 2 of the comparator is lower than that at pin 3 due to the voltage divider resistor design. Pin 1 outputs a high level, controlling the relay to close, and the casing is normally connected to ground.

[0049] In a specific embodiment, when connected to a two-phase dual-live-wire AC mains power supply, the L terminal of the AC terminal is connected to the PE terminal of the distribution box, the N terminal of the AC terminal is connected to the L2 terminal of the distribution box, and the PE terminal of the AC terminal is connected to the L1 terminal of the distribution box.

[0050] Please refer to the details. Figure 2 When the user has a two-phase AC dual-live-wire connection and the ground port is connected to the live wire, the voltage difference between one of the live wires and the input port PE is the voltage difference between the two live wires. This voltage is divided by the AC detection and sent to pin 2 of the comparator TIC. Pin 3 of the IC is the rectified voltage of the transformer winding T1C, which changes with the positive input. T1C is wound in phase with T1A. The voltage ACVREF will change with the input voltage. At this time, the input voltage is one live wire and one ground, which is equivalent to 220V. Pin 3 of the comparator detects 220V, and pin 2 of the comparator detects 380V. The voltage at pin 3 is higher than the voltage at pin 2, so the comparator outputs a low level. The relay does not work and remains in the normally open state. The casing and the live wire that is mistakenly connected to ground are in a high impedance state, and the casing is not energized.

[0051] When the wiring is normal, the comparator's pin 3 ACVREF is at a high level because of the dual live wire input, while the comparator's pin 2 is at a low level because of the voltage division between the live wire and PE. The level at pin 2 is lower than the level at pin 3, so pin 1 outputs a high level, controlling the relay to close, and the casing is normally connected to ground.

[0052] In a specific embodiment, when connected to a three-phase three-wire AC mains power supply, the L1 terminal of the AC terminal is connected to the L1 terminal of the distribution box, the L2 terminal of the AC terminal is connected to the L2 terminal of the distribution box, and the PE terminal of the AC terminal is connected to the L3 terminal of the distribution box.

[0053] Comparator U2B has its 5th pin connected to the common terminal of resistors R8 and R9. The other end of resistor R8 is connected to the PE terminal of the AC terminal block, and the other end of resistor R9 is connected to ACVREF. Its 6th pin is connected to the common terminal of resistors R10, R11, and capacitor C4. The other end of resistor R10 is connected to VCC, the other end of resistor R11 is connected to the PE terminal of the AC terminal block, and the other end of capacitor C4 is connected to the PE terminal of the AC terminal block. Its 7th pin is connected to one end of resistor R12.

[0054] Optocoupler U4 has its first end connected to the other end of resistor R12, its second end connected to the PE terminal of the AC terminal block, and its third end connected to one end of R13, with the other end of R13 connected to VCC.

[0055] Comparator U2C has its third pin connected to the common terminal of resistors R14 and R15. The other end of resistor R14 is connected to the PE terminal of the AC terminal block, and the other end of resistor R15 is connected to AC1. Its second pin is connected to the common terminal of resistors R16, R17, and capacitor C5. The other end of resistor R16 is connected to VCC, the other end of resistor R17 is connected to the PE terminal of the AC terminal block, and the other end of capacitor C5 is connected to the PE terminal of the AC terminal block. Its seventh pin is connected to one end of resistor R18, and one end of capacitor C6 is connected to VCC. The other end of capacitor C6 is connected to the PE terminal of the AC terminal block.

[0056] Optocoupler U3 has its first end connected to the other end of resistor R18, its second end connected to the PE terminal of the AC terminal block, its third end connected to the fourth end of optocoupler U4, its fourth end connected to one end of resistor R19 and the gate of thyristor Q3, the other end of resistor R19 connected to the PE terminal of the AC terminal block, the source of thyristor Q3 connected to the PE terminal of the AC terminal block, and the drain of thyristor Q3 connected to the ON / OFF switch.

[0057] Please refer to the details. Figures 3-4When the customer connects the AC terminal to the three live wires, the PE port is connected to the live wire. The voltage at pin 3 (AC1) of U2A is higher than that at pin 2, and pin 1 of U2A is at a high level, causing optocoupler U3 to conduct. At the same time, because the input is a dual live wire, T1C is wound in phase with T1A, and the rectified voltage ACVREF of T1C is at a high level. The voltage at pin 5 of U2B is higher than that at pin 6, causing optocoupler U4 to conduct. At this time, U3 and U4 conduct simultaneously, the gate pin of Q3 is at a high level, Q3 conducts, the ON / OFF is pulled low, the relay does not work and remains in the normally open state, the casing and the live wire mistakenly connected to ground are at high impedance, and the casing is not energized.

[0058] When properly wired, the voltage of AC1 is a low level due to the voltage divider between the live wire and PE. The voltage level at pin 3 of U2A is lower than that at pin 2, and the output voltage at pin 1 of U2A is high. Optocoupler U3 is not conducting, and Q3 is not conducting. Since AC1 is low, ACERF is high when there are two live wire inputs. Therefore, the voltage level at pin 3 of ICA is higher than that at pin 2, and the output voltage at pin 1 of ICA is high. The relay is conducting, and the casing is normally connected to ground.

[0059] The beneficial effects of this utility model are: by designing an AC sampling and auxiliary transformer voltage comparison shell connected to the live wire protection circuit, when the customer terminal ground wire is connected to the live wire, the protection circuit controls the relay (normally open) to disconnect the connection between the ground and the shell, eliminating the harm to the human body caused by the shell being electrified.

[0060] The above are merely preferred embodiments of this utility model, but the scope of protection of this utility model is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the scope of protection of this utility model.

Claims

1. A casing connected to a live wire protection circuit via AC sampling and auxiliary transformer voltage comparison, connected to a single-phase AC mains power supply, or a two-phase AC mains power supply with two live wires, or a three-phase AC mains power supply with three live wires, characterized in that... The fire protection circuit includes: AC terminal block, which is connected to the AC single-phase mains power, or AC two-phase dual-wire mains power, or AC three-phase three-wire mains power; A bridge rectifier circuit includes four diodes D1, D2, D3 and D4. The common terminal of D1 and D2 is connected to the L terminal or L1 terminal of the AC terminal block. The common terminal of D1 and D3 is grounded. The common terminal of D3 and D4 is connected to the N terminal or L2 terminal of the AC terminal block. Crystal oscillator Y1, one end of which is connected to the common terminal of D2 and D4, and the other end of which is connected to the common terminal of D1 and D3; Inductor T1A, its first terminal is connected to the common terminal of D2 and D4, its third terminal is connected to the drain of transistor Q1, and the source of transistor Q1 is grounded; One end of capacitor CY1 is connected to the common terminal of D1 and D2, and the other end of capacitor CY1 is connected to one end of resistor R1. The other end of resistor R1 is connected to the positive terminal of diode D8 and one end of resistor R3. The other end of resistor R3 is connected to the PE terminal of the AC terminal. One end of capacitor CY2 is connected to the common terminal of D3 and D4, and the other end of capacitor CY2 is connected to one end of resistor R2. The other end of resistor R2 is connected to the positive terminal of diode D7 and one end of resistor R4. The other end of resistor R4 is connected to the PE terminal of the AC terminal. The negative terminals of diodes D7 and D8 are connected to the AC1 terminal of the contactor. One end of resistor R5 is connected to the AC1 terminal of the contactor, and the other end of resistor R5 is connected to the PE terminal of the AC terminal. One end of capacitor C3 is connected to the AC1 terminal of the contactor, and the other end of capacitor C3 is connected to the PE terminal of the AC terminal. One end of resistor R5 is connected to the AC1 terminal of the contactor, and the other end of resistor R5 is connected to the second terminal of comparator ICA. One end of resistor R6 is connected to ACVREF, and the other end of resistor R5 is connected to the third terminal of comparator ICA. The first terminal of comparator ICA is connected to one end of resistor R7, and the other end of resistor R7 is connected to the ON / OFF switch. The relay KJ has its first pin connected to the PE terminal of the AC terminal block, its fourth pin connected to the collector of transistor Q2, the base of transistor Q2 connected to the ON / OFF switch, the emitter of transistor Q2 connected to the PE terminal of the AC terminal block, and its fifth pin connected to the housing.

2. The casing-connected live wire protection circuit according to claim 1, which compares AC sampling and auxiliary transformer voltage, is characterized in that... Also includes: Inductor T1B has its fourth terminal connected to the positive terminal of diode D5, its third terminal connected to the PE terminal of the AC terminal block, the negative terminal of diode D5 connected to the VCC terminal and to one end of capacitor C1, and the other end of capacitor C1 connected to the PE terminal of the AC terminal block.

3. The casing-connected live wire protection circuit according to claim 1, which compares AC sampling and auxiliary transformer voltage, is characterized in that... Also includes: The inductor T1C has its fourth terminal connected to the positive terminal of diode D6, its third terminal connected to the PE terminal of the AC terminal block, the negative terminal of diode D6 connected to the VCC terminal and to one end of capacitor C2, and the other end of capacitor C2 connected to the PE terminal of the AC terminal block.

4. The casing-connected live wire protection circuit according to any one of claims 1-3, characterized in that: When connected to single-phase AC mains power, the L terminal of the AC terminal is connected to the PE terminal of the distribution box, the N terminal of the AC terminal is connected to the N terminal of the distribution box, and the PE terminal of the AC terminal is connected to the L terminal of the distribution box.

5. The casing-connected live wire protection circuit according to any one of claims 1-3, characterized in that: When connected to a two-phase dual-live-wire AC mains power supply, the L terminal of the AC terminal is connected to the PE terminal of the distribution box, the N terminal of the AC terminal is connected to the L2 terminal of the distribution box, and the PE terminal of the AC terminal is connected to the L1 terminal of the distribution box.

6. The casing-connected live wire protection circuit according to any one of claims 1-3, characterized in that: When connected to a three-phase, three-wire AC mains power supply, the L1 terminal of the AC terminal is connected to the L1 terminal of the distribution box, the L2 terminal of the AC terminal is connected to the L2 terminal of the distribution box, and the PE terminal of the AC terminal is connected to the L3 terminal of the distribution box.

7. The casing-connected live wire protection circuit according to claim 6, which compares AC sampling and auxiliary transformer voltage, is characterized in that... Also includes: Comparator U2B has its 5th pin connected to the common terminal of resistors R8 and R9. The other end of resistor R8 is connected to the PE terminal of the AC terminal block, and the other end of resistor R9 is connected to ACVREF. Its 6th pin is connected to the common terminal of resistors R10, R11, and capacitor C4. The other end of resistor R10 is connected to VCC, the other end of resistor R11 is connected to the PE terminal of the AC terminal block, and the other end of capacitor C4 is connected to the PE terminal of the AC terminal block. Its 7th pin is connected to one end of resistor R12. Optocoupler U4 has its first end connected to the other end of resistor R12, its second end connected to the PE terminal of the AC terminal block, and its third end connected to one end of R13, with the other end of R13 connected to VCC. Comparator U2C has its third pin connected to the common terminal of resistors R14 and R15. The other end of resistor R14 is connected to the PE terminal of the AC terminal block, and the other end of resistor R15 is connected to AC1. Its second pin is connected to the common terminal of resistors R16, R17, and capacitor C5. The other end of resistor R16 is connected to VCC, the other end of resistor R17 is connected to the PE terminal of the AC terminal block, and the other end of capacitor C5 is connected to the PE terminal of the AC terminal block. Its seventh pin is connected to one end of resistor R18, and one end of capacitor C6 is connected to VCC. The other end of capacitor C6 is connected to the PE terminal of the AC terminal block. Optocoupler U3 has its first end connected to the other end of resistor R18, its second end connected to the PE terminal of the AC terminal block, its third end connected to the fourth end of optocoupler U4, its fourth end connected to one end of resistor R19 and the gate of thyristor Q3, the other end of resistor R19 connected to the PE terminal of the AC terminal block, the source of thyristor Q3 connected to the PE terminal of the AC terminal block, and the drain of thyristor Q3 connected to the ON / OFF switch.

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