Power loss alarm device for three-phase alternating current power supply

Abstract

The utility model discloses a three-phase alternating current power supply power-loss alarm device, belongs to the technical field of circuits, and solves the problems that the existing SVG indoor power supply alarm device uses a controller to directly detect the safety risk of a circuit and the driving voltage of an alarm is high. Comprising an isolation circuit, a main control circuit, an LED drive circuit and a buzzing drive circuit, and the main control circuit is connected with the isolation circuit, the LED drive circuit and the buzzing drive circuit; the control mode that the optocoupler drives the field effect transistor is adopted, isolation of strong current and weak current and switching-on and switching-off of the main control circuit are achieved, the circuit structure is made to be simple, used components are reduced, and system power consumption and design cost are effectively reduced; meanwhile, high working voltage is provided for the piezoelectric buzzer through the boost inductor, the input cost is reduced, the working voltage of the device is reduced, and the safety and reliability of the alarm device are improved.

Description

Technical Field

[0001] This utility model belongs to the field of circuit technology and relates to a three-phase AC power failure alarm device. Background Technology

[0002] Static var generators (SVG) are used to provide reactive power compensation to help stabilize the voltage of the power grid. SVG compensation devices reduce voltage fluctuations in the power system by dynamically adjusting reactive power, thereby improving the stability and efficiency of the power system.

[0003] The existing SVG is installed indoors, with a fully enclosed internal circulation cooling system to dissipate and cool the heat generated by the SVG's IGBTs during operation. To ensure the safe and reliable operation of the SVG equipment and prevent overheating and tripping due to power failure of the indoor air conditioning, it is crucial to design a power failure alarm device for the SVG's cooling and air conditioning power supply. When the three-phase AC power supply to the cooling and air conditioning system fails, the alarm device should emit audible and flashing signals to alert substation personnel to promptly investigate the fault and prevent excessively high indoor temperatures from causing the SVG to trip due to insufficient heat dissipation.

[0004] In reality, since three-phase AC power is 380V, which is not a safe voltage, directly detecting the circuit using a controller poses a safety risk and makes it difficult to guarantee the safety of personnel operation and equipment operation. Secondly, when conventional alarm devices use piezoelectric buzzers as electroacoustic transducers, a high-decibel alarm sound source is often required, which cannot be met when the alarm device is powered by a battery. Utility Model Content

[0005] The technical solution of this utility model is used to solve the problems of safety risks and high alarm drive voltage in existing SVG indoor power alarm devices that use controllers to directly detect circuits.

[0006] This utility model solves the above-mentioned technical problems through the following technical solution:

[0007] A three-phase AC power failure alarm device includes an isolation circuit, a main control circuit, an LED driver circuit, and a buzzer driver circuit; the main control circuit is connected to the isolation circuit, the LED driver circuit, and the buzzer driver circuit respectively.

[0008] The main control circuit includes a main control chip U1, a battery BT1, a potentiometer RP1 with a switch, a field-effect transistor Q1, a diode D3, a resistor R3, a resistor R4, and a capacitor C3; the main control chip 1 #The pin is connected to one end of resistor R4, and the other end of resistor R4 is connected to the power supply. Capacitor C3 is connected in parallel with diode D3, and the cutoff terminal of diode D3 is connected to the main control chip's pin 1. # Pin 1: The conducting terminal of diode D3 is connected to the drain of MOSFET Q1. One end of resistor R3 is connected to the gate of MOSFET Q1, and the other end of resistor R3 is connected to the source of MOSFET Q1. The source of MOSFET Q1 is connected to the negative terminal of battery BT1. The positive terminal of battery BT1 is connected to the output terminal of potentiometer RP1 with a switch. The sliding terminal of potentiometer RP1 with a switch is connected to the buzzer drive circuit. The input terminal of potentiometer RP1 with a switch is connected to the power supply. Pin 2: The main control chip has 6 pins. # The pins are connected to the LED driver circuit, and the main control chip's 8 # The pins are connected to the buzzer driver circuit, and the main control chip's 8 # Pin grounded;

[0009] The isolation circuit includes optocouplers J1 and J2, a varistor R0, diodes D1 and D2, resistors R1 and R2, and capacitors C1 and C2. The conducting terminals of diodes D1 and D2, and one end of the varistor R0, are respectively connected to the three transmission lines of the three-phase AC power supply. The cut-off terminal of diode D1 is connected to one end of resistor R1, and the other end of resistor R1 is connected to the first input terminal of optocoupler J1. The cut-off terminal of diode D2 is connected to one end of resistor R2, and the other end of resistor R2 is connected to the first input terminal of optocoupler J2. The other end of the varistor R0 is connected to the optocoupler... The second input terminal of optocoupler J1 and the second input terminal of optocoupler J2 are connected; one end of capacitor C1 is connected to the cutoff terminal of diode D1, and the other end of capacitor C1 is connected between varistor R0 and optocoupler J2; one end of capacitor C2 is connected to the cutoff terminal of diode D2, and the other end of capacitor C2 is connected between varistor R0 and optocoupler J2; the first output terminal of optocoupler J1 is connected to the gate of field-effect transistor Q1; the second output terminal of optocoupler J1 is connected to the first output terminal of optocoupler J2; the second output terminal of optocoupler J2 is connected to the negative terminal of battery BT1; and the second output terminal of optocoupler J2 is grounded.

[0010] Furthermore, the potentiometer RP1 with switch is model WH149, with a maximum resistance of 500KΩ.

[0011] Furthermore, the optocoupler J1 and optocoupler J2 are model F222817C.

[0012] Furthermore, the main control chip U1 is a PIC12C508A.

[0013] Furthermore, the field-effect transistor Q1 is an N-channel field-effect transistor of model K4145.

[0014] Furthermore, the battery BT1 is a 9V alkaline battery.

[0015] Further, the LED driving circuit includes LED1, LED2, LED3, LED4, transistor Q2, and resistor R5. LED1 and LED2 are connected in series, and LED3 and LED4 are connected in series. The conducting terminals of LED1 and LED3 are connected together and then connected to the negative terminal of battery BT1. Both the conducting terminals of LED1 and LED3 are connected to the power supply. The cutoff terminals of LED2 and LED4 are connected together and then connected to the collector of transistor Q2. The emitter of transistor Q2 is grounded. The base of transistor Q2 is connected to one end of resistor R5, and the other end of resistor R5 is connected to pin 6 of the main control chip U1. # Pin connection.

[0016] Furthermore, the buzzer drive circuit includes a buzzer J3, a boost inductor L1, a transistor Q3, and a resistor R6. One end of the buzzer J3 is connected to the sliding terminal of a potentiometer RP1 with a switch, and the other end of the buzzer J3 is connected to the output terminal of the boost inductor L1. The input terminal of the boost inductor L1 is connected to a power supply. The control terminal of the boost inductor L1 is connected to the collector of the transistor Q3. The emitter of the transistor Q3 is grounded. The base of the transistor Q3 is connected to one end of the resistor R6, and the other end of the resistor R6 is connected to the 5-pin connector of the main control chip U1. # Pin connection.

[0017] Furthermore, the boost inductor L1 is model PK3W0912 with an inductance value of 76mH.

[0018] The advantages of this utility model are:

[0019] (1) This utility model converts 380V three-phase sinusoidal AC power into DC power that can drive the input of the optocoupler through the isolation circuit after rectification and step-down, and uses it as the input of the optocoupler signal control; at the same time, the optocoupler is used to isolate the high voltage and low voltage parts in the alarm device, effectively ensuring the safety of personnel operation and the safety of device operation.

[0020] (2) This utility model uses a three-legged boost inductor to boost the driving power supply voltage through a buzzer drive circuit. Based on the working principle of electromagnetic induction and magnetic field transmission of inductors, the switch in the buzzer drive circuit is controlled by the control circuit to adjust the charging and discharging cycle of the boost inductor to obtain higher driving power. A charge accumulation and release process is formed in the buzzer drive circuit, thereby boosting the input voltage to the working voltage required by the buzzer and increasing the alarm volume of the buzzer. Even with a 9V power supply battery, a high decibel alarm sound can be achieved.

[0021] (3) This utility model adopts the control method of optocoupler driving field effect transistor to realize the isolation between strong and weak currents and the opening and closing of the main control circuit, which makes the circuit structure simple, reduces the number of components used, and effectively reduces system power consumption and design cost; at the same time, it provides high working voltage to the piezoelectric buzzer through the boost inductor, which reduces investment costs and lowers the working voltage of the device, thereby improving the safety and reliability of the alarm device. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a three-phase AC power failure alarm device according to Embodiment 1 of this utility model;

[0023] Figure 2 This is a schematic diagram of the isolation circuit according to Embodiment 1 of this utility model;

[0024] Figure 3 This is a schematic diagram of the LED driving circuit and the buzzer driving circuit of Embodiment 1 of this utility model;

[0025] Figure 4 This is a schematic diagram of the main control circuit of Embodiment 1 of this utility model. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below in conjunction with the embodiments of this utility model. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0027] The technical solution of this utility model will be further described below with reference to the accompanying drawings and specific embodiments:

[0028] Example 1

[0029] like Figure 1As shown, specifically, a three-phase AC power failure alarm device is disclosed, including an isolation circuit, a main control circuit, an LED driving circuit, and a buzzer driving circuit; the main control circuit is connected to the isolation circuit, the LED driving circuit, and the buzzer driving circuit respectively.

[0030] The main control circuit includes a main control chip U1, a battery BT1, a potentiometer RP1 with a switch, a field-effect transistor Q1, a diode D3, a resistor R3, a resistor R4, and a capacitor C3; the main control chip 1 # The pin is connected to one end of resistor R4, and the other end of resistor R4 is connected to the power supply. Capacitor C3 is connected in parallel with diode D3, and the cutoff terminal of diode D3 is connected to the main control chip's pin 1. # Pin 1: The conducting terminal of diode D3 is connected to the drain of MOSFET Q1. One end of resistor R3 is connected to the gate of MOSFET Q1, and the other end of resistor R3 is connected to the source of MOSFET Q1. The source of MOSFET Q1 is connected to the negative terminal of battery BT1. The positive terminal of battery BT1 is connected to the output terminal of potentiometer RP1 with a switch. The sliding terminal of potentiometer RP1 with a switch is connected to the buzzer drive circuit. The input terminal of potentiometer RP1 with a switch is connected to the power supply. Pin 2: The main control chip has 6 pins. # The pins are connected to the LED driver circuit, and the main control chip's 8 # The pins are connected to the buzzer driver circuit, and the main control chip's 8 # The pin is grounded.

[0031] Furthermore, the power supply voltage is 9V.

[0032] Furthermore, the resistor R3 has a resistance of 3MΩ, the resistor R4 has a resistance of 1KΩ, the diode D3 has a forward voltage of 5.1V, and the potentiometer RP1 with switch is model WH149 with a maximum resistance of 500KΩ.

[0033] Specifically, the battery BT1 is a 9V alkaline battery; the field-effect transistor Q1 is a K4145 N-channel field-effect transistor; and the main control chip U1 is a PIC12C508A.

[0034] In this embodiment, the main control circuit uses a transistor amplifier circuit to increase the load drive current of the active chip U1, ensuring that the output of the active chip U1 is stable and reliable. At the same time, the use of only an 8-pin microcontroller can reduce design costs and resource requirements.

[0035] The isolation circuit includes optocouplers J1 and J2, a varistor R0, diodes D1 and D2, resistors R1 and R2, and capacitors C1 and C2. The conducting terminals of diodes D1 and D2, and one end of the varistor R0, are respectively connected to the three transmission lines of the three-phase AC power supply. The cut-off terminal of diode D1 is connected to one end of resistor R1, and the other end of resistor R1 is connected to the first input terminal of optocoupler J1. The cut-off terminal of diode D2 is connected to one end of resistor R2, and the other end of resistor R2 is connected to the first input terminal of optocoupler J2. The other end of the varistor R0 is connected to the optocoupler... The second input terminal of optocoupler J1 and the second input terminal of optocoupler J2 are connected; one end of capacitor C1 is connected to the cutoff terminal of diode D1, and the other end of capacitor C1 is connected between varistor R0 and optocoupler J2; one end of capacitor C2 is connected to the cutoff terminal of diode D2, and the other end of capacitor C2 is connected between varistor R0 and optocoupler J2; the first output terminal of optocoupler J1 is connected to the gate of field-effect transistor Q1; the second output terminal of optocoupler J1 is connected to the first output terminal of optocoupler J2; the second output terminal of optocoupler J2 is connected to the negative terminal of battery BT1; and the second output terminal of optocoupler J2 is grounded.

[0036] Furthermore, the resistance of resistors R1 and R2 is 1MΩ, the capacitance of capacitors C1 and C2 is 15nF, and the maximum voltage they can withstand is 630V.

[0037] Specifically, diodes D1 and D2 are of model number IN4007, and optocouplers J1 and J2 are of model number F222817C.

[0038] Specifically, the varistor R0 is a metal oxide varistor with a resistance of 471KΩ. In this embodiment, the varistor is used to protect electrical equipment from damage caused by high voltage surges. It has a high resistance under normal operating voltage and does not affect the operation of the normal circuit. When the isolation circuit encounters excessively high voltage, the resistance of the varistor drops rapidly, forming a low-resistance state, shorting the excessively high voltage to the ground wire, and protecting other circuit components in the circuit.

[0039] In this embodiment, the isolation circuit is used to convert the 380V three-phase sinusoidal AC power into a DC power supply that can drive the input of the optocoupler after rectification and step-down by diodes D1 and D2, and is used as the optocoupler signal control input; at the same time, the optocoupler is used to isolate the high voltage and low voltage parts in the alarm device to ensure the safety of personnel operation and the safe operation of the device.

[0040] In this embodiment, by connecting the three-phase transmission lines of the three-phase AC power supply to the high-voltage section of the isolation circuit, when the three-phase AC power supply is energized, the sampling signal is input to the isolation circuit. The high-voltage section of the isolation circuit rectifies, filters, and reduces the voltage of the input sampling signal before inputting it to the optocoupler. The output of the optocoupler forces the voltage level of the field-effect transistor Q1 to a low level on the power supply ground, causing the field-effect transistor Q1 to... When the gate-source voltage of MOSFET Q1 is 0, the turn-on threshold voltage of MOSFET Q1 is 0, causing the MOSFET to not work, and the main control circuit cannot work due to lack of power. When the three-phase AC power supply fails, there is no sampling signal at the input of the isolation circuit, the output of the optocoupler is open, the gate of MOSFET Q1 is powered by a 9V battery, and is strongly pulled to a high level by the pull-up bias resistor R3, making the gate-source voltage of the MOSFET greater than the turn-on threshold voltage. The drain-source of the MOSFET is saturated and conducts, allowing the main control circuit to work normally after the power supply is turned on. The main control chip U1 controls the LED driver circuit and the buzzer driver circuit to work, and the device emits an audible and visual alarm.

[0041] Before using the alarm device, manually disconnect the air switch of the three-phase AC power supply. By rotating the potentiometer RP1, the four LEDs of the LED driver circuit will flash brightly. At this time, the piezoelectric buzzer J3 of the buzzer driver circuit will emit a soft alarm sound. Continue to turn the potentiometer RP1 to further reduce the effective resistance of the potentiometer. The sound of the buzzer J3 will gradually increase as the potentiometer RP1 is adjusted. Stop rotating when the appropriate sound level is reached. Finally, turn on the air switch of the three-phase AC power supply for the air conditioner. After the three-phase AC power is turned on, both the audible and visual alarms will stop working, completing the test. When a power failure occurs in the three-phase AC power supply, the device will emit an audible and visual alarm.

[0042] The LED driving circuit includes LED1, LED2, LED3, LED4, transistor Q2, and resistor R5. LED1 and LED2 are connected in series, and LED3 and LED4 are connected in series. The conducting terminals of LED1 and LED3 are connected together and then connected to the negative terminal of battery BT1. Both the conducting terminals of LED1 and LED3 are connected to the power supply. The cutoff terminals of LED2 and LED4 are connected together and then connected to the collector of transistor Q2. The emitter of transistor Q2 is grounded. The base of transistor Q2 is connected to one end of resistor R5, and the other end of resistor R5 is connected to pin 6 of the main control chip U1. # Pin connection.

[0043] Specifically, the transistor Q2 is an NPN transistor, model MMBT3904, the resistor R5 has a resistance of 4.7KΩ, and LED1, LED2, LED3, and LED4 are all red LEDs.

[0044] The buzzer drive circuit includes a buzzer J3, a boost inductor L1, a transistor Q3, and a resistor R6. One end of the buzzer J3 is connected to the sliding terminal of a potentiometer RP1 with a switch, and the other end of the buzzer J3 is connected to the output terminal of the boost inductor L1. The input terminal of the boost inductor L1 is connected to the power supply. The control terminal of the boost inductor L1 is connected to the collector of the transistor Q3, the emitter of the transistor Q3 is grounded, the base of the transistor Q3 is connected to one end of the resistor R6, and the other end of the resistor R6 is connected to the 5-pin connector of the main control chip U1. # Pin connection.

[0045] Specifically, the transistor Q2 is an NPN transistor, model MMBT3904, the resistor R6 has a resistance of 1KΩ, and the buzzer J3 is model BEEP-NS.

[0046] Specifically, the boost inductor L1 is model PK3W0912 with an inductance value of 76mH. In this embodiment, utilizing the characteristic of an inductor to store energy and generate a magnetic field in a circuit, when transistor Q3 is turned on, current flows through the boost inductor L1, the inductor stores energy, the magnetic field of the inductor begins to decay, and the inductor attempts to maintain the flow of current, thereby generating a voltage higher than the input voltage across the inductor, forming inductive feedback. The generated high voltage is input to the buzzer J3. At the same time, the main control chip U1 controls transistor Q3 to continuously turn on and off, adjusting the charging and discharging cycle of the inductor, so that the boost inductor L1 continuously charges and releases energy, thereby maintaining the boost state at the output end and inputting the generated high voltage to the buzzer J3.

[0047] In this embodiment, the buzzer drive circuit uses a three-legged boost inductor to boost the drive power supply voltage. The main control chip U1 controls the transistor Q3 to continuously open and close, adjusting the charging and discharging cycle of the inductor to obtain higher drive power and increase the alarm volume. Even with a 9V power supply battery, a high-decibel alarm sound can be achieved.

[0048] Working principle:

[0049] By connecting the three-phase AC power supply lines to the high-voltage section of the isolation circuit, when the three-phase AC power is on, the sampling signal is input to the isolation circuit. The high-voltage section of the isolation circuit rectifies, filters, and reduces the voltage of the input sampling signal before inputting it to the optocoupler. The output of the optocoupler forces the level of the field-effect transistor Q1 to a low level of the power supply ground, making the voltage between the gate and source of the field-effect transistor Q1 zero. The threshold voltage of the field-effect transistor Q1 is zero, causing the field-effect transistor to not work, and the main control circuit cannot work due to the lack of power. When the three-phase AC power is lost, there is no sampling signal at the input of the isolation circuit, the output of the optocoupler is open, and the gate of the field-effect transistor Q1 is powered by a 9V battery. It is pulled to a high level by the pull-up bias resistor R3, making the voltage between the gate and source of the MOSFET greater than the threshold voltage. The drain and source of the MOSFET saturates and conducts, allowing the main control circuit to work normally after the power supply is turned on. The main control chip U1 controls the LED driver circuit and the buzzer driver circuit to work, and the device emits an audible and visual alarm.

[0050] Before using the alarm device, manually disconnect the air switch of the three-phase AC power supply. By rotating the potentiometer RP1, the four LEDs of the LED driver circuit will flash brightly. At this time, the piezoelectric buzzer J3 of the buzzer driver circuit will emit a soft alarm sound. Continue to turn the potentiometer RP1 to further reduce the effective resistance of the potentiometer. The sound of the buzzer J3 will gradually increase as the potentiometer RP1 is adjusted. Stop rotating when the appropriate sound level is reached. Finally, turn on the air switch of the three-phase AC power supply for the air conditioner. After the three-phase AC power is turned on, both the audible and visual alarms will stop working, completing the test. When a power failure occurs in the three-phase AC power supply, the device will emit an audible and visual alarm.

[0051] The above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A three-phase AC power failure alarm device, characterized in that, It includes an isolation circuit, a main control circuit, an LED driver circuit, and a buzzer driver circuit; the main control circuit is connected to the isolation circuit, the LED driver circuit, and the buzzer driver circuit respectively. The main control circuit includes a main control chip U1, a battery BT1, a potentiometer RP1 with a switch, a field-effect transistor Q1, a diode D3, a resistor R3, a resistor R4, and a capacitor C3; the main control chip 1 # The pin is connected to one end of resistor R4, and the other end of resistor R4 is connected to the power supply. Capacitor C3 is connected in parallel with diode D3, and the cutoff terminal of diode D3 is connected to the main control chip's pin 1. # Pin 1: The conducting terminal of diode D3 is connected to the drain of MOSFET Q1. One end of resistor R3 is connected to the gate of MOSFET Q1, and the other end of resistor R3 is connected to the source of MOSFET Q1. The source of MOSFET Q1 is connected to the negative terminal of battery BT1. The positive terminal of battery BT1 is connected to the output terminal of potentiometer RP1 with a switch. The sliding terminal of potentiometer RP1 with a switch is connected to the buzzer drive circuit. The input terminal of potentiometer RP1 with a switch is connected to the power supply. Pin 2: The main control chip has 6 pins. # The pins are connected to the LED driver circuit, and the main control chip's 8 # The pins are connected to the buzzer driver circuit, and the main control chip's 8 # Pin grounded; The isolation circuit includes optocouplers J1 and J2, a varistor R0, diodes D1 and D2, resistors R1 and R2, and capacitors C1 and C2. The conducting terminals of diodes D1 and D2, and one end of the varistor R0, are respectively connected to the three transmission lines of the three-phase AC power supply. The cut-off terminal of diode D1 is connected to one end of resistor R1, and the other end of resistor R1 is connected to the first input terminal of optocoupler J1. The cut-off terminal of diode D2 is connected to one end of resistor R2, and the other end of resistor R2 is connected to the first input terminal of optocoupler J2. The other end of the varistor R0 is connected to the optocoupler... The second input terminal of optocoupler J1 and the second input terminal of optocoupler J2 are connected; one end of capacitor C1 is connected to the cutoff terminal of diode D1, and the other end of capacitor C1 is connected between varistor R0 and optocoupler J2; one end of capacitor C2 is connected to the cutoff terminal of diode D2, and the other end of capacitor C2 is connected between varistor R0 and optocoupler J2; the first output terminal of optocoupler J1 is connected to the gate of field-effect transistor Q1; the second output terminal of optocoupler J1 is connected to the first output terminal of optocoupler J2; the second output terminal of optocoupler J2 is connected to the negative terminal of battery BT1; and the second output terminal of optocoupler J2 is grounded.

2. The three-phase AC power failure alarm device according to claim 1, characterized in that, The potentiometer RP1 with switch is model WH149, with a maximum resistance of 500KΩ.

3. The three-phase AC power failure alarm device according to claim 1, characterized in that, The optocouplers J1 and J2 are model F222817C.

4. A three-phase AC power failure alarm device according to claim 1, characterized in that, The main control chip U1 is a PIC12C508A.

5. A three-phase AC power failure alarm device according to claim 1, characterized in that, The field-effect transistor Q1 is an N-channel field-effect transistor of model K4145.

6. A three-phase AC power failure alarm device according to claim 1, characterized in that, The battery BT1 is a 9V alkaline battery.

7. A three-phase AC power failure alarm device according to claim 1, characterized in that, The LED driving circuit includes LED1, LED2, LED3, LED4, transistor Q2, and resistor R5. LED1 and LED2 are connected in series, and LED3 and LED4 are connected in series. The conducting terminals of LED1 and LED3 are connected together and then connected to the negative terminal of battery BT1. Both the conducting terminals of LED1 and LED3 are connected to the power supply. The cutoff terminals of LED2 and LED4 are connected together and then connected to the collector of transistor Q2. The emitter of transistor Q2 is grounded. The base of transistor Q2 is connected to one end of resistor R5, and the other end of resistor R5 is connected to pin 6 of the main control chip U1. # Pin connection.

8. A three-phase AC power failure alarm device according to claim 1, characterized in that, The buzzer drive circuit includes a buzzer J3, a boost inductor L1, a transistor Q3, and a resistor R6. One end of the buzzer J3 is connected to the sliding terminal of a potentiometer RP1 with a switch, and the other end of the buzzer J3 is connected to the output terminal of the boost inductor L1. The input terminal of the boost inductor L1 is connected to the power supply. The control terminal of the boost inductor L1 is connected to the collector of the transistor Q3, the emitter of the transistor Q3 is grounded, the base of the transistor Q3 is connected to one end of the resistor R6, and the other end of the resistor R6 is connected to the 5-pin connector of the main control chip U1. # Pin connection.

9. A three-phase AC power failure alarm device according to claim 8, characterized in that, The boost inductor L1 is model PK3W0912 with an inductance value of 76mH.

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