Mains voltage two-way over-limit alarm protector circuit

Mains voltage two-way over-limit alarm protector This alarm protector can sound and light alarm when the mains voltage is higher or lower than the specified value, and at the same time automatically cut off the power supply of electrical appliances to protect the electrical appliances from damage. The device is small in size, fully functional, simple to make and highly practical. Working principle 　　　　　 　　: The mains voltage is stepped down by C3, stabilized by DW, and rectified and filtered by VD6, VD7, and C2 to output a 12V stable DC voltage supply circuit. The other route is VD1 rectifier, R1 step-down, C1 filter, and generates about 10.5V voltage on RP1 and RP2 to detect the mains voltage change input signal. Gates IC1A and IC1B form an overvoltage detection circuit, IC1C is an undervoltage detection circuit, IC1D is a switch, and IC1E, IC1F and piezoelectric ceramic sheet YD form an audio pulse oscillator. Transistor VT and relay J form a protective action circuit. The red LED1 is used as a mains overvoltage indication, and the green tube LED2 is used as a mains undervoltage indication. When the mains power is normal, non-IC1A outputs high level, IC1B and IC1C output low level, LED1 and LED2 are cut off and do not emit light, VT is cut off, J does not operate, the appliance is powered normally, at this time point B is high level, F4 output Low level, VD5 is turned on, point C is low level, the audio pulse oscillator stops vibrating, and YD does not sound. When the mains power is over-voltage or under-voltage, one of IC1B and IC1C outputs a high level, causing point A to become a high potential, VT is saturated and turned on, J is energized and closed, and the electrical power is disconnected. At this time, point B becomes Low potential, IC1D outputs high level, VD5 is cut off, the reverse resistance is very large, which is equivalent to an open circuit, the audio pulse oscillator starts to oscillate, YD emits an alarm sound, and the corresponding light-emitting diode emits light at the same time. The component selection and production component list is shown in the table below. No. Name Model Quantity R1 Resistor 470K/1W 1 R2, R3, R4 Resistor 2K 3 R5 Resistor 100K 1 R6 Metal film resistor 1M/1W 1 RP1, RP2 Trimming resistor 100K 2 C1 Electrolytic capacitor 100u/16V 1 C2 Electrolytic capacitor 220u/16V 1 C3 metallized paper capacitor 1u/400V 1 C4 polyester capacitor 1800 1 VD1, VD4, VD6, VD7 rectifier diode IN4007 4 VD2, VD3, VD5 switching diode IN4148 3 VDW Zener diode 12V/1W 1 LED1, LED2 light emitting diode red , 1 each green 2 VT1 transistor 9013 1 IC1 Six-NOT gate integrated circuit CD4069 or C033 1 YD Piezoelectric ceramic piece plus sound cavity 1 CZ AC socket 1 J Electromagnetic relay coil voltage 12V, contact current selected as needed 1 During debugging , use a voltage regulator to supply power, adjust the voltage to the normal value (220V), use an incandescent lamp as the load, make LED1 and LED2 both go out, and the incandescent lamp lights up, then adjust the voltage regulator to the upper limit value or lower limit value, adjust RP1 or RP2 makes LED1 or LED2 just light up, and the incandescent lamp goes out, which means the debugging is successful. All components can be installed in a small plastic box. Drill two holes in the lid to fix the light-emitting diodes, drill a larger round hole to fix the piezoelectric ceramic piece, and use a suitable bottle cap to help the piezoelectric piece. The vocal cavity makes it have a louder chirping sound.