Mains voltage bidirectional limit alarm protection circuit diagram

  
When the alarm protection can be higher or lower than the predetermined value in the mains voltage, sound and light alarm,
Mains voltage bidirectional limit alarm protection circuit diagram - schematic

and automatically cut off the electrical power, electrical protection is not damaged. The device is small, full-featured, making simple and practical. Circuit shown in Figure 1. Mains voltage all the way from C3 Buck, DW regulator, VD6, VD7, C2 rectifier output stable 12V DC voltage supply circuit. Another route VD1 rectified, R1 buck, C1 filtered to produce about 10.5V voltage detection mains voltage variations in the input signal on RP1, RP2. Door IC1A, IC1B composition overvoltage detection circuit, IC1C undervoltage detection, IC1D switching, IC1E, IC1F and YD piezoelectric ceramics composed audio pulse oscillator. VT transistors and other components and relay J circuit protection action. LED1 red for mains overvoltage indication LED2 green pipe for mains voltage indicator.Mains normal, non IC1A output high, IC1B, IC1C output low, LED1, LED2 are turned off does not emit light, VT cutoff, J does not operate, the normal electrical power supply, then point B is high, F4 output low, VD5 conduction, C point is low, audio pulse oscillator to stop, YD not sound. When the mains overvoltage or undervoltage, IC1B, IC1C which has a high output, so point A goes high, VT saturated conduction, J pull power, disconnect the electrical power supply, the point B becomes low potential, IC1D output high, VD5 off, reverse resistance is large, the equivalent of an open circuit, audio pulse oscillator start-up, YD alarm will sound, and the corresponding light-emitting diode light indication. When debugging, using a power supply regulator, the voltage regulator is normal (220V), with an incandescent lamp as a load, make LED1, LED2 are off, incandescent light, and then the upper or lower limit on the regulator raised , adjust RP1 or RP2 make LED1 or LED2 just light, incandescent lamp off, the successful commissioning.All components can be installed in a small plastic box, will play two holes fixed LEDs on the lid, make a little hole larger fixed piezoelectric ceramics, and with an appropriate cap to the piezoelectric substrate was used as an aid tune to have loud chirping.




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