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555 AC voltage regulator delay and over-voltage alarm circui

2015-02-01 06:51  
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555 AC voltage regulator delay and over-voltage alarm circuit
This set has the function of over voltage self protection. When AC voltage regulator works abnormally and output voltage is too high, it can realize automatic displaying, alarming and cutting off high voltage, as shown in diagram 21-17. This circuit consists of high voltage delay circuit, over voltage detect, alarming circuit and output control circuit. High voltage delay circuit: delay oscillation circuit consists of 555 and R7, C4, etc. When itis AC power supplied, the voltage on C4 can not break, pin 2 voltage is low level, meanwhile pin 3 of 555 oscillator is high level, it makes VT1 break over, relay Jo pulls in, DC high voltage of constant voltage source is cut off. Due to high capacity capacitor C4 charges, after about 1 minutes, voltage on capacitor is higher than 1/3Vdd, 555's output end (pin 3) changes to low level because circuit wraparound, and VT1 is cut off, Jo's touch spot Jo-1 and Jo-2 are reset, high voltage is turned on, red indicator is lit. Over voltage detection, alarming circuit: multivibrator type oscillator consists of IC2, R10, RP2, C6, etc. When the voltage of over voltage protection signal thattaken out fromvoltage divider composed of R1, RP1 and R2 exceed given value, controlled silicon SCR breaks over, Jo is pull in, and it can cut off the high voltage of regulated power supply. At the same time, VT1 breaks over, pin 1 of 555 circuit is connected with power supply ground, 555 is Oscillating. Oscillating frequency can adjust by RP2. Sound signal sends out by piezoceramic buzzers. Output control circuit: it consists of controlled silicon SCR, relay Jo, D7, etc.