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555 automatic reset electric shock protector circuit

2015-02-04 02:28  
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555 automatic reset electric shock protector circuit
The tube is connected to 555's trigger terminal 2 foot, ordinarily, VT1 tube cuts off, 2 foot is high level. A monostable circuit is composed of 555 and R2, C5. When VT1 tube is turned on, 2 foot level is lower than trigger level 1/3 VDD, 555 is set, 3 foot turns into high level, LED lights, relay J pulls in, the AC power supply is cut off. 555 internal discharge tube is open, C5 is charged by R2, when C5's voltage is higher than 2/3 VDD threshold level, the circuit is reset, 3 foot turns to low level, J releases, it recovers to transmit electricity. After trigger monostable, the delay time td=1.1R2C5, the figured parameter's delay time is about 10s. When the circuit has electric shock, due to VT1 tube is turned on, so 555 is in trigger delay state all the time, J can not release, the power supply is cut off.