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555 long time delay circuit 1

2015-01-28 18:04  
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555 long time delay circuit 1
As the figure 6-1 shown, the long time delay circuit uses 555 as the core,it usesa high-impedance op-amp CA3140 buffer amplifier, the feedback bootstrap circuit to maintain a constant charging current, to ensure the accuracy of linear and time of charge voltage. When the pin 2 of 555 is triggered by the low level or the switch is closed to ground, the 555 sets, pin 3 is in high level, so that one of the four analog switches CC4066 S1 is conducted, S2 turns off, C1 charges through R3, R4. The bootstrap circuit produced by feedback op amp keeps the voltage when the both ends of the high-resistance R1 in the charging process. It ensures a linear charging. The current flowing R4 the charging circuit is about 10mA. CA3140(IC2) is a high-gain low-drift op amp, it is usedas buffer amplifier, the feedback forms the bootstrap circuit. The S4 is mandatory reset switch.