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The mains over-voltage protection circuit of excellent natur

2016-09-25 03:11  
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The mains over-voltage protection circuit of excellent nature
See as the figure, the circuit adopts the capacitor step-down and the simple regulated power supply circuit, when the power supply is normal, the voltage controlled by TL431C is lower than 2.5V, and TL431C is blocked, the relay is open. When the mains voltage is higher than 250V, the current which has been rectified and filtered reaches 3.3mA, the voltage drops on R3, diode and stabilivolt (including glow tube) are 11v and 26v, respectively. The 37V voltage is distributed by R1 and R2, the voltage on the distributing point is 2.55v, TL431C is conducting, the relay is pulling in, the mains is short, which make the current protector jump or the fuse blow out.