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Mains supply overvoltage protection circuit with good perfor

2016-09-22 04:02  
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Mains supply overvoltage protection circuit with good performance
Mains supply overvoltage protection circuit with good performance
In electric power lacking areas, the power supply is very unstable, the peak value is only about 170V, at night, it is over 250V, in order to protect the expanding household appliances, it is needed to deploy a overvoltage protector. The circuit is as shown, it adopts capacity depressurization and simple regulated power supply circuit, when the power supply is normal, the TL431C control pole voltage is lower than 2.5V, TL431C circuit is not conductive, realy contact is open. When the mains power reached 250V, after rectifier filter, the current is 3.3mA, the voltage drop on R3, diode and regulator tube(including LED) is 11V and 26V. 37V voltage is divided by R1, R2, then A point voltage is 2.55V, TL431C circuit turns on, relay K pull-in, mains power is a short circuit, then the power supply over current device is tripping or fuse burn-out, it can protect household appliances. To series connect a small resistance in contact loop, it can protect contact from burning off due to the overlarge short-circuit current. Because the capacitance of capacitor C3 is larger, it can store large charge to add on the relay coil, then the relay contact will keep 0.2s pull-in time, it is enough to make over current device trip or fuse burn-out.