Over Voltage Protection Circuit, Auto Cut Circuit

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 Overvoltage autocut circuit diagram

This Autocut circuit is very easy, simple and very useful.

Only One transistor and some other components are used in this high-voltage protection Auto circuit.

The load is connected with the NC (normally connected ) Pin of the relay.

This circuit is a very useful auto-cut circuit to protect of any electrical or electronic appliance from high voltage. If any device needs 12v to work properly then this can be damaged by increasing the voltage. This circuit automatically cuts the current supply to any appliance from the input circuit. And when the voltage decreased at a normal level then automatic on the supply is. So it helps to protect the circuit from damage by the high voltage. If you use this circuit for Autocut on over 6v then use 6 v relay and the circuit need 6v.

overvoltage auto cutoff protection circuitBefore using this circuit set the preset and check the relay or output to at which the input voltage level relay gets activated. Increase and Check the input voltage by multimeter and set the preset at the required position. This circuit can be used at both AC and DC appliances because it uses a relay, but this circuit works only on DC supply power.


At first, when the voltage is under or below the maximum limit ( at which it is adjusted) the maximum voltage drops through the Resistor R2 to the ground and the Base of the Transistor does not get enough power to switch on the transistor. At this stage, the transistor in an OFF state, and Relay does not get supplied and it is not activated.

when the Input voltage of this circuit is increasing and cross a level then the input voltage through resistor R1 and preset also increased and even after dropping the voltage through R3, enough amount of voltage is at the Base of the Transistor Turned On it and Supply passed Between Emitter and collector. Now Relay is activated and the supply is Disconnected to the appliance. And that is protected from high voltage supply.

Before using it should be adjusted by preset and tested the input voltage and set required the auto cut level according to suitable.


Transformer 12-0-12v 1A -1

BC547 Transistor – 1

1000uf 35v capacitor -1

1N4007 Diode – 1


2.2kΩ-2,    33kΩ – 1   

Preset – 5K- 1

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