SCR Crowbar Overvoltage Protection Circuit Explained

This page covers the SCR crowbar overvoltage circuit. It describes the working operation of the SCR crowbar circuit. SCR is a three-terminal device with its terminals marked as anode, cathode, and gate.

We already know that overvoltage protection is one of the essential features of power supply design. This is because the power supply is used to deliver power to very sensitive electronic, digital, and microwave components. The circuit shown below is very useful to protect digital circuits comprising of TTL logic devices.

TTL circuits require about +5V for their operation. Any voltage much beyond this voltage can damage the circuit and its components. This will result in malfunctioning or a fault in the main system where these TTL components have been used. This will result into wastage of both time and money as efforts are required to replace the faulty system with the healthy system.

The SCR crowbar overvoltage protection circuit mentioned below will help overcome this situation.

Operational Working of SCR Crowbar Circuit

SCR overvoltage crowbar circuit

• As shown in the figure, the SCR crowbar circuit consists of a Zener diode, resistor, and SCR.
• Current will flow through the resistor when the output voltage, due to some reasons, exceeds the breakdown voltage of the Zener diode.
• This flow of current will produce enough voltage in order to trigger the SCR.
• When the SCR enters the ON state, it will result in a short circuit and hence protects the load circuit.
• This short circuit remains as it is unless the power supply is switched OFF and consecutively reset.