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SCR crowbar circuit | SCR crowbar overvoltage circuit

This page covers SCR crowbar overvoltage circuit. The page describes working operation of SCR crowbar circuit.

SCR is a three terminal device with its terminals marked as anade, cathode and gate. Refer SCR triggering which describes operation of SCR in forward biased state and reverse biased state.

We already know that overvoltage protection is one of the essential feature of power supply design. This is because 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 circuit comprising of TTL logic devices. TTL circuits require about +5V for its operation. Any voltage much beyond this voltage can damage the circuit and its components. This will result into malfunctioning or fault in the main system where this 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.

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 SCR crowbar circuit consists of zener diode, resistor and SCR.
• Current will flow through the resistor, when the output voltage due to some reasons exceeds breakdown voltage of the SCR.
• This flow of current will produce enough voltage in order to trigger the SCR.
• When SCR enters into ON state, it will result into short circuit and hence protects the load circuit.
• This short circuit remains as it is unless power supply is switched OFF and consecutively provided reset to it. Also refer Difference between SCR, DIAC, TRIAC, UJT >>.

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