Shunt Regulator Applications Crowbar

To protect solid-state electronic equipment from overvoltage due to a power-supply component failure, it is sometimes desirable to use a ‘crowbar’ circuit. When a preset voltage is exceeded, the SCR turns on, shorting the output and blowing the fuse on the input side of the crowbar circuit. The circuit in Figure 6-44 is set to trip when VO reaches 27 V. When that occurs, the reference voltage should be 2.5 V which turns on the TL431, thus biasing the SCR low. This turns the SCR on and immediately blows the safety fuse on the circuit input, thus protecting the equipment using this power supply.

Figure 6-44. Shunt Regulator in Crowbar Circuit