Reverse Bias Protection for 78xx and 79xx Series Voltage Regulators

          We have already seen 78xx positive voltage regulators and 79xx series negative voltage regulators. One thing we have missed in those circuits is the reverse-bias protection system. This type of protection system is necessary when the input voltage collapse faster than the output voltage. If the output voltage is approximately more than 7V, emitter base junction of the internal or external series pass element get break down and get damaged. Normally a shunt diode is used to prevent this. Shunt diode is connected in such a way that the input supply will reverse bias the diode.

          First circuit is the reverse bias protection circuit for 78xx series and second circuit is the reverse bias protection circuit for 79xx series. Diode is normally connected across the input and output pin of the integrated circuit in such a way that, input will reverse bias the diode. Diode used here is 1N4001.