High voltage protection using scrs

Abstract

A high voltage protection circuit includes a breakdown network for providing a discharge path between a pair of terminal of a circuit to be protected. Each network conducts current between a supply terminal and another terminal at a low threshold voltage value when power is removed from the supply terminal. The network increases the threshold value when power is applied to the supply terminal to prevent conduction through the breakdown network during normal operation of the circuit to be protected. In one implementation, the protection circuit includes anti-latching circuitry connected to the breakdown network for preventing the breakdown network from latching on after or during the time power is applied to the supply terminals. To minimize the degradation of DC operating characteristics, the leakage currents, due to the protection circuit, between the first terminal and the positive supply terminal, and between the first terminal and the negative supply terminal cancel each other. The protection circuit may be incorporated on the same substrate as the circuit to be protected or it may be incorporated on a separate substrate sharing a common housing with the circuit to be protected. Alternately, the protection circuit may be in its own housing with its external leads connected to the leads of a first housing including the circuit to be protected.