Limitation of current absorption under short-to-plus unpowered conditions of the output node of an amplifier

摘要

A transistor in an output stage has an emitter connected to a supply rail and a collector connected to an output node. The transistor is protected against the effects of accidental shortcircuiting of the output node of the output stage with a positive pole of a battery while the circuit is unpowered, by a protection transistor of the same type as the transistor to be protected. The protection transistor has an emitter connected to the base of the output transistor, a collector connected to the output node of the output stage, and a base connected through a biasing resistance to the supply rail on the output stage. The protection transistor and an interdigitated structure of the transistor may be formed within the same pocket, thus reducing the required area.