Output stage, and automotive regulator, with supply-dependent selection

Abstract

The contrasting requirements of low power consumption during operation and ability to function under drastic drops of the supply voltage at start-up of output power stages of an electric system of self-generation and recharge of a storage battery, are satisfied by an output power driving stage composed of a bipolar transistor and a field effect transistor, functionally connected in parallel to each other and having independent control terminals. A control signal is selectably switched either to the base of the bipolar output transistor or to the gate of the field effect output transistor, depending on the level of the supply voltage. A comparator comparing the voltage present on the supply node with a reference voltage controls a selection switch. The low threshold of the bipolar transistor ensures functioning at start-up, while the field effect transistor provides a low power consumption during normal running conditions.