MOS TRANSISTOR CIRCUIT WITH BREAKDOWN PROTECTION

摘要

A protected MOS transistor circuit includes a first input (or output) MOS transistor (1) and a protective circuit (10) including a second depletion mode MOS transistor (TrP) having a drain-source current path connected between ground and the gate of the MOS transistor and arranged to prevent breakdown of the gate of the protected MOS transistor when power is off as a consequence of stray voltages when power is off. A substrate voltage generating circuit is arranged to generate a substrate bias voltage which is applied to the substrate of the second MOS transistor when power is on so as to alter its threshold voltage, causing the transistor to become non-conductive.