High current drain-to-gate clamp/gate-to-source clamp for external power MOS transistors

摘要

An external FET (12) has protection provided thereto for excessive voltages between the gate and drain and between the gate and source. A drain-to-gate clamp is provided with a plurality of series connected zener diodes (34), (36) and (38) which are connected in series with a Schottky diode (42). The current therethrough is sensed with a resistor (56) which turns on a bypass transistor (58) to shunt current around the zener diodes when an excess voltage causes them to break down. This will turn on the FET (12). The gate-to-source clamp is configured with two zener diodes (74) and (76) which are reversed biased. A series current sense resistor (82) senses the current through the diodes and turns on a transistor (84) when the current exceeds a predetermined level. This will effectively shunt current around the zener diodes (74) and (76).