HIGH CURRENT MOS DEVICE WITH AVALANCHE PROTECTION AND METHOD OF OPERATION

摘要

Particularly in high current applications, impact ionization induced electron-hole pairs are generated in the drain (74) of an MOS transistor (51) that can cause a parasitic bipolar transistor (38) to become destructively conductive. The holes pass through the body region (76) of the MOS transistor (51), which has intrinsic resistance, to the source (80), which is typically held at a relatively low voltage, such as ground. The hole current causes a voltage to develop in the body region (76), which acts as the base (42). This increased base voltage is what can cause the parasitic bipolar transistor (38) to become conductive. The likelihood of this is greatly reduced by developing a voltage between the source (80), which acts as the emitter (44), and the body region (76) by passing the channel current through an impedance (62) between the source (80) and the body region (76). This causes the emitter voltage to increase as the base voltage is increased and thereby prevent the parasitic bipolar transistor (38) from becoming conductive.