MOS protection device

Claim 1

An MOS device for self-protection from overvoltage, comprising: a drain region of a first conductivity type; a plurality of base regions of a second conductivity type, formed in said drain region; at least one source region, of said first conductivity type, formed in at least one of said base regions, each of said at least one source region being located with a preselected spacing from said drain region; a first electrode and a second electrode for making electrical connection to said device, said first electrode region and said at least one base region, and said second electrode in electrical contact with said drain region; a gate electrode in direct electrical contact with a base region electrically isolated from said at least one base region contacted by said first electrode; and a diode junction formed between said electrically isolated base region and said drain region, said junction having an avalanche voltage level chosen to cause voltage breakdown to occur between said second electrode and said gate electrode at a lower voltage level than a breakdown voltage level present between said second electrode and said first electrode when said chosen avalanche voltage level is exceeded, so as to cause a resulting avalanche current to be conducted to said gate electrode when said chosen avalanche voltage is exceeded and to cause further device current to be conducted through at least one uniform and controlled alternate current path formed between said first and second electrodes: said device further comprising impedance means coupled between said gate and first electrodes for controlling the magnitude of said avalanche current and for preventing said device from becoming prematurely conductive due to an allowable leakage current.