Nixon & Vanderhye
Photoswitching device including a MOSFET for detecting zero voltage crossing
 A switching device includes a thyristor and a MOSFET, and a voltage clamp circuit. The voltage clamp circuit includes an N.sup.+ type contact region formed in a surface layer of a N type substrate and electrically connected to a gate electrode of a MOSFET, and a P type guard ring surrounding the contact region. 
Sharp Kabushiki Kaisha
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Mitsuru Nobuyuki
Mariyama Kato