Patent ID: 6094332
Filing Date: 2000-07-25
Classification: H01L

Abstract:
A protection circuit for protecting a main circuit having field effect transistors against abnormal voltage comprising:a first field effect transistor electrically connected between a first power supply line and a second power supply line different in potential level from each other and caused to turn on for discharging current from said first power supply line to said second power supply line when said abnormal voltage is applied between said first power supply line and said second power supply line, said first field effect transistor forming a part of a first discharging path connected between said first power supply line and said second power supply line;a second field effect transistor connected between said first power supply line and said second power supply line to form a part of a second discharging path connected between said first power supply line and said second power supply line, wherein a part of said current flows from a source electrode of said second field effect transistor to a drain electrode of said second field effect transistor, said first field effect transistor and said second field effect transistor fabricated concurrently with said field effect transistors of said main circuit to guarantee a relationship between break-down voltages of said field effect transistors; anda clamping diode connected between said second power supply line and a gate electrode of said second field effect transistor so as to limit a potential level at the gate electrode of said second field effect transistor below said break-down voltage of said second field effect transistor.