Patent ID: 6154081
Filing Date: 2000-11-28
Classification: H02H,H03K

Abstract:
A protected load circuit powered by a power source having first and second polarity terminals, comprising:first and second load circuit terminals normally connected to the first and second terminals of said power source, respectively;a load circuit including an electrical load, a load switching device, and a protection transistor connected in series, the electrical load being electrically coupled to the first load circuit terminal, and the protection transistor being electrically coupled to the second load circuit terminal, the protection transistor being effective in a conductive state to electrically couple said load switching device to the second load circuit terminal, and in a non-conductive state to electrically isolate the load switching device from the second load circuit terminal;a capacitor coupled to a control terminal of said protection transistor, said capacitor being effective when charged to bias said protection transistor to said conductive state, and when discharged to bias said protection transistor to said non-conductive state;a charging circuit for charging said capacitor to bias said protection transistor to said conductive state when the first and second load circuit terminals are connected to the first and second polarity terminal of said power source, respectively, but for allowing said capacitor to bias said protection transistor to said non-conductive state when the first and second polarity terminals of said power source are reversed; anda discharging circuit for discharging said capacitor during a discharge interval when the voltage across said load circuit is momentarily reversed due to a disconnection of said power source, thereby allowing said protection transistor to remain in said conductive state during said discharge interval for protecting said load switching device from damage due to the momentary voltage reversal.