Patent ID: 6856495

Claim:
A series-pass over-voltage protection circuit for supplying operating voltage to a continuously powered electrical load from a DC voltage supply that is subject to transient over-voltages, comprising: a P-channel MOSFET (PFET) having a source coupled to a positive terminal of said voltage supply, a drain coupled to said electrical load, and a gate; a first current sink that couples said gate to a negative terminal of said voltage supply and activates said PFET to supply operating voltage to said electrical load; a gate discharge amplifier including a high current capability gate discharge transistor coupled between said gate and said source; and a second current sink that responds to excessive operating voltage by sinking current from a control terminal of said gate discharge transistor to activate the gate discharge transistor to control the activation of said PFET for suppressing said operating voltage to a value that will not damage said electrical load, said first and second current sinks having a characteristic impedance that is relatively high compared to a characteristic impedance of said gate discharge amplifier and PFET so that said gate and source tend to track the transient over-voltages of said voltage supply, and such transient over-voltages do not substantially change the activation of said PFET.