Patent ID: 6856137

Claim:
An AC ground fault detector system for sensing an AC signal indicative of an unintended electrical path between a load driven by a DC power source and a reference potential, said system comprising: a first power conductor coupled to a first terminal of said power source; a second power conductor coupled to a second terminal of said power source; a switching mechanism coupled to the first and second power conductors and operative for alternately connecting a phase of said load with the first and second power conductors according to a predetermined switching rate, whereby, during normal operation, voltages developed at the first power conductor and second power conductor are substantially constant with respect to a reference; and whereby, in the event of an occurrence of said unintended electrical path of at least one phase of the load with the reference potential, time varying voltages are developed at the first power conductor and second power conductor associated with the switching rate; a detector comprising an input port coupled to the first power conductor for receiving the voltage or current signal on the first power conductor and having a capacitor coupled to said input port, said capacitor operable for performing one of a charging and discharging operation in response to said time varying voltage signal, said capacitor being coupled to said reference potential through an impedance device or transformer for generating a detected signal; a processing circuit for processing said detected signal and comparing with a threshold value; and an output port for generating an output signal based on said comparison; whereby the occurrence of the unintended electrical path between the load and reference potential causes a change in the voltage or current signal on the first power conductor of sufficient magnitude relative to the threshold value for detection by said detector such that the output signal of the detector is indicative of a detected fault.