Patent ID: 6104585
Filing Date: 2000-08-15
Classification: H05B

Abstract:
A protection circuit for a tap-grounded leakage transformer which is supplied at its primary coil with AC power across power supply terminals and lights a plurality of series-connected gas-filled lamps connected between outer ends of two secondary coils having their inner ends connected to grounding terminals, respectively, the intermediate point between said gas-filled lamps being grounded, said protection circuit comprising:first and second tertiary coils placed near said two secondary coils, respectively, and magnetically coupled therewith;first and second voltage detector circuits for detecting voltages induced in said two tertiary coils, respectively;reference voltage generating means for generating a reference voltage;first and second comparator means for comparing the detected voltages of said first and second voltage detector circuits with said reference voltage to decide if they are higher or lower than said reference voltage; andinput power shut-off means which is supplied with the decision outputs from said first and second comparator means and, when the decision result from at least one of them differs from the decision result under normal operating conditions, shuts off the supply of said AC power to said primary coil of said transformer.