ARRANGEMENT FOR PROTECTING LOW-VOLTAGE CONTROL CIRCUITRY FROM EXTERNALLY APPLIED HIGH VOLTAGES, AND DIMMING BALLAST EMPLOYING SUCH AN ARRANGEMENT

摘要

An arrangement for protecting low-voltage control circuitry from externally applied high voltages comprises a voltage source (30) and a current-sourcing circuit (40). Current-sourcing cicuit (40) provides current to an external controller (18) in a normal manner when an external source of high voltage is not applied to the output connections (42, 44), protects itself (40) and the voltage source (30) from damage when an external source of high voltage is applied to the output connections (42,44), and provides current to the external controller (18) in a normal manner after the external source of high voltage is subsequently removed from the output connections (42, 44). The arrangement may be employed as the dimming interface circuit (900) of an electronic dimming ballast (60) for gas discharge lamps to protect ballast circuitry from damage due to wiring errors during installation.