Patent ID: 7199988

Claim:
A discharge tube lighting transformer apparatus with a protection circuit against non-grounding of a ground terminal comprising: a transformer having a primary winding, a secondary winding with a mid-point and unbalancing means for causing voltages induced across windings disposed on the opposite sides of the mid-point of the secondary winding to be unbalanced relative to each other; a ground fault detection circuit connected between the mid-point of the secondary winding and a ground terminal of the transformer for detecting, if one occurs, a ground fault in a connection wiring which connects discharge tubes across the secondary winding while the ground terminal is grounded as normal state, to thereby generate a detection output; a hot line terminal and a non-active line terminal to be connected to a non-grounded side and a ground side of A.C. power source, respectively; a non-grounding protection circuit connected between the non-active line terminal and the ground terminal for detecting if a voltage appearing between the non-active line terminal and the ground terminal is larger than A.C. voltage of the A.C. power source applied across the non-active line terminal and the hot line terminal, to thereby generate a detection output; and power source interrupting means controlled operatively by one of the detection outputs from the non-grounding protection circuit and the ground fault detection circuit to operatively interrupt the supply of the A.C. power from the hot line terminal and the non-active line terminal to the primary winding.