is a lowering of the cmp dc value to a nominal or minimum value i e cmp vmin so that a high voltage condition is not appearing on the transformer tx 1 thus the crossover point 36 is shifted to the left thereby decreasing the amount of overlap between complementary switches recall switch_c is turned on at the intersection point 36 likewise current sense comparator 42 is connected to the frequency generator 22 to turn the generator 22 off when the sense value is 0 or some other preset value indicative of an open circuit condition the cmp is fed into the protection circuit 62 this is to shut off the frequency sweeper 22 if the ccfl is removed during operation open circuit condition to protect the circuit from an over voltage condition the present embodiment preferably includes protection circuit 60 the operation of which is provided below the description of the over current protection through the current sense comparator 42 is provided above the circuit 60 includes a protection comparator 62 which compares signal cmp with a voltage signal 66 derived from the load 20 preferably voltage signal is derived from the voltage divider c 2 and c 3 i e in parallel with load 20 as shown in fig2 in the open lamp condition the frequency sweeper continues sweeping until the ovp signal 66 reaches a threshold the ovp signal 62 is taken at the output capacitor divider c 2 and c 3 to detect the voltage at the output of the transformer tx 1 to simplify the analysis these capacitors also represent the lump capacitor of the equivalent load capacitance the threshold is a reference and circuit is being designed so that the voltage at the secondary side of the transformer is greater than the minimum striking.