Patent ID: 7477020

Claim:
An electronic ballast comprising: an inductor electrically coupled to a DC power supply; an output transformer; at least two switching elements; a control circuit having a resonant capacitor and electrically connected to said inductor, said output transformer and said at least two switching elements for controlling on/off statuses of said at least two switching elements; a clamping circuit electrically connected to said inductor, and limiting a node voltage among said inductor, said control circuit and said clamping circuit below a threshold value and generating an output current on condition that said node voltage is larger than said threshold value; and at least two return circuits, each of which is electrically connected to said clamping circuit and coupled to both terminals of one of said at least two switching elements for transmitting said output current to pass said output transformer and return to said clamping circuit on condition that said node voltage is larger than said threshold value, thereby permitting a reverse voltage of said at least two switching elements within a maximum allowable range of said at least two switching elements.