Patent ID: 7944149

Claim:
A ballast for providing power to a lamp, said ballast comprising: a direct current (DC) bus having a positive node and a negative node; a first switch having a high side, a control terminal, and a low side, wherein the high side of the first switch is connected to the positive node of the DC bus; a second switch having a high side, a control terminal, and a low side, wherein the low side of the second switch is connected to the negative node of the DC bus, and the high side of the second switch is connected to the low side of the first switch forming a first midpoint; a third switch having a high side, a control terminal, and a low side, wherein the high side of the third switch is connected to the positive node of the DC bus; a fourth switch having a high side, a control terminal, and a low side, wherein the low side of the fourth switch is connected to the negative node of the DC bus, and the high side of the fourth switch is connected to the low side of the third switch forming a second midpoint; a filter circuit connected between the first midpoint and the second midpoint, said filter circuit comprising: a capacitor connected in parallel with the lamp; and a transformer having a buck inductor as a primary winding and having a secondary winding, said buck inductor connected in series with the capacitor; a controller connected to the control terminals of the first, second, third, and fourth switches for controlling the first, second, third, and fourth switches to provide an open circuit voltage across the lamp prior to ignition of the lamp, wherein the controller receives power from the buck inductor via the secondary winding of the transformer.