A high voltage converter circuit for an implantable cardiac device. The circuit includes a plurality of transistors that are connected in parallel to a battery and the primary winding of a transformer. A switching element is connected to the circuit so as to periodically connect and disconnect the capacitors to the primary winding of the transformer to thereby induce the capacitors to be charged and periodically discharged across the transformer into charging capacitors. A circuit also preferably includes a disconnect circuit that will disconnect the capacitors from the battery during periods of non-use to inhibit unwanted dissipation of the battery's energy.