Patent ID: 7450995

Claim:
An output circuit for use in an implantable cardiac device comprising: an output adapted for connection across a load; a charging circuit; a first capacitor switchably coupled between the charging circuit and the output; a second capacitor switchably coupled across the first capacitor and the output; a pulse-width modulation circuit that generates first and second pulse-width modulation control signals; a polarity control circuit that generates first and second polarity control signals; an H-bridge including a first leg and a second leg, each leg including a pulse-width modulation switch and a polarity switch, wherein: the pulse-width modulation switches are configured to receive a respective one of the first and second pulse-width modulation control signals, and alternately switch between a closed state and an open state in response to the pulse-width modulation control signal; and the polarity switches are configured to receive a respective one of the first and second polarity control signals and switch between a closed state and an open state in response to the polarity control signal; and a controller programmed to: control the polarity control circuit to generate first and second polarity control signals whereby the polarity switch of the first leg is closed and the polarity switch of the second leg is open, and control the pulse-width modulation circuit to generate first and second pulse-width modulation control signals whereby the pulse width modulation switch of the first leg is open and the pulse width modulation switch of the second leg is closed, and the first capacitor is thereby electrically coupled across the second capacitor and the output in a first polarity; and while the first capacitor is electrically coupled across the second capacitor and the output in the first polarity, further control the pulse-width modulation circuit to generate pulse-width modulation control signals whereby the pulse width modulation switch of the second leg is toggled between open, whereby the first capacitor is electrically decoupled across the second capacitor and the output, and the second capacitor is electrically coupled across the output, and closed, whereby the first capacitor is electrically coupled across the second capacitor and the output.