H-bridge circuit for generating a high-energy biphasic and external pacing waveform in an external defibrillator

Abstract

A circuit for generating both a biphasic defibrillation waveform and an external pacing waveform in an external defibrillator is provided. The output circuit of the device utilizes one or more SCR switches for applying energy to a patient. In one embodiment, the output circuit is in the form of an H-bridge, with three SCR legs and one IGBT leg. A drive circuit for one of the SCR legs is provided such that the SCR may be continuously driven on for either a high energy biphasic defibrillation pulse or a low energy pacing pulse. In one embodiment, the output circuit conducts the pacing waveform through a combination of one upper leg SCR of the H-bridge and a current source. The current source is configured to bypass a lower leg SCR of the H-bridge. The output circuit is capable of conducting pacing currents of as low as 10 mA. The output circuit is also capable of conducting a high energy biphasic defibrillation waveform of as high as 200 or more joules, and also a low energy defibrillation pulse of as low as 1 to 50 joules. The output circuit is also capable of conducting currents as high as approximately 200 amperes.