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

Abstract

An external defibrillator with an output circuit having four legs arrayed in the form of an “H” (an “H-bridge”) is disclosed. The output circuit is designed to be able to conduct a range of defibrillation pulse energies, from below 50 joules to above 200 joules. Each leg of the output circuit contains a solid-state switch. By selectively switching on pairs of switches in the H-bridge, a biphasic defibrillation pulse may be applied to a patient. The switches in three of the legs of the H-bridge output circuit are preferably silicon controlled rectifiers (SCRs). Gate drive circuits are coupled to the SCRs to bias the SCRs with a voltage that allows the SCRs to remain turned-on even when conducting low current. The switch in the fourth leg is preferably a pair of insulated gate bipolar transistors (IGBTs) coupled in series. A gate drive circuit is coupled to the gate of the IGBTs to provide a slow turn-on and a fast turn-off of the IGBTs. The gate drive circuit also biases the IGBTs with a sufficient voltage to allow the IGBTs to withstand a shorted discharge of the external defibrillator through the output circuit. The circuit also includes a protective component that has both inductive and resistive properties. An internal energy dump may be performed by biasing on two legs on the same side of the H-bridge output circuit, thus eliminating the need for a separate energy dump circuit. Methods for testing the H-bridge and verifying its integrity are also disclosed.