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Abstract

An external defibrillator (8) with an output circuit (14) having four legs arrayed in the form of an 'H' (an 'H-bridge') is disclosed. Each leg of the output circuit contains a solid-state switch (31, 32, 33, 34). 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 (51, 53, 54) 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 (52) 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 (52) 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.

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