Patent ID: 8209007

Claim:
An external defibrillator comprising an H-bridge for delivering bipolar electrotherapy to a patient, the H-bridge having: (a) a respective solid state switching device in each of its four legs, the switching device in at least one of the high legs of the H-bridge including an SCR, (b) an input for applying an external control signal to the switching device in the low leg diagonally opposite said at least one high leg, wherein turning on the switching device in said diagonally opposite low leg causes a voltage increase across the SCR in said at least one high leg, and (c) a control circuit in said at least one high leg, the control circuit comprising a capacitor connected in parallel with the anode-gate path of the SCR, the capacitor having a time constant which generates a voltage spike at the gate of the SCR in response to said voltage increase across the SCR, said spike turning on the SCR, whereby the SCR is turned on without the application of an external control signal to said high leg control circuit.