Inexpensive single-shot crowbar for high-power applications

Crowbar switches are frequently employed in pulsed-power circuits in which a capacitor bank is discharged into a load. By forming a very low-impedance short circuit, they provide a free-wheel path for the load current and prevent an excessive build up of reverse voltage on the capacitor. Single-shot high-current crowbars commonly use either the explosive fusing of a conductor carrying the main circuit current or the controlled firing of a detonator circuit to form the required short circuit. This paper presents a new crowbar switch that is voltage activated and, unlike conventional crowbar switches, closure is initiated shortly after the voltage across it moves outside a pre-set range. No additional series-connected circuitry is necessary and there is negligible effect on the circuit prior to closure. Semiconductor devices, connected between the conductors to be short-circuited, have a rating such that they explode very shortly after the voltage first reverses. The explosion breaks through the layers of insulation that separate the devices from the conductors and so forms a low-impedance short circuit between these conductors. (4 pages)