Solid state crowbar circuit

Claim 1

A crowbar circuit operatively connected between a power supply and a device to be protected comprising: a siliconcontrolled rectifier means adapted to be connected in parallel with an associated device to be protected, a first relay means connected in series with said rectifier means for actuating normally closed contactor means adapted for opening same and cutting off power to an associated device to be protected upon firing of said rectifier means, resistor means adapted to be connected in series with an associated device to be protected and intermediate such an associated device and said relay means, said resistor means being adapted to sense current flowing through such an associated device to be protected, variable potentiometer means connected in parallel with said resistor means, said potentiometer means being composed of at least a resistor and a movable wiper, said movable wiper being connected to a gate terminal of said rectifier means and adapted to allow a portion of a voltage developed across said resistor means to be passed to said gate terminal of said rectifier means, a second relay means connected in series with said resistor means and intermediate said resistor means and an associated device to be protected, said second relay means actuating normally open contact means connecter intermediate said gate terminal and said movable wiper and adapted to hold said rectifier means out of the system until said second relay means senses a small current from such an associated device for preventing said rectifier means from firing upon initial activation of the circuit, whereby said second relay means closes said normally open contact means upon sensing a small current from an associated device and said rectifier means switches to its low impedance state when a critical voltage is applied at said gate terminal thereby activating said relay means which in turn actuate said contactor means.