Crowbar device and multistage crowbar apparatus

A crowbar device having a first terminal and a second terminal, the terminals being connectible to a medium to high impedance AC voltage source, the crowbar device comprising:

• a trigger circuit connected between the first terminal and the second terminal and configured to output a trigger signal responsive to exceeding a threshold voltage across at least one trigger element of the trigger circuit;
• a signaling circuit configured to output a clamping signal according to a positive-voltage signal input from the trigger circuit;
• an overvoltage clamping circuit comprising a controllable semiconductor element connected between the first terminal and the second terminal, the overvoltage clamping circuit being configured to control the semiconductor element to be in a conducting state when the clamping signal from the signaling circuit is present, and configured to control the semiconductor element to be in a non-conducting state when the clamping signal has not been present for a predetermined time period;
• and
• a diode connected, in a reverse direction, between an interconnection within the trigger circuit and an element of the overvoltage clamping circuit, wherein the predetermined time period is at least partially determined by a time constant of the diode.

A crowbar device having a first terminal and a second terminal, the terminals being connectible to a medium to high impedance AC voltage source, the crowbar device comprising:

• a trigger circuit connected between the first terminal and the second terminal and configured to output a trigger signal responsive to exceeding a threshold voltage across at least one trigger element of the trigger circuit;
• a signaling circuit comprising a diode, the signaling circuit configured to output a clamping signal according to a signal input from the trigger circuit;
• a overvoltage clamping circuit comprising a controllable semiconductor element connected between the first terminal and the second terminal, the overvoltage clamping circuit being configured to control the semiconductor element to be in a conducting state when the clamping signal from the signaling circuit is present, and configured to control the semiconductor element to be in a non-conducting state when the clamping signal has not been present for a predetermined time period, the overvoltage clamping circuit further comprising a reverse-connected voltage limiting diode,
• the diode of the signaling circuit diode connected, in the forward direction, between a terminal of the trigger circuit and a control terminal of the semiconductor element, and
• the diode of the signaling circuit configured to have a slower switching characteristic than the voltage-limiting diode of the overvoltage clamping circuit.