Crowbar device and multistage crowbar apparatus
A crowbar device has a first terminal and a second terminal, the terminals being connectible to a medium to high impedance AC voltage source including a trigger circuit configured to output a trigger signal responsive to exceeding a threshold voltage across at least one trigger element of the trigger circuit; a positive-side signaling circuit and a negative-side signaling circuit configured to output a positive or a negative clamping signal, respectively, according to a positive-voltage or a negative-voltage signal, respectively, input from the trigger circuit; and a positive-side overvoltage clamping circuit and a negative-side overvoltage clamping circuit configured to control their respective semiconductor element to be in a conducting state, when the clamping signal from the corresponding signaling circuit is present, and configured to control their semiconductor element to be in a non-conducting state, when the corresponding clamping signal has not been present for a predetermined time period.
1. 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 positive-side signaling circuit configured to output a positive clamping signal according to a positive-voltage signal input from the trigger circuit;
a positive-side overvoltage clamping circuit comprising a controllable semiconductor element connected between the first terminal and the second terminal, the positive-side overvoltage clamping circuit being configured to control the semiconductor element to be in a conducting state when the positive clamping signal from the positive-side signaling circuit is present, and configured to control the semiconductor element to be in a non-conducting state when the positive clamping signal has not been present for a predetermined time period;
a negative-side signaling circuit configured to output a negative clamping signal according to a negative-voltage signal input from the trigger circuit;
a negative-side overvoltage clamping circuit comprising a controllable semiconductor element connected between the first terminal and the second terminal, the negative-side overvoltage clamping circuit being configured to control the semiconductor element to be in a conducting state when the negative clamping signal from the negative-side signaling circuit is present, and configured to control the semiconductor element to be in a non-conducting state when the negative 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 one of the positive-side overvoltage clamping circuit and the negative-side overvoltage clamping circuit, the predetermined time period at least partially determined by a time constant of the diode.
2. The crowbar device according to claim 1 ,
wherein the positive-side signaling circuit is configured to output the positive clamping signal according to a time derivative of a current of the positive-voltage signal.
3. The crowbar device according to claim 1 ,
wherein the predetermined time period is selected to be at least as long as a cycle determined by a frequency of the AC voltage source.
4. The crowbar device according to claim 1 ,
wherein the trigger circuit comprises a stack of serially-connected trigger elements, the trigger circuit being configured to output the trigger signal responsive to exceeding the threshold voltage across the stack of serially-connected trigger elements.
5. The crowbar device according to claim 4 ,
wherein the diode is connected, in a reverse direction, between an interconnection within the stack of serially-connected trigger elements and the element of at least one of the positive-side overvoltage clamping circuit and the negative-side overvoltage clamping circuit.
6. The crowbar device according to claim 1 ,
wherein the at least one trigger element comprises at least one of a spark gap, a DIAC, and a SID AC.
7. The crowbar device according to claim 1 ,
wherein at least one of the controllable semiconductor element of the positive-side overvoltage clamping circuit and the controllable semiconductor element of the negative-side overvoltage clamping circuit comprises a transistor.
8. The crowbar device according to claim 1 ,
wherein the positive-side signaling circuit comprises a diode connected, in the forward direction, between a terminal of the trigger circuit and a control terminal of the semiconductor element of the positive-side overvoltage clamping circuit.
9. The crowbar device according to claim 8 ,
wherein the positive-side overvoltage clamping circuit and the negative-side overvoltage clamping circuit each comprises a reverse-connected voltage-limiting diode, connected such as to limit a voltage at the control terminal of the respective semiconductor element.
10. The crowbar device according to claim 9 ,
wherein at least one of the diode of the positive-side signaling circuit and the diode of the negative-side signaling circuit is configured to have a slower switching characteristic than the respective reverse-connected voltage-limiting diode of at least one of the positive-side overvoltage clamping circuit and the negative-side overvoltage clamping circuit.
11. The crowbar device according to claim 1 , being configured to be functional only by an AC voltage supplied externally to the first and second terminals.
12. The crowbar device according to claim 1 , wherein at least one of the semiconductor element of the positive-side overvoltage clamping circuit and the semiconductor element of the negative-side overvoltage clamping circuit is configured to be in a conducting state when the voltage source is in a failure state.
13. The crowbar device according to claim 7 , wherein the transistor comprises a MOSFET.
14. The crowbar device according to claim 9 , wherein the voltage-limiting diode comprises a Zener diode.
15. The crowbar device according to claim 1 ,
wherein the negative-side signaling circuit is configured to output the negative clamping signal according to a time derivative of a current of the negative-voltage signal.
16. The crowbar device according to claim 1 ,
wherein the negative-side signaling circuit comprises a diode connected, in the forward direction, between a terminal of the trigger circuit and a control terminal of the semiconductor element of the negative-side overvoltage clamping circuit.
17. 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.
18. 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.