Claims
- 1. A circuit protection apparatus, comprising:
first and second terminals configured to be coupled to respective first and second circuit nodes of a circuit; a clamp circuit; and a switching circuit operative to intermittently couple the clamp circuit between the first and second terminals.
- 2. An apparatus according to claim 1, wherein the switching circuit is operative to intermittently couple the clamp circuit between the first and second terminals responsive to a voltage at at least one of the first and second terminals.
- 3. An apparatus according to claim 2, wherein the switching circuit comprises:
a switch operative to couple and decouple the clamp circuit between the first and second terminals responsive to a control input applied thereto; and a control circuit operative to generate the control input responsive to a voltage at at least one of the first and second terminals.
- 4. An apparatus according to claim 3:
wherein the switch comprises an AC-commutated switch operative to couple the clamp circuit between the first and second terminals responsive to a trigger signal and to decouple the clamp circuit from between the first and second terminals responsive to a voltage across the switch; and wherein the control circuit comprises a trigger circuit, coupled to at least one of the first and second terminals, that generates the trigger signal responsive to a voltage at at least one of the first and second terminals.
- 5. An apparatus according to claim 4, wherein the AC-commutated switch comprises a thyristor.
- 6. An apparatus according to claim 5, wherein the thyristor comprises a triac.
- 7. An apparatus according to claim 5, wherein the thyristor comprises a first thyristor, and wherein the trigger circuit comprises a second thyristor.
- 8. An apparatus according to claim 7, wherein the second thyristor comprises a diac.
- 9. An apparatus according to claim 3:
wherein the switch comprises a transistor operative to couple and decouple the clamp circuit between the first and second terminals responsive to a control signal applied thereto; and wherein the control circuit generates the control signal responsive to a voltage at at least one of the first and second terminals.
- 10. An apparatus according to claim 9:
wherein the transistor comprises a MOSFET operative to couple and decouple the clamp circuit between the first and second terminals responsive to a gate drive signal; and wherein the control circuit generates the gate drive signal responsive to a voltage at least one of the first and second terminals.
- 11. An apparatus according to claim 1, wherein the clamp circuit comprises at least one of a metal oxide varistor (MOV) and a silicon avalanche suppressor (SAS).
- 12. An apparatus for protecting a line from overvoltage, the apparatus comprising:
a first terminal configured to be coupled to the line; a second terminal configured to be coupled to a circuit node; a metal oxide varistor (MOV); and a switching circuit coupled to the MOV and to the first and second terminals and operative to intermittently couple the MOV between the first and second terminals.
- 13. An apparatus according to claim 12, wherein the circuit node comprises a ground.
- 14. An apparatus according to claim 12, wherein the line operates at a nominal voltage that, if continuously applied across the MOV for a sufficiently long time, would cause a power rating of the MOV to be exceeded.
- 15. An apparatus according to claim 12, wherein the switching circuit is operative to intermittently couple the MOV between the first and second terminals responsive to a voltage at the first terminal.
- 16. An apparatus according to claim 15, wherein the switching circuit comprises:
an AC-commutated switch operative to couple the MOV between the first and second terminals responsive to a trigger signal and to decouple the MOV from between the first and second terminals responsive to a voltage at the first terminal; and a trigger circuit operative to generate the trigger signal responsive to a voltage at the first terminal.
- 17. An apparatus according to claim 16, wherein the AC-commutated switch comprises a thyristor having a trigger terminal that receives the trigger signal.
- 18. An apparatus according to claim 17, wherein the thyristor comprises a triac.
- 19. An apparatus according to claim 17, wherein the thyristor comprises a first thyristor, and wherein the trigger circuit comprises a second thyristor coupled to a trigger terminal of the first thyristor.
- 20. An apparatus according to claim 19, wherein the second thyristor comprises one of a diac and a sidac coupled between the first terminal and the trigger terminal of the first thyristor.
- 21. An apparatus according to claim 12, wherein the switching circuit comprises:
a switch operative to couple and decouple the MOV between the first and second terminals responsive to a control signal; and a control circuit that generates the control signal responsive to a voltage at the first terminal.
- 22. An apparatus according to claim 21, wherein the switch comprises a transistor.
- 23. A method of protecting a line from voltage transients, the method comprising:
coupling a clamp circuit between the line and a circuit node responsive to a voltage on the line increasing above a first predetermined threshold; and then decoupling the clamp circuit from between the line and the circuit node responsive to the voltage on the line falling below a second predetermined threshold.
- 24. A method according to claim 23, wherein the circuit node comprises a ground.
- 25. A method according to claim 23, wherein the clamp circuit comprises at least one of a metal oxide varistor (MOV) and a silicon avalanche suppressor (SAS).
- 26. A method according to claim 23, wherein the step of decoupling comprises the step of decoupling the clamp circuit from between the line and the circuit node responsive to a zero-crossing of the voltage on the line.
- 27. A method according to claim 23, wherein the clamp circuit comprises an MOV, and wherein the step of coupling is preceded by regulating the voltage on the line to a nominal voltage that, if continuously applied across the MOV for a sufficiently long time, would cause a power rating of the MOV to be exceeded.
RELATED APPLICATION
[0001] This application claims the benefit of provisional application No. 60/286,733, filed Apr. 25, 2001, the disclosure of which is hereby incorporated herein by reference.
Provisional Applications (1)
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Number |
Date |
Country |
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60286733 |
Apr 2001 |
US |