Surge protector
A surge protection circuit having an open circuit voltage surge protector, such as a gas discharge tube (GDT), a closed circuit current surge protector, such as a thermistor, and a thyristor. The GDT has a breakdown voltage that is at least a first defined amount higher than an anticipated highest peak voltage. The thermistor has a series resistance associated with a series resistance of electrical equipment being protected and a breakdown voltage that is at least a second defined amount higher than an impulse voltage (voltage required to excite the GDT based on the breakdown voltage) for the GDT. The thyristor has a rated peak current at least a third defined amount greater than a peak current for the thermistor.
1. A method for selecting appropriate components for a surge protection circuit providing surge protection for a device, the method comprising:
determining a highest peak voltage at input to the surge protector;
selecting a gas discharge tube (GDT) having a first breakdown voltage greater than the anticipated highest peak voltage;
determining an impulse voltage for the GDT, wherein the impulse voltage is the voltage required to excite the GDT based on the GDT's breakdown voltage;
selecting a thermistor having a second breakdown voltage greater than an impulse voltage for the GDT;
determining resistance of the thermistor at the impulse voltage for the GDT;
computing an anticipated peak current of the thermistor, wherein the anticipated peak current is based on the impulse voltage for the GDT and resistance of the thermistor; and
selecting a thyristor having a rated peak current greater than the anticipated peak current for the thermistor.
2. The method of claim 1 , wherein the selecting a thermistor includes selecting the thermistor having a serial resistance of approximately 10 ohms.
3. The method of claim 1 , wherein the selecting a thermistor includes selecting a ceramic protective temperature coefficient (CPTC) thermistor.
4. The method of claim 1 , wherein the selecting a thermistor includes selecting a polymer protective temperature coefficient (PPTC).
5. The method of claim 1 , wherein the selecting a GDT, the selecting a thermistor, and the selecting a thyristor are based on a surge having a 1000 V/μs impulse voltage shape.
6. The method of claim 1 , further comprising providing the surge protection circuit having the GDT, the thermistor and the thyristor.
7. The method of claim 1 , further comprising providing a circuit diagram for the surge protection circuit.
8. A surge protection circuit configured in accordance with the method of claim 1 .
9. A surge protection circuit for electrical equipment comprising:
a gas discharge tube (GDT) having a first breakdown voltage greater than an anticipated highest peak voltage;
a thermistor having a serial resistance of approximately 10 ohms and a second breakdown voltage greater than an impulse voltage for the GDT, wherein the impulse voltage is voltage required to excite the GDT based on the first breakdown voltage; and
a thyristor having a rated peak current greater than an anticipated peak current for the thermistor.
10. The surge protection circuit of claim 9 , wherein the thermistor has a serial resistance of approximately 10 ohms.
11. The surge protection circuit of claim 9 , wherein the thermistor is a ceramic protective temperature coefficient (CPTC) thermistor.
12. The surge protection circuit of claim 9 , wherein the thermistor is a polymer protective temperature coefficient (PPTC).
13. The surge protection circuit of claim 9 , configured to handle a surge having a 1000 V/μs impulse voltage shape.
14. An interface device comprising:
a connector to receive an input line;
circuitry configured to receive the input line; and
a surge protection circuit configured between the input line and the circuitry to protect the circuitry from external surges may be of unknown magnitude in voltage, current and energy, wherein the surge protection circuit includes
a gas discharge tube (GDT) having a first breakdown voltage greater than an anticipated highest peak voltage for the interface device;
a ceramic protective temperature coefficient (CPTC) thermistor having a second breakdown voltage greater than an impulse voltage for the GDT, and wherein the impulse voltage is voltage required to excite the GDT based on the first breakdown voltage; and
a thyristor having a rated peak current greater than an anticipated peak current for the CPTC thermistor.
15. The interface device of claim 14 , wherein the series resistance of the CPTC thermistor is approximately 10 ohms.
16. The interface device of claim 14 , wherein the circuitry is a subscriber line interface card (SLIC).
17. The interface device of claim 14 , wherein the input line is a dual wire input line, wherein the surge protection circuit includes a first GDT, a first CPTC thermistor, and a first thyristor associated with a first wire of the dual wire input line, and a second GDT, a second CPTC thermistor, and a second thyristor associated with a second wire of the dual wire input line.
18. The interface device of claim 14 , wherein the input line is a dual wire input line, and wherein the surge protection circuit includes a dual GDT having a first GDT associated with a first wire of the dual wire input line and a second GDT associated with a second wire of the dual wire input line, a first CPTC thermistor associated with the first wire and a second CPTC thermistor associated with the second wire, and a dual thyristor having a first thyristor associated with the first wire and a second thyristor associated with the second wire.
19. The interface device of claim 14 , further comprising
additional connectors to receive additional input lines; and
additional surge protection circuits configured between the additional input lines and the circuitry.
20. The interface device of claim 14 , wherein the surge protection circuit is configured to handle a surge having a 1000 V/μs impulse voltage shape.