THYRISTOR CIRCUIT PROVIDING OVERCURRENT PROTECTION TO A LOW IMPEDANCE LOAD

• US 20040212939A1
• Filed: 04/23/2003
• Published: 10/28/2004
• Est. Priority Date: 04/23/2003
• Status: Active Grant

• Current Assignee: Teccor Electronics Incorporated (Teccor)
• Original Assignee: Teccor Electronics Incorporated (Teccor)
• Inventors: Casey, Kelly C.
• Granted Patent: US 6,862,162 B2
• Time in Patent Office: Days
• US Class Current: 361/57
• CPC Class Codes: H01L 29/7408 the device being a capacitor or a resistor
• CPC Class Codes: H01L 29/747 Bidirectional devices, e.g. triacs
• CPC Class Codes: H02H 9/041 using a short-circuiting device

Abstract

A thyristor provides overcurrent protection to a low impedance load, such as a transformer, by adding a resistance in series with the transformer winding. As overcurrents attempt to pass through the transformer winding, a sufficient voltage is generated in the transformer so that a thyristor connected thereacross is triggered into conduction. A resistance formed between the thyristor gate and cathode establishes the threshold of current that can pass through the transformer winding before the thyristor is triggered. When triggered into conduction, the thyristor shunts the current and the transformer is thus protected.

Claims

1. A thyristor circuit for use with a low impedance load, comprising:

a gated thyristor having an anode, a cathode and a gate;

a loading impedance for connection in series with said low impedance load;

said anode and gate of said gated thyristor adapted for connection in parallel across said low impedance load and said loading impedance; and

said anode and said cathode forming terminals for said thyristor circuit, whereby when a current exceeding a predefined magnitude passes through said low impedance load, said gated thyristor is gated on and current is shunted around said low impedance load.

2. The thyristor circuit of claim 1, further including a resistor coupled between said gate and cathode of said gated thyristor, said resistor functioning to provide a voltage across a gate-cathode junction of said gated thyristor.

3. The thyristor circuit of claim 1, wherein said gated thyristor comprises a triac.

4. The thyristor circuit of claim 1, wherein said low impedance load comprises a transformer winding.

5. The thyristor circuit of claim 1, wherein said gated thyristor comprises an SCR.

6. The thyristor circuit of claim 1, wherein said loading impedance comprises a resistor.

7. The thyristor circuit of claim 6, wherein said resistor comprises a discrete resistor component.

8. The thyristor circuit of claim 1, wherein said loading impedance is formed in semiconductor material with said gated thyristor.

9. The thyristor circuit of claim 1, wherein said gated thyristor is constructed such that an overvoltage applied across said cathode and anode triggers said gated thyristor on to protect said low impedance load from sustained voltages exceeding a predefined threshold.

10. The thyristor circuit of claim 1, wherein said loading impedance functions to increase the impedance coupled across said gated thyristor.

11. The thyristor circuit of claim 1, further including a rectifier coupled across the anode and cathode of said gated thyristor, said rectifier functioning to shunt current of a specified polarity around said low impedance load.

12. The thyristor circuit of claim 1, wherein said gated thyristor device is constructed to respond to an overvoltage exceeding a threshold, where said overvoltage is coupled between the cathode and anode.

13. The thyristor circuit of claim 1, further including in combination the low impedance load.

14. A thyristor circuit for use with a transformer load, comprising:

a first resistor adapted for connection in series with said transformer load to provide an additional resistance external to said transformer load;

a gated thyristor having an anode, cathode and gate, said anode and said gate adapted for connection in parallel across said first resistor and the transformer load; and

a second resistor connected between said gate and cathode of said gated thyristor, said second resistor functioning to establish an overcurrent threshold for said thyristor circuit, whereby said gated thyristor is triggered into conduction when said overcurrent threshold is exceeded to thereby prevent the overcurrent from passing through the transformer load.

15. The thyristor circuit of claim 14, wherein said first and said second resistors are integrally formed in semiconductor material with said gated thyristor.

16. The thyristor circuit of claim 15, wherein said first resistor is formed from one surface of a semiconductor chip to an opposite surface thereof.

17. The thyristor circuit of claim 14, further including in combination a telephone line having one conductor coupled to a fuse, and said fuse connected to the transformer load, and a second conductor of said telephone line coupled to the cathode of said gated thyristor.

18. The thyristor circuit of claim 14, wherein said first resistor has a resistance in the range of about 1-5 ohms.

19. The thyristor circuit of claim 14, wherein said gated thyristor is constructed to respond to an overvoltage exceeding a predefined magnitude coupled between the cathode and anode.

20. A thyristor circuit for use with a transformer defining a load, comprising:

said transformer packaged as a modular component, said transformer having a first winding inductively coupled to a second winding;

a first resistor connected in series with the first winding of said transformer to provide an additional resistance to said first winding, said first resistor packaged with said transformer so as to be a unitary modular component;

a gated thyristor having an anode, cathode and gate, said anode and said gate adapted for connection in parallel across said first resistor and said first winding; and

a second resistor connected between said gate and said cathode of said gated thyristor, said second resistor functioning to establish an overcurrent threshold for said thyristor circuit, whereby said gated thyristor is triggered into conduction when said overcurrent threshold is exceeded to thereby prevent the overcurrent from passing through the transformer load.

21. The thyristor circuit of claim 20, wherein said first resistor comprises a discrete resistor.

22. The thyristor circuit of claim 20, wherein said first resistor comprises a resistance formed in a wire forming the first winding.

23. A method of using a gated thyristor to protect a low impedance load from overcurrent conditions, comprising the steps of:

coupling an anode terminal and a gate terminal of a gated thyristor across the low impedance load;

adding a resistance in series with the low impedance load to increase a composite impedance thereof;

causing the gated thyristor to be driven to a latched state when a current exceeding a threshold attempts to pass through the low impedance load; and

causing the current exceeding said threshold to be coupled through the gated thyristor between the anode terminal and a cathode terminal of the gated thyristor, thereby routing the current around the low impedance load.

24. The method of claim 23, further including using a thyristor having a resistance incorporated therein, and adding the resistance in series with the low impedance load by connecting the thyristor across the low impedance load.

25. The method of claim 23, further including using a bias resistance between the gate terminal and the cathode terminal to establish said threshold.

26. The method of claim 25, further including using a bias resistance incorporated in said gated thyristor.