High sensitivity diode temperature sensor with adjustable current source

• US 6,342,997 B1
• Filed: 04/26/2000
• Issued: 01/29/2002
• Est. Priority Date: 02/11/1998
• Status: Expired due to Fees

• Current Assignee: Therm-O-Disc Incorporated (Emerson Electric Company)
• Original Assignee: Therm-O-Disc Incorporated (Emerson Electric Company)
• Inventors: Anderson, Thomas C., Tennant, James A., Zimmerman, Bernd D., Khadkikar, Prasad S., Reynolds, David W.
• Primary Examiner(s): HUYNH, KIM NGOC
• Application Number:
  US09/558,918
• Time in Patent Office: 643 Days
• Field of Search: 361/103, 361/106, 361/100, 361/93.8, 307/116, 307/117, 307/127, 307/126, 219/502, 219/482, 219/494, 219/490, 257/467, 257/414
• US Class Current: 361/103
• CPC Class Codes: G01K 3/005 Circuits arrangements for indicating a predetermined temperature fire detection G08B17/00
• CPC Class Codes: G01K 7/01 using semiconducting elements having PN junctions G01K7/02, G01K7/16, G01K7/30 take precedence

Abstract

A temperature control circuit provides for optical isolation, dry start protection, dedicated load control, manual reset, and relay control in hot water heaters and related applications. The control circuit removes power from a load at a first temperature, and includes a first optical isolation device, a first diode temperature sensor, and a first switching mechanism. The first optical isolation device controls operation of a power source, where the power source is provided to the load, such as a hot water heater heating element. The first diode temperature sensor is biased to provide a switching signal at the first temperature. The first switching mechanism is disposed between the first diode temperature sensor and the first optical isolation device, where the first switching mechanism disengages operation of the first optical isolation device in response to the switching signal. The control circuit can further include a high limit cycling circuit for disengaging operation of the power source at the second temperature. A latching circuit can be used to maintain the temperature control circuit in a switched state until a manual reset occurs.

Claims

1. A temperature control circuit for removing power from a load at a first temperature, comprising:

a first optical isolation device selectively connecting a power source to the load, the power source providing power to the load;

a first diode temperature sensor having a first reverse-biased Schottky diode and a first adjustable constant current source coupled to the first diode for applying an adjustable reverse leakage current to the first diode, wherein a voltage drop across the first reverse-biased diode corresponds to a sensed temperature, the sensor biased to provide a switching signal at the first temperature; and

a first switching mechanism disposed between the first diode temperature sensor and the first optical isolation device, the first switching mechanism disengaging operation of the first optical isolation device in response to the switching signal.

2. The temperature control circuit of claim 1 wherein the first switching mechanism is shunted across the first optical isolation device.

3. The temperature control circuit of claim 1 wherein the first switching mechanism is connected in series with the first optical isolation device.

4. The temperature control circuit of claim 1 wherein the first optical isolation device is a photo-triac driver.

5. The temperature control circuit of claim 1 further including a high limit cycling circuit for disengaging operation of the power source at a second temperature.

6. The temperature control circuit of claim 5 wherein the high limit cycling circuit includes:

a second diode temperature sensor having a second reverse-biased Schottky diode and a second adjustable constant current source coupled to the second diode for applying an adjustable reverse leakage current to the second diode, wherein a voltage drop across the second reverse-biased diode corresponds to a sensed temperature, the sensor biased to provide a switching signal at the second temperature; and

a second switching mechanism coupled to the first optical isolation device, the second switching mechanism disengaging operation of the first optical isolation device in response to the switching signal.

7. The temperature control circuit of claim 5 wherein the high limit cycling circuit includes:

a second optical isolation device controlling operation of the power source, the second optical isolation device connected in series with the first optical isolation device;

a second diode temperature sensor having a second reverse-biased Schottky diode and a second adjustable constant current source coupled to the second diode for applying an adjustable reverse leakage current to the second diode, wherein a voltage drop across the second reverse-biased diode corresponds to a sensed temperature, the sensor biased to provide a switching signal at the second temperature; and

a second switching mechanism coupled to the second optical isolation device, the second switching mechanism disengaging operation of the second optical isolation device in response to the switching signal.

8. The temperature control circuit of claim 1 further including a latching circuit disposed between the first switching mechanism and a second optical isolation device, the latching circuit maintaining the temperature control circuit in a switched state until a manual reset occurs.

9. The temperature control circuit of claim 8 wherein the latching circuit includes:

a silicon controlled rectifier shunted across the second optical isolation device; and

a manual reset switch connected in series with the second optical isolation device.

10. The temperature control circuit of claim 8 wherein the latching circuit includes:

a bipolar transistor shunted across the second optical isolation device;

a silicon controlled rectifier connected in series with the bipolar transistor; and

a manual reset switch connected in series with the second optical isolation device.

11. The temperature control circuit of claim 1 further including a latching circuit disposed between the first switching mechanism and the first optical isolation device, the latching circuit maintaining the temperature control circuit in a switched state until a manual reset occurs.

12. The temperature control circuit of claim 1 wherein the latching circuit includes:

a silicon controlled rectifier shunted across the first optical isolation device; and

a manual reset switch connected in series with the first optical isolation device.

13. The temperature control circuit of claim 1 wherein the latching circuit includes:

a bipolar transistor shunted across the first optical isolation device;

a silicon controlled rectifier connected in series with the bipolar transistor; and

a manual reset switch connected in series with the first optical isolation device.

14. The temperature control circuit of claim 1 further including a level-based protection circuit for disengaging the power source at a predetermined fluid level.

15. The temperature control circuit of claim 14 wherein the protection circuit includes a reed switch.

16. A temperature control circuit for removing power from a load at a first temperature, comprising:

a first optical isolation device selectively connecting a power source to the load, the power source providing power to the load;

a first diode temperature sensor having a first reverse-biased diode and a first adjustable constant voltage source for applying an adjustable reverse voltage to the first diode;

wherein a reverse current through the first reverse-biased diode corresponds to a sensed temperature, the sensor biased to provide a switching signal at the first temperature; and

a first switching mechanism disposed between the first diode temperature sensor and the first optical isolation device, the first switching mechanism disengaging operation of the first optical isolation device in response to the switching signal.

17. The temperature control circuit of claim 16 further including a high limit cycling circuit for disengaging operation of the power source at a second temperature.

18. A relay driver circuit comprising:

a relay coil circuit coupled to a power source, the power source providing power to a load;

a diode temperature sensor having a reverse-biased Schottky diode and an adjustable constant current source coupled to the reverse-biased diode for applying an adjustable reverse leakage current to the reverse-biased diode, wherein a voltage drop across the reverse-biased diode corresponds to a sensed temperature, the sensor biased to provide a switching signal at a sensing temperature; and

a switching mechanism coupled to the relay coil circuit, the switching mechanism controlling the relay coil circuit in response to the switching signal.

19. The relay driver circuit of claim 18 wherein the switching mechanism is a field effect transistor.

20. The relay driver circuit of claim 18 wherein the relay coil circuit includes a Schmitt trigger circuit for eliminating chatter.

21. A method for removing power from a load at a first temperature, the method comprising the steps of:

selectively connecting a power source to the load with a first optical isolation device;

coupling an adjustable constant current source to a reverse biased Schottky diode such that a first diode temperature sensor is biased to provide a switching signal at the first temperature, the adjustable constant current source applying an adjustable leakage current to the diode, wherein a voltage drop across the reverse-biased diode corresponds to a sensed temperature; and

disengaging operation of the first optical isolation device in response to the switching signal.

22. The method of claim 21 further including the step of disengaging operation of the power source at a second temperature.