Method and apparatus for preventing cooktop fires

1. A power circuit for a cooking appliance, the power circuit comprising:

an electric heating element; and

a thermal switch assembly in series with the electric heating element, the thermal switch assembly including:

a first contact connected to the electric heating element,

a second contact, and

a bimetal element configured to electrically connect and disconnect the first and second contacts,

the bimetal element establishing an electrical connection between the first contact and the second contact when a temperature of the bimetal element, as influenced by the electric heating element, is below a predetermined cut-off temperature, and the bimetal element no longer electrically connecting the first contact and the second contact when the temperature of the bimetal element, as influenced by the electric heating element, is at or above the predetermined cut-off temperature, and

a first voltage being applied to the electric heating element when the bimetal element electrically connects the first contact and the second contact and a second voltage, lower than the first voltage, is applied to the electric heating element when the bimetal element electrically disconnects the first contact and the second contact,

wherein the bimetal element is connected in series with the electric heating element.

2. The power circuit according to claim 1 , the predetermined cut-off temperature corresponding to the electric heating element being less than or equal to about 400° C.

3. The power circuit according to claim 1 , the predetermined cut-off temperature corresponding to the electric heating element being less than a maximum-operable-temperature of the heating element.

4. The power circuit according to claim 1 , the thermal switch assembly further comprising:

a diode connected to the first contact and the second contact via a bypass around the bimetal element effective to supply half-waveform power to the electric heating element when the bimetal element no longer electrically connects the first contact and the second contact.

5. The power circuit according to claim 1 , the second contact being connected to a phase conductor at a first voltage, the thermal switch assembly further comprising:

a third contact connected to a conductor at a second voltage lower than the first voltage,

the bimetal element electrically connecting the first contact to the third contact when the bimetal element, as influenced by the electric heating element, is at or above the predetermined cut-off temperature, to thereby apply the second voltage to the electric heating element.

6. A power circuit for controlling power to a heating element of a cooking appliance, the power circuit comprising:

an electric heating element; and

a thermal switch assembly in series with the electric heating element, the thermal switch assembly including:

a first contact connected to the electric heating element,

a second contact,

a bimetal element configured to electrically connect and disconnect the first and second contacts based on a temperature of the bimetal element,

a bypass connected to the first contact and the second contact for bypassing the bimetal element, and

a diode disposed in the bypass,

the bimetal element establishing an electrical connection between the first contact and the second contact when a temperature of the bimetal element is below a predetermined cut-off temperature, and the bimetal element no longer electrically connecting the first contact and the second contact when the bimetal element is at or above the predetermined cut-off temperature.

7. The power circuit according to claim 6 , the predetermined cut-off temperature corresponding to the electric heating element being less than or equal to about 400° C.

8. The power circuit according to claim 6 , the predetermined cut-off temperature corresponding to the electric heating element being less than a maximum-operable-temperature of the heating element.

9. A power circuit for a cooking appliance, the power circuit comprising:

an electric heating element; and

a thermal switch assembly in series with the electric heating element, the thermal switch assembly including:

a first contact connected to the electric heating element,

a second contact connected to a phase conductor at a first voltage,

a third contact connected to a conductor at a second voltage lower than the first voltage, and

a bimetal element configured to alternately connect and disconnect the first contact to and from each of the second contact and the third contact,

the bimetal element establishing an electrical connection between the first contact and the second contact when a temperature of the bimetal element is below a predetermined cut-off temperature, and the bimetal element establishing an electrical connection between the first contact and the third contact when the bimetal element is at or above the predetermined cut-off temperature,

wherein the bimetal element is connected in series with the electric heating element.

10. The power circuit according to claim 9 , the predetermined cut-off temperature corresponding to the electric heating element being less than or equal to about 400° C.

11. The power circuit according to claim 9 , the predetermined cut-off temperature corresponding to the electric heating element being less than a maximum-operable-temperature of the heating element.

12. A method for operating an electric heating element of a cooking appliance having a bimetal element in series with the electric heating element, comprising:

supplying a full-waveform power to the heating element when the bimetal element is below a predetermined cut-off temperature, and

supplying a half-waveform power when the bimetal element is at or above said predetermined cut-off temperature.

13. The method according to claim 12 , the step of supplying the half-waveform power including passing current through a diode connected in parallel with the bimetal element.

14. The method according to claim 12 , wherein the half-waveform power is rectified.