Temperature control circuit with two independent switch outputs

Claim 2

An electrical temperature control circuit energized from an alternating current voltage supply comprising: means for sensing temperature and generating a temperature signal representative thereof; means including and for time sharing said temperature sensing means by alternately generating separate setpoint temperature signals representative of two preselected setpoint temperatures during alternate and opposite phases of said alternating current supply voltage; comparator means for alternately comparing said temperature signal with each of said setpoint temperature signals during alternate and opposite phases of said alternating current supply voltage and generating an output control signal based on said comparison; two control means; and switching means responsive to said output control signal of said comparator means for alternately and selectively energizing said control means from said alternating current voltage supply.

Claim 3

A temperature control circuit as defined in claim 1 wherein said temperature sensing means comprising a bridge network including a temperature responsive resistance means.

Claim 4

A temperature control circuit as defined in claim 2 wherein said time sharing means comprises: an impedance means; and switching means responsive to like phases of said alternating current supply voltage for connecting said impedance means into said bridge network thereby selectively and alternately changing the balance point and thus the temperature setpoint of said bridge network during opposite phases of said alternating current supply voltage.

Claim 5

A temperature control circuit as defined in claim 3 wherein said impedance means comprises a resistor and said switching means comprises transistor means for connecting said resistor in parallel with one leg of said bridge network.

Claim 6

A temperature control circuit as defined in claim 1 wherein said comparator means comprises an operational amplifier arranged to compare said temperature signal and said respective setpoint temperature signals and provide a positive output control signal only when the difference between the said sensed temperature signal and the respective setpoint temperature signal is of a predetermined sign.

Claim 7

A temperature control circuit as defined in claim 5 wherein said switching means comprises an SCR, said output control signal of said comparator means being connected to the gate of said SCR, said circuit being arranged to switch and render said SCR conductive upon a positive output control signal.

Claim 8

A temperature control circuit as defined in claim 6 wherein said two control means comprise thermal relay means series connected to said alternating current voltage supply.

Claim 9

A temperature control circuit as defined in claim 7 including current blocking means permitting current conduction in each of said respective relay means only during like but opposite phases of said alternating current supply voltage and through said switching means.

Claim 10

A temperature control circuit as defined in claim 8 wherein said current blocking means comprises oppositely poled diodes series connected between said relay means, said SCR being connected between said diodes.

Claim 11

A temperature control circuit as defined in claim 1 wherein said switching means comprises an SCR connected to each of said control means, both of said SCRs being responsive to said output control signal to selectively energize said control means from said alternating current voltage supply.

Claim 12

In a self-cleaning oven having a heating element for supplying heat during both baking and cleaning and an oven door locking mechanism normally locked only during cleaning, a temperature control circuit as defined in claim 7 wherein one of said thermal relays controls said heating element and the other thermal relay controls said door locking mechanism.

Claim 13

The invention as defined in claim 11 wherein said temperature setpoint signals represent the maximum cleaning and baking temperatures of said oven.

Claim 14

A temperature control circuit as defined in claim 2 wherein said bridge network including said temperature responsive resistance is balanced at a third low temperature point representative of a temperature value below the lowest value of temperature to be sensed by said temperature responsive resistance means; and said time sharing means comprises two impedances and switching means responsive to opposite phases of said alternating current supply voltage for alternately connecting one of said respective two impedances into said bridge network thereby selectively and alternately changing the bridge network balance point and thus the temperature setpoint between a first and second setpoint value, a period being allowed between each setpoint signal during which time, neither impedance is switched in bridge so that the bridge balances at its third low temperature balance point, both of said temperature setpoint values being within the range of temperatures to be sensed by said temperature responsive resistance means, said circuit being arranged to apply a positive going output control signal to said switching means only when said temperature signal is greater than said third temperature balance point and less than a selected one of first and second setpoint values.

Claim 15

A temperature control circuit as defined in claim 13 including capacitor means interconnecting said comparator means and said switching means wherein said switching means is rendered conductive only on positive going transitions of said output control signal.

Claim 16

A temperature control circuit as defined in claim 14 wherein said alternating current voltage supply is from the secondary winding of a stepdown transformer energized by an alternating current line voltage.

Claim 17

A temperature control circuit as defined in claim 15 wherein said control means are directly energized by said switching means from an alternating current line voltage.