Temperature sensing circuit with high noise immunity

In a refrigerator system having refrigeration apparatus for cooling a refrigerated compartment and a temperature responsive refrigerator control exterior of the refrigerated compartment, a temperature sensing circuit with improved immunity to noise occurring in the refrigerator system, comprising:

• a circuit board for the temperature sensing circuit located within the refrigerated compartment;
• an analog temperature sensing device mounted in the refrigerated compartment and connected to the circuit board for coupling a low level analog sensing signal to the temperature sensing circuit;
• a trigger circuit on the circuit board for generating a digital output as the temperature sensed by the analog device varies above or below a set point including a pair of cascaded comparison stages with the first stage coupled to the analog temperature sensing device and having substantially no hysteresis in its response and the second comparison stage having substantial hysteresis in its response to produce the digital output;
• and
• a housing for the refrigerator control located external to the refrigerated compartment, and a wire connecting the circuit board to the external housing for coupling the digital output to the refirgerator control therein.

In a refrigerator system having refrigeration apparatus for cooling a refrigerated compartment, a temperature sensing circuit with improved immunity to noise occurring in the refrigerator system, comprising:

• a circuit board for the temperature sensing circuit located within the refrigerated compartment;
• an analog temperature sensing device mounted in the refrigerated compartment and connected to the circuit board for coupling a low level analog sensing signal to the temperature sensing circuit;
• and
• a trigger circuit on the circuit board for generating a digital output as the temperature sensed by the analog device varies above or below a set point, wherein the trigger circuit includes a pair of cascaded comparison stages with the first stage coupled to the analog temperature sensing device and having substantially no hysteresis in its response and the second comparison stage having substantial hysteresis in its response to produce the digital output.