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TEMPERATURE CONTROL CIRCUIT EMPLOYING A VARIABLE RESISTANCE HEATING ELEMENT

  • US 3,679,871 A
  • Filed: 01/05/1971
  • Issued: 07/25/1972
  • Est. Priority Date: 01/05/1971
  • Status: Expired due to Term
First Claim
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1. A temperature control circuit comprising in combination:

  • first and second electrical energy input lines;

    first voltage divider circuit means having first and second terminals respectively connected to said first and second electrical energy input lines;

    heating member means having third and fourth terminals and being capable of being electrically energized to provide heat and having an electrical resistance characteristic whIch varies with the heat being so generated, said fourth terminal being connected to said second electrical energy input line;

    first electrical resistor means having fifth and sixth terminals, said sixth terminal being connected to said third terminal of said heating member means and said fifth terminal being connected to said first electrical energy input line;

    electrical current switching means having an input element, an output element and a control element, said input element being connected to said first electrical energy input line, first circuitry means connecting said output element to said third terminal and said control element being connected to said first voltage divider circuit at a variable point between said first and second terminals, whereby when there develops a predetermined difference of potential between said control element and said output element in response to the electrical resistance developed by said heating member means, said current switching means conducts electrical current to said heating member means thereby by-passing said first electrical resistor means and whereby when there develops a lack of said predetermined difference of potential, said current switching means is non-conductive; and

    voltage phase shifting means connected between a predetermined point on said first voltage divider circuit and said variable point whereby the voltage applied to said control element is out of phase with the voltage applied to said output element so that said current switching means can be switched relatively earlier in an applied electrical energy cycle than would occur without said out of phase condition.

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