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

• Current Assignee: Athena Controls, Inc. (Inductotherm Group)
• Original Assignee: Egils Evalds
• Inventors: Evalds, Egils
• Primary Examiner(s): Gilheany, Bernard A.
• Assistant Examiner(s): Bell, F. E.
• Application Number:
  US05/104,075
• Time in Patent Office: 567 Days
• Field of Search: 219/499,501 315/29SC
• US Class Current: 219/499
• CPC Class Codes: G05D 23/2401 using a heating element as a sensing element

Abstract

The present circuit employs a heating element whose electrical resistance varies in response to the heat generated thereby. The heating element comprises one leg of a bridge circuit and the output signal from the bridge circuit is connected to fire a silicon-controlled rectifier. The silicon-controlled rectifier is connected to short out a leg of the bridge circuit which is serially connected to the heating element thereby providing full power for energizing the heating element when the siliconcontrolled rectifier is turned on and simply providing control current to the heating element when the silicon-controlled rectifier is turned off.

Claims

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.

2. A temperature control circuit according to claim 1 wherein there is included a second current switching means having an input element, an output element and a control element, said input element being connected to said first circuitry means, said output element being connected to said first electrical energy input line;

second circuitry means connecting said control element of said second current switching means to said first electrical energy input line whereby a voltage is developed and stored thereby during the time when said first current switching means is conducting and characterized such that said developed voltage turns on said second current switching means during the time that said first current switching means is rendered non-conducting thereby conducting electrical current through said heating member from said second electrical energy line to said first electrical energy line.

3. A temperature control circuit according to claim 1 wherein there is further included a silicon-controlled rectifier having an input element, an output element, and a control element, said input element being connected to said first circuitry means, said output element being connected to said first electrical energy input line, and wherein there is further included a resistor connected between the input element of said first current switching means and said first electrical energy input line and wherein there is further included a capacitor connected between said input element of said first current switching means and said control element of said silicon-controlled rectifier and wherein there is further included a diode connected to conduct current between said first electrical energy input line to said capacitor to charge said capacitor whereby when said first current switching means is conducting said capacitor is charged in such a way that said silicon-controlled rectifier is biased to conduct in response to a polarity change of the electrical signal applied to said first and second electrical energy input lines.