Circuit for determining and controlling the current supplied to an adjustable resistance load

Claim 1

A circuit for determining and controlling the electrical current supplied to an adjustable resistance load comprising in combination: a source of pulsating direct current signals; bridge circuit means having first and second input terminal sides, first circuitry means connecting said source of pulsating direct current signals to said first input terminal side; second circuitry means connecting said second input terminal side to said source of pulsating direct current signals; said bridge circuit means having temperature responsive resistor means as a first leg, first adjustable resistor means forming second and third legs and havIng an adjustable tap thereon as a first output terminal means of said bridge, second resistor means forming a fourth leg; second output terminal means connecting said fourth leg to said first leg; first current switching means having an input element, an output element, and a control element; said input element connected to said first output terminal, said control element connected to said second output terminal; first current path means having an input terminal and an output terminal, said input terminal connected to said output element of said first current switching means, said output terminal connected to said second circuitry means; voltage developing means having first and second terminals, said second terminal connected to said second circuitry means; second current path means connected between said input terminal of said first current path means and said first terminal of said voltage developing means whereby the voltage appearing at said first terminal of said first current path means follows the voltage developed at said voltage developing means, said second current path means including a second adjustable resistor to vary the voltage developed at said voltage developing means in accordance with an adjustment thereof; second current switching means having an input element, an output element and a control element, said control element connected to said first terminal of said voltage developing means, said input element connected to said second terminal of said first current path means, said output element connected to said second circuitry means whereby the voltage appearing at said input element follows the voltage appearing at said first terminal of said first current path means when said last mentioned voltage exceeds the voltage otherwise developed across said input and output elements of said second current switching means; said second current switching means having the capacity to be rendered conducting when the voltage developed by said voltage developing means exceeds a particular percentage of the voltage appearing across said input and output elements of said second current switching means; and load current switching means adapted to be connected to a source of electrical current and adapted to be connected to a load, said load current switching means coupled to be turned on in response to current conduction through said second current switching means.