Circuit and method for providing a constant magnetic field to actuate electromechanical relays and contactors over a large temperature range

A method for controlling a voltage applied to a coil, comprising the steps of:

• providing an adjustable voltage regulator, the voltage regulator receiving power from a source when connected thereto, the voltage regulator receiving a variable control voltage and providing a regulated voltage at an output;
• sensing a temperature of the coil with a temperature sensing device;
• coupling the regulated voltage output from the voltage regulator to a first terminal of the coil and to a first terminal of a voltage divider, the voltage divider comprised of an impedance and the temperature sensing device, the voltage divider having a midpoint at a junction of the impedance and the temperature sensing device at which a midpoint voltage is developed;
• and
• providing the midpoint voltage as the variable control voltage input to the voltage regulator;
• wherein, when the temperature of the coil changes, the resistance of the coil changes, the change in coil temperature is detected by the temperature sensing device, causing the voltage at the midpoint to change, causing the variable control voltage to change, and in turn, causing the regulated voltage at the output of the voltage regulator to change to provide a constant magnitude, temperature independent current to the coil upon the next coil actuation to assure the magnetic field will be constant for actuation without regard to the temperature of the coil.