Patent ID: 8680440

Claim:
A control circuit for controlling power to a heating element to control heat in a garment, the control circuit comprising: a power source configured to supply power to a load through a current pass element, the current pass element controlled by a control signal; a memory configured to store a discharge characteristic of the power source; a processor configured to determine a time period (T) having a time cycle beginning at Ton and a Time cycle end at Toff, where the Time cycle end is less than the time period (T), to generate the control signal each time period (T), thereby electrically connecting the power source to the load and the current pass element each time period (T); a current measuring device configured to measure an output current; and a voltage measuring device configured to measure a load voltage, wherein the processor is further configured to calculate an instantaneous power (Pi) based on the output current and the load voltage and to modify the power on time (Tontime) based on an elapsed time the garment has been operating and on the discharge characteristic and a thermal property of the garment.