A programmable electronic digital thermostat provides improved control of a temperature conditioning system for varying load conditions in order to maintain the ambient temperature within a predefined range of a scheduled set temperature while minimizing ambient temperature overshoots and undershoots. The thermostat includes an improved power supply circuit for simply and effectively providing its operating power utilizing an external alternating current power source of the temperature conditioning system and utilizing conventional existing wiring. The thermostat includes a microprocessor for storing a program and for performing logical control operations in accordance with the stored program and a temperature sensing circuit that provides a pulse width modulated PWM signal representative of ambient temperature in response to an enable control signal from the microprocessor, fan coil unit.
Among the important objects of the present invention are to provide an improved programmable electronic digital thermostat for controlling a temperature conditioning system for varying load conditions; to provide such thermostat utilizing actual heating and cooling history values for determining effective recovery times; to provide such thermostat enabling effective duty cycle control of the temperature conditioning system; to provide such thermostat including a power supply circuit enabling efficient, effective and reliable operation utilizing existing wiring for a conventional electromechanical thermostat; and to provide such thermostat having optimized power requirements.