Electronic digital thermostat having an improved power supply

Claim 1

A power supply circuit for providing operating power for a programmable electronic digital thermostat including a controlled semiconductor switch connected in series with an external alternating current (AC) voltage source comprising: first rectifier means coupled across said controlled semiconductor switch for rectifying said external AC voltage to produce a first direct current voltage; a transformer having a primary winding and a secondary winding, said primary winding connected in series with said controlled semiconductor switch and said external AC voltage source; second rectifier means connected across said secondary winding for rectifying the alternating current to produce a second direct current voltage; regulator means for providing a predetermined supply voltage for the programmable electronic digital thermostat; said regulator means having input means coupled to said first and second rectifier means; said first and second direct current voltages being applied to said regulator input means; and said regulator means having output means for providing said predetermined supply voltage; first inductance means connected in series and connected to said regulator input means for filtering said first and second direct current voltages; and capacitance means and second inductance means coupled in series between said regulator input means and ground potential for filtering said first and second direct current voltages.