Electronic digital thermostat having an improved power supply

• US 4,948,044 A
• Filed: 08/21/1989
• Issued: 08/14/1990
• Est. Priority Date: 08/21/1989
• Status: Expired due to Fees

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Harper-Wyman Company
• Inventors: Cacciatore, Joseph J.
• Primary Examiner(s): Wayner, William E.
• Application Number:
  US07/396,522
• Time in Patent Office: 358 Days
• Field of Search: 236/46 R, 165/12
• US Class Current: 236/46.00R
• CPC Class Codes: G05D 23/1904 variable in time
• CPC Class Codes: H02J 9/061 for DC powered loads

Abstract

An improved power supply circuit is provided for use with programmable electronic digital thermostats of the type including a controlled semiconductor switch connected in series with an external alternating current (AC) voltage source. The power supply circuit includes a first rectifier bridge coupled across the controlled semiconductor switch for rectifying the external AC voltage to produce a first direct current voltage. A transformer has a primary winding and a secondary winding. The primary winding is connected in series with the controlled semiconductor switch and the external AC voltage source. A second rectifier bridge is connected across the secondary winding for rectifying the alternating current to produce a second direct current voltage. A voltage regulator has an input coupled to the first and second rectifier bridges and an output for providing a predetermined supply voltage for the programmable electronic digital thermostat.

Claims

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.

2. A power supply circuit as recited in claim 1 further comprising a battery coupled to said regulator input means for providing a backup battery voltage responsive to said first and said second direct current voltages below said battery voltage.

3. A power supply circuit as recited in claim 1 wherein said primary winding of said transformer has a low impedance value whereby a small voltage drop across said primary winding results when the controlled semiconductor switch is activated.

4. A power supply circuit as recited in claim 3 wherein said secondary winding provides a step-up voltage potential whereby to enable said regulator output means for providing said predetermined supply voltage.

5. A power supply circuit as recited in claim 1 wherein said transformer has a step-up ratio of approximately 16:

1 between said secondary winding and said primary winding.

6. A power supply circuit as recited in claim 1 wherein said regulator means is an integrated circuit device.