Power supply for electronic thermostat

Details Power supply for electronic thermostat Power supply for electronic thermostat

1999-07-28

2001-03-20

Wong, Peter S. (Department: 2838)

Electric power conversion systems

Current conversion

With condition responsive means to control the output...

C315S160000

Reexamination Certificate

active

06205041

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to wall mounted electronic thermostats and, in particular, to power supplies for such thermostats.
Wall mounted electronic thermostats for controlling temperatures in rooms are well known. These devices are commonly powered by batteries or by low voltage alternating current sources, typically 24 volts AC. The 24 volt AC power must be reduced to a lower level DC voltage for use in supplying power to the various component parts of the thermostat. This has heretofore been accomplished by various power supply circuits, which employ resistors to reduce the voltage level. These voltage dropping resistors dissipate heat which in turn can impact the sensing of room temperature by the thermostat. These resistors also produce additional loads on the transformer, which provides the stepped down 24 volts AC to the thermostat.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an electronic thermostat with a power supply circuit that substantially reduces the amount of heat produced by the power supply circuit in stepping down the voltage through the voltage dropping resistors.
The above and other objects are achieved by a power supply circuit, which includes a half wave rectification of the 24 volt AC signal. Resistors downstream of the half wave rectification significantly drop the voltage of the half wave signal. In accordance with the invention, a gated rectifier is located downstream of the voltage dropping resistors. The gated rectifier is preferably a silicon controlled rectifier. The silicon controlled rectifier is operative to conduct only when the output voltage from the silicon controlled rectifier drops below a voltage at the gate of the silicon controlled rectifier. The voltage at the gate of the silicon controlled rectifier is defined by certain gating circuitry. The current flowing through the silicon controlled rectifier when it is conducting preferably charges a capacitor connected to the output of the silicon controlled rectifier. The voltage preferably defined by the capacitor at the output of the silicon controlled rectifier is the voltage that is applied to the various elements of the electronic thermostat. The current flowing through the voltage dropping resistors drops off when the silicon controlled rectifier does not conduct. This eliminates the dissipation of heat in these resistors that would otherwise occur if current were constantly flowing through the silicon controlled rectifier.


REFERENCES:
patent: 3585444 (1971-06-01), Crowley
patent: 4456871 (1984-06-01), Stich
patent: 4632303 (1986-12-01), Rodittis
patent: 4775100 (1988-10-01), Gouldey et al.
patent: 4776514 (1988-10-01), Johnstone et al.
patent: 4948044 (1990-08-01), Cacciatore
patent: 5467921 (1995-11-01), Shreeve et al.
patent: 5687068 (1997-11-01), Jamieson et al.

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