Electricity: power supply or regulation systems – External or operator controlled
Patent
1997-04-11
1998-09-22
Hecker, Stuart N.
Electricity: power supply or regulation systems
External or operator controlled
323905, G05B 2402, G05F 110, H02J 100
Patent
active
058119639
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to power supplies such as may be used to provide DC power from AC sources, and more particularly to the provision of a control voltage for a switchable series load control device.
2. Description of the Prior Art
Conventional residential and commercial AC wiring for lighting, heating and air conditioning provides a series connection in a wall mounted switch box for controlling the application of the AC mains power to the load. A series load control device, such as a simple hand operated mechanical switch, a relay control switch or a room occupancy detector, is positioned in the switch box to control the power applied from the AC mains to the load by making or breaking the series connection.
The hot side of the AC mains, called the AC hot line, is usually connected directly to the switch box together with the so-called switch leg from the load. One end of the load, such as a bank of room lights, is connected outside of the switch box directly to the neutral side of the AC mains. The other side of the load is called the switch leg and is made available in the switch box. Depending upon the application, an earth ground connection may also be made available at the switch box.
In operation, AC power is applied from the AC mains to the load when the series connection is made in the switch box between the switch leg and the AC hot line. This may be called the "lights-on" power condition although the load may be something other than lights, such as heating or cooling systems or the like. AC power is not applied to the load when the series connection in the switch box is not made. This is called the "lights-off" power condition.
Many simple series load control devices such as a mechanical room wall switch operate conveniently without the use of applied power other than the AC power applied to the load. As such series load control devices become more sophisticated, a separate source of power for powering the series load control device itself is often required in addition to the AC mains power applied to the load. For example, when a wall mounted room occupancy detector is used to control the lights in a room, the occupancy detector itself requires power from a control circuit voltage source for its control circuitry such as the occupancy detector transmitter, receiver and control relay. Control circuit voltage is typically DC voltage derived by rectification and regulation from the AC mains.
It is extremely convenient, when installing a series load control device in a wall mounted switch box, to derive the control circuit voltage directly from the existing wiring of the switch box rather than by leading additional wires to the switch box. During the lights-off power condition, control circuit voltage is most often derived by rectifying and regulating the AC voltage available between the AC hot and switch legs applied to the switch box. The development of this supply results in a small amount of current to flow through the AC load known as "leakage current". The amount of leakage current varies depending on factors including the AC voltage, load size and type, and control circuit requirements. Circuits are typically designed to provide sufficient "leakage current" for a worst case operating condition, and accepting waste at all other operating conditions. As load technology improves, specifically in the area of electronic lighting ballasts, AC loads are becoming less tolerant of excess leakage current.
During the lights-on condition, the AC hot and switch legs are series connected to each other, so another source of power from which the control circuit voltage may be derived must be employed.
Conventional designs provide control circuit voltage during the lights-on power condition from a circuit component placed in series with the load. One such series circuit component is a transformer winding as shown for example in U.S. Pat. No. 4,713,598 (Smith). Such conventional designs, however, waste substantial amounts of power and are oft
REFERENCES:
patent: 4270058 (1981-05-01), Schornack
patent: 4300090 (1981-11-01), Weber
patent: 4754213 (1988-06-01), Dubot et al.
patent: 4878010 (1989-10-01), Weber
Hecker Stuart N.
May John M.
Novitas Incorporated
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