Transformer and control units for ac control

Details Transformer and control units for ac control Transformer and control units for ac control

2000-11-24

2002-08-06

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Polyphase a.c. supply

Transformer in the supply circuit

C315S276000, C315S288000, C315S360000, C323S355000, C336S220000, C361S622000, C361S623000

Reexamination Certificate

active

06429598

ABSTRACT:

This invention relates to transformer and control units for ac (alternating current) control.
BACKGROUND OF THE INVENTION
There is a variety of known units which can be plugged into a conventional ac outlet to provide a source of controlled or modified power to a device connected thereto. Among these units are time switches, lamp dimmers, PLC (power line carrier) units which for example operate in accordance with the X-10 protocol, and transformer units which provide a relatively low voltage ac or dc supply for numerous types of electronic device. These units may be in the form of wall units with prongs which plug directly into an ac outlet, or in the form of floor or desk units with a supply cable having a plug which is plugged into an ac outlet. The term “plugged” as used herein is intended to embrace all forms of electrical connection to ac outlets, including for example screw-threaded and bayonet connections typically provided for lamps. The term “ac outlet” as used herein is intended to embrace both grounded (e.g. two-pin) and ungrounded (e.g. three-pin) outlets of any form, and includes an ac outlet provided at the end of a connection cable. The term “transformer unit” as used herein is intended to embrace both wall transformer units and floor or desk transformer units.
A time switch provides timed control for supply of ac power to an ac outlet on the time switch, or to an ac power output cable of the time switch. A lamp dimmer similarly provides controlled power to an ac outlet on the lamp dimmer unit or to a power output cable to which a lamp can be connected. The lamp dimmer provides for example a manual control of the conduction phase angle of a triac during each half cycle of the ac waveform, thereby controlling the brightness of the lamp. PLC units provide similar functions but can be remotely controlled, by commands sent by a PLC control unit via the ac power supply lines, to provide timed control and/or dimming control functions.
An X-10 PLC control unit (Radio Shack Home Control Center Computer Interface, Catalog No. 61-2417) is known which has prongs to plug it into an ac outlet, an ac outlet which is directly connected to the prongs, and a modular telephone cord connector providing an interface for connection to a computer. Within this unit, a transformer is connected to the prongs to supply low voltage power to PLC circuits of the unit. Software running on a connected computer enables PLC commands, including commands for timing and dimming functions, to be downloaded to the control unit, which subsequently sends these commands via the ac power lines without requiring continued connection or operation of the computer.
Transformer units which provide relatively low voltage supplies for electronic devices include numerous units for providing various individual or combinations of ac, unregulated dc, or regulated dc voltages at various currents and via various types of connector.
Every day, millions of people are awakened from sleep by a sudden noise, loud enough to wake the sleeper, from an alarm clock, clock radio, or similar device. It has been recognized that such a disruptive start to each day is undesirable, and that a more natural waking environment can be provided by a gradual increase in light, simulating dawn. Accordingly, various dawn/dusk simulators are known and for example are available from The SunBox® Co. (www.sunboxco.com) of Gaithersburg, Md. These units combine an analog or digital clock with a lamp, or an ac outlet for a lamp, whose brightness is controlled, the lamp being brightened at a desired time to simulate dawn or being dimmed at another desired time to simulate dusk. One of these units further provides sounds that get louder through a simulated dawn and quieter through a simulated dusk, as well as a conventional alarm sound. A disadvantage of such units is their relatively high cost, which makes them impractical for the vast majority of people, especially if such a unit is to be provided in each bedroom of a residence.
It is desirable, therefore, to provide a dawn simulator at a relatively low cost.
It can be appreciated that a dawn simulator comprises a timer, an automatically controlled lamp dimmer, and a lamp. Timers in the form of 24-hour time switches as discussed above are readily available at very low cost, and bedside plug-in lamps already exist in most bedrooms or are also easily provided. However, providing an automatically controlled lamp dimmer at low cost presents a more significant difficulty. For simulating dawn and waking a sleeper naturally, it is preferable for a lamp to be relatively close to the sleeper to provide an ultimately bright source of light, and it is necessary for the lamp to be turned on initially at a very low light level, and to be brightened smoothly over a period of time. Most common lamp dimmers do not allow a lamp to be turned on initially at a very dim level, and are not automatically controlled.
Using a PLC lamp module and a series of successive PLC commands over a period of time, it is possible to brighten a lamp from a dim level to a full brightness level in, for example, 16 brightness steps. However, the most commonly available PLC lamp modules do not permit the lamp to be initially turned on at anything other than its full brightness level, which is as disruptive to a sleeper as the sudden sound of an alarm clock. Although PLC lamp modules exist which obviate this problem, they are less readily available and are more costly. In any event, this solution also requires a PLC control unit, for example as discussed above, to issue the required series of PLC commands, as well as a computer from which to download the series of commands to the PLC control unit and the knowledge to set up, operate, and maintain this.
A need exists, therefore, for an effective dawn simulator that can be provided at low cost, and that does not require relatively sophisticated equipment and knowledge for its proper operation.
It is known that a low-cost microcontroller can be used to provide a lamp dimmer. For example, “PICDIM Lamp Dimmer for the PIC12C508”, having a copyright date of 1997 and available from the web site (www.microchip.com) of Microchip Technology Inc. of Chandler, Ariz., where it is identified as PICREF-4, describes the use of a PlCmicro® 8-bit microcontroller to provide zero crossing detection of an ac waveform and control of the conduction phase angle of a triac to provide manually controlled lamp dimming. Other documents on the same web site provide extensive further information on such microcontrollers and their applications, including for timing functions.
Microcontroller circuits typically have very small power requirements which are often met by using a transformerless ac power supply, an example of which is a capacitive power supply of the type shown in the PICREF-4 document. That document properly draws prominent attention to potential hazards of transformerless power supplies, namely that they present a potential risk because (especially with incorrect ac supply wiring or a malfunction) any part of the connected circuit may be at an ac supply voltage, and there is no transformer isolation for transients between the ac supply and the powered circuit. These potential hazards become of increasing significance in a lamp dimmer with manual switches which may be operated by a person who is not fully awake, and where transients are likely to be produced by the switching of the triac in each half cycle of the ac waveform. Although other protection measures are known for transformerless power supplies, these add complexity without fully avoiding all of the potential hazards. Thus the isolation advantages of a transformer power supply over-ride its disadvantages of bulk and cost, these disadvantages being of relatively low consequence in view of the low power requirements of a microcontroller.
SUMMARY OF THE INVENTION
The invention is concerned with addressing the need discussed above in a manner that facilitates providing a safe, versatile, practical, and economic solution.
According to one aspect, thi

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