Electrical transmission or interconnection systems – Switching systems – Switch actuation
Reexamination Certificate
2002-03-22
2004-11-16
Toatley, Jr., Gregory J. (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
Switch actuation
Reexamination Certificate
active
06819014
ABSTRACT:
FIELD OF INVENTION
The present invention relates to electrical power switches and, more particularly, to electrical power switches including line-powered switching control means. More specifically, this invention relates to a remote controllable two-terminal AC electrical power switch including a line-powered switching control means. Yet more specifically, although not solely limiting thereto, this invention also relates to retro-fittable two-terminal wall-mountable power switch including line-powered remote-controllable switching control means. This invention also relates to circuit arrangements for switching on and off an electrical load by line-powered automated switching control means.
BACKGROUND OF THE INVENTION
An electrical power switch is generally connected in series between a load and a power source in order to connect or disconnect (switch on or off) a load from an alternating current (AC) power source. When the switch is in the “ON” state, a generally low impedance appears between the terminals of the switch and electrical power will flow from the power source, for example, the AC mains, to the load. On the other hand, when the switch is in the “OFF” state, a very high impedance will generally appear across the terminals of the switch, thereby preventing or blocking the flow of electrical energy from the power source to the load.
A conventional two-terminal power switch generally includes a conductive contact switching member which is pivotable or movable between an “ON” and an “OFF” position corresponding respectively to the connection and or disconnection of the two terminals of the switch by the metallic conductive member.
Electronic switching devices such as power MOSFETS, transistors or thyristors are commonly used as switching means in electronic controlled electrical power switches since switching can be done without physically moving the conductive metallic member as in the case of conventional switches. However, the ON-state voltage drop across such devices is usually large and generates waste heat which causes heat dissipation problems, especially when the switch is enclosed in a small confined space, such as inside a wall socket.
Electro-mechanical switches such as relays which include a moveable conductive member connected to a magnetic core and coupled to a solenoid are also found in present day automated electrical power switches. However, conventional relay switches are usually bulky and require a continuous current to maintain a switching state. Such a continuous current causes heat dissipation problems as well as power supply problems. Electronic or electromechanical switching devices are particularly attractive nowadays because they can be used in soft-touch or automated switching schemes such as remote-control switching, motion-sensored or other detection-based power switching systems.
While soft-touch or automated switching schemes are generally preferred, such preferred switching schemes or devices generally require automated control and switching circuitry for controlling and/or effecting the actual switching. In addition, a power switch which is remotely controllable will provide great convenience to the public. However, such automated or remote controllable switching schemes generally require a power supply, usually a DC source but not necessarily limiting thereto, to operate the control and automated switching circuitry or the signal receivers.
For a three-wire AC wiring system, in which the live, neutral and earth terminals are available, the control or switching circuitry operating power may be obtained by connecting a power supply circuit between the “live” and the neutral or earth terminals. However, for a two-wire AC wiring system, in which the live or phase wire is connected through via a switching device, no neutral or earth terminals are available and the operating power supply may be obtained from an external power supply or directly from the AC power source. In the latter case, although the operating power may be obtained from the live wire alone or by additional wirings to the power source, this will usually involve additional wiring works which may be expensive and unsightly.
Obviously, it will be advantageous if the power supply to the control circuitry can be obtained directly from the live wire of the power source to which the switch is connected without requiring a separate power supply or additional wirings.
Where a power switch is used in location-fixed applications in a 2-wire environment, for example, for installation as a wall-mount power switch in a prewired wall socket, it may not be economical or practical to provide additional wirings to supply the necessary power. For such applications, an external power source will be inevitable unless the control and switching circuitry is line-powered. However, an external power supply usually means additional running costs as well as a more bulky and unsightly switching device.
Hence, it will be greatly advantageous if there can be provided switching devices or circuit arrangements in which the control or other peripheral circuitries can obtain their operating power from the live wire of the AC power source to which the switch is to be connected. However, since a power switch is usually connected in series with a load and between the two poles of an AC power source, the problems of getting line power to control switching are well known. In particular, a power switch is generally characterized by a high open-circuit voltage and a very low open-circuit leakage current when the switch is in the “OFF” state. At the same time, the switch is generally characterized by a low close-circuit voltage and a high close-circuit current across its two-terminals when the switch is on the “ON” state. Because of these inherent characteristics, problems exist for supplying operating power to the controlling and switching circuitries during both the “ON” and “OFF” state of a switch. Therefore, it will be advantageous if a two terminal power switch with line-powered switching and controlling circuitry (including remote-control circuitry) or circuit arrangements can be provided without undue complexity and in a sufficiently compact form.
In providing such line-powered circuitry or circuit arrangements, it will be highly advantageous if the additional on-state voltage drop across the terminals of the switch and the additional off-state leakage current due to the power supply to the control circuitry and the switching devices can be maintained to a minimum. A low off-state leaking current of less than 20 mA is generally required while a low on-state voltage drop is preferred since the product of the current and the voltage drop generally correlates to the power dissipation by the power switch itself.
In many conventional automated power switching circuitry, triacs or thyristors are usually utilized to facilitate electronic or non-contact power switching. Because of the inherent forward voltage drop of triacs or thyristors, power dissipation becomes significant and heat sinking requirements become critical. In higher current applications where a power switch is enclosed in a small and confined space during normal operation, for example, in a wall socket or cavity in case of a wall mounted power switch, triac or thyristor based switching devices may not be suitable due to the need of forced ventilation.
Hence, it will be of great advantage if there can be provided non-triac- or non-thyristor- based switching devices for use with the afore-described line-powered switching control circuitry to facilitate electronically controlled power switching while alleviating power dissipation problems associated with triac- or thyristor- based switching devices.
Furthermore, although electromechanical relay switches having a coil and a pair of normally open contacts have been proposed for use as switching devices in automated power switches, such relay switches have not been widely used in such power switches because a constant supply of DC current is generally required to maintain the mechanical conductive contacts
Lo Chung Ping Kevin
Yu Hui
Burns Doane Swecker & Mathis L.L.P.
Clipsal Asia Holdings Limited
Toatley , Jr. Gregory J.
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