Electrical transmission or interconnection systems – Switching systems
Reexamination Certificate
1999-05-06
2001-08-28
Ballato, Josie (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
C307S140000
Reexamination Certificate
active
06281604
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to apparatus for the control of a switch in an AC supply line and in particular, but not exclusively, for use with incandescent, halogen and fluorescent lamps.
In known electrical wiring schemes for lamps, the LIVE wire is usually singularly routed to the wall switch box for reasons of practicality, ease and economics. The absence of the NEUTRAL wire from the wall switch box excludes the possibility to derive a DC supply from the AC supply via the LIVE wire within the same switch box location by conventional means of a transformer which may be used for powering electronic circuits including control circuits, remote control receivers, ambient light controls, RF control receivers, timer controls and motion detection controls.
A switch circuit has been exposed in the prior art to derive a DC voltage from the LIVE wire while periodically switching the AC supply to the connected lamp load. The method employs a DC voltage derivation circuit in parallel with a solid state switch, and in series with said load along the LIVE wire. Such a switch circuit is marketed by X-10, Inc (USA). For the switch circuit to work, it is required that the lamp load is a pure resistance-which lies within an ohmic range in order for the DC voltage derived to be sufficiently high to operate the electronic circuits, while maintaining the power below a safety level such that excessive heat dissipation from the electronic circuits does not occur. This inherent disadvantage therefore restricts the application of the switch circuit to the electronic controlled switching of purely resistive lamp loads such as incandescent or filament lamps.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved switch circuit.
In accordance with a first aspect of the present invention, there is provided a switch circuit comprising an AC supply switching means and a triggering circuit for actuating said AC supply switching means, the triggering circuit including current sensing means for providing a triggering signal in response to a switch control signal and trigger delay means for delaying actuation of the AC supply switching means in response to the triggering signal.
Preferably, the AC supply switching means comprises a power triac connectable in series with a lamp load and the triggering circuit comprises an opto-coupled triac driver or a triac and an isolation transformer. It is also preferred that the trigger delay means comprises a resistor connectable at the trigger input of the preferred power triac.
There is also provided a multiple switch circuit comprising a plurality of circuits described above.
In accordance with a second aspect of the present invention, there is provided a DC voltage limiting circuit comprising a DC reservoir, a voltage reference means and a charging current interruption means, wherein the voltage difference between said DC reservoir and voltage reference means is compared to a pre-determined voltage level for the actuation of the charging current interruption means.
Preferably, the DC voltage limiting circuit comprises an electrolytic capacitor, a zener diode and a transistor to provide a controlled DC supply. The transistor pinches off the charging current to the DC reservoir.
In one example of the invention, the DC voltage limiting circuit further comprises another transistor which is arranged to form a Darlington pair with the first transistor.
However, in a preferred example of the invention, the DC voltage limiting circuit further comprises a capacitor coupled between the base of the transistor and the AC supply switching means and a discharge device in parallel with the capacitor. The advantage of using a capacitor is that it modifies the charging current waveform to help ensure more reliable switching than using a Darlington pair.
Typically, the discharge device in parallel with the capacitor comprises a transistor.
The features of the second aspect are usable with the first aspect.
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Ballato Josie
Polk Sharon
Smith-Hill and Bedell
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