GB2393859A

GB2393859A - Dimmable lighting

Info

Publication number: GB2393859A
Application number: GB0219586A
Authority: GB
Inventors: Martin Tebbs
Original assignee: TRAYPOINT Ltd
Current assignee: TRAYPOINT Ltd
Priority date: 2002-08-22
Filing date: 2002-08-22
Publication date: 2004-04-07
Also published as: GB0219586D0

Abstract

A lighting system for connecting a plurality of lighting units 3 to a power supply line 2 includes a plurality of electronic transformers 1 each connected in parallel with the supply line 2 and each operable to transmit power to one of the lighting units 3. A Selectively controllable dimmer 4 is connected in parallel with the power supply line 2 and is operable to transmit to each transformer 1 a demand signal whose waveform mirrors the selected setting of the dimmer 4. Electronic circuitry connected to or forming part of each transformer 1 is operable to receive each demand signal from the dimmer 4 and to vary the power supplied by the transformer 1 to the respective lighting unit 3 as a function of the demand signal received from the dimmer 4.

Description

LIGHTING SYSTEMS

This invention relates to lighting systems for connecting a plurality of lighting units whose intensity can collectively be controlled through a central dimmer device.

Dimming devices are well known and find application in numerous environments ranging from high powered lighting systems for general illumination to relatively low powered requirements for use in private dwellings. Instead of having individual dimming circuits for each lighting appliance it is often preferred to adopt a central dimming device to control the intensity of a plurality of lighting units connected in parallel to a power supply line. Conventionally such dimming devices are connected in series with the lighting appliances, the power supplied to some lighting units being controlled through a step down converter function of a transformer. One major disadvantage with such systems is that the dimming device can readily be overloaded should the power requirements of the lighting appliances exceed the maximum rating of the dimmer device. In this event the heat dissipated at the dimmer device may become excessive.

One object of the present invention is to provide a lighting system which overcomes, or at least alleviates, many of the disadvantages to be found in systems such as those discussed above.

In one aspect, the invention provides a lighting system for connecting a plurality of lighting units to a power supply line, the system including a plurality of electronic transformers each connected in parallel with the supply line and each operable to transmit power to one of the lighting units, selectively controllable dimming means connected in parallel with the power supply line and operable to transmit to each transformer a demand signal whose waveform mirrors the selected setting of the dimming means, and electronic circuitry connected to or forming part of each transformer and operable to receive each demand signal from the dimming means and to vary the power supplied by the transformer to the respective lighting unit as a function of the demand signal received from the

dimming means.

Preferably, the demand signals transmitted by the dimming means comprise phase angle demand signals.

In a preferred embodiment of the invention, the electronic circuitry operates to provide a measure of the timing between sequential firing points of a demand signal, compares this measured value with a measure of the timing between the first of these firing points and the following switch off point and calculates from these measured values a ratioed output for controlling the power supplied to the respective lighting unit.

The ratioed output may be expressed as 2B where A is the first measured value and B is the second measured value.

The electronic circuitry may comprise a microchip which forms part of each electronic transformer, the output from the microchip being transmitted to a high frequency step down converter from which the respective lighting appliance is supplied.

The invention will now be described by way of example only with reference to the accompanying diagrammatic drawings in which: Figure 1 is a circuit diagram illustrating a lighting system in accordance with the invention; Figures 2A and 2B diagrammatically show wave forms illustrative of output demand signals from a dimmer which forms part of the lighting system; and Figure 3 is a block diagram illustrating an electronic transformer which forms part of the lighting system illustrated in Figure 1.

As shown in Figure 1, a plurality of electronic transformers 1 are connected in

parallel in a power supply line 2 of a mains source of alternating current. The live and neutral connections of the supply line 2 are indicated by references L, N respectively and each transformer is connected to control the level of power supplied to one of a plurality of lighting appliances 3. These appliances can comprise any conventional light or lamp including fluorescent and incandescent lighting appliances. Five transformers 1 and lighting appliances 3 are shown in Figure 1. In practice, a much larger number of transformer supplied appliances may be employed.

A manually or automatically controlled dimmer device 4 is connected in parallel with the power supply line 1 and operates to transmit a demand signal to each electronic transformer 1 via a power line 5. The dimmer device 4 outputs a phase angled signal whose waveform conforms with its selected setting. Thus, when at its maximum setting the waveform of the output signal is essentially as shown in Figure 2A and conforms essentially to a conventional sine wave. At a setting below its maximum, the wave form essentially conforms to the stepped waveform shown in Figure 2B. Firing points of the phase angled signals are indicated by reference numeral 6 in Figure 2B with switch off points indicated by reference numeral 7. It will be understood that selective manipulation of the dimming device will vary the positions of the firing and switch off points of the output signals.

Each electronic transformer 1 includes an electronic chip which is connected to receive the phase angled demand signal of the dimmer device 4 and operates to deliver to a frequency step down converter of the transformer an output signal which corresponds to the demand signal received from the dimmer device. This signal then controls the level of power supplied to the respective lighting appliance.

In a preferred embodiment, the chip operates to provide a measure of the timing between sequential firing points of a demand signal, compares this measured value with a measure of the timing between the first of these firing points and the following switch off point and calculates from these measured values a ratioed output for controlling the power supplied to the respective lighting unit.

The ratioed output may be expressed as 2A where A is the first measured value and B is the second measured value.

The measured values A and B are shown in Figure 2B.

The electronic transformer illustrated in Figure 3 comprises a filter 10 for removing interference present in the power supplied, a rectifier 11 which operates to convert mains alternating current to direct current, a power supply unit 12, the previously discussed electronic chip 14, and a high frequency step down converter 15 which operates to convert the rectified direct current supply to the required high frequency low voltage source for powering each lighting appliance 3. Demand signals from the dimmer device are received by the transformer via a selector switch 16. Each transformer also includes an indicator lamp 17 which operates to show the status of the transformer and a temperature sensor 18 Sensed temperatures are transmitted to the electronic chip 14. Output signals from the electronic chip 14 are transmitted to the step down converter 15 to control the power supplied to the respective lighting appliance in dependence upon the setting of the dimmer device 4.

It will be appreciated that power control to the appliances is possible by having the electronic chip circuit directly control the operation of the high frequency step down converter. This can be achieved by causing a variable number of consecutive cycles to be missed, by introducing a delay between each high frequency cycle or a combination of these methods. In a preferred arrangement, a block of cycles is missed out corresponding to the off time indicated by the dimming signal and a delay between individual high frequency cycles further reduces power if the temperature goes too high or an overload is detected. In an alternative arrangement, power to the appliances is controlled by altering the amplitude of the sine wave.

Advantages which accrue from lighting systems in accordance with the invention

include the fact that whole banks of individual dimmers can be replaced by a single central dimmer; also, existing lighting systems can be extended without adding significant load to the dimmer.

It will be appreciated that the foregoing is merely exemplary of lighting systems in accordance with the invention and that various modifications can readily be made to the lighting system described without departing from the true scope of the invention.

Claims

1. A lighting system for connecting a plurality of lighting units to a power supply line, the system including a plurality of electronic transformers each connected in parallel with the supply line and each operable to transmit power to one of the lighting units, selectively controllable dimming means connected in parallel with the power supply line and operable to transmit to each transformer a demand signal whose waveform mirrors the selected setting of the dimming means, and electronic circuitry connected to or forming part of each transformer and operable to receive each demand signal from the dimming means and to vary the power supplied by the transformer to the respective lighting unit as a function of the demand signal received from the dimming means.

2. A system as claimed in claim 1 wherein the demand signals transmitted by the dimming means comprise phase angle demand signals.

3. A system as claimed in claim 1 or claim 2 wherein the electronic circuitry operates to provide a measure of the timing between sequential firing points of a demand signal, compares this measured value with a measure of the timing between the first of these firing points and the following switch off point and calculates from these measured values a ratioed output for controlling the power supplied to the respective lighting unit.

4. A system as claimed in claim 3 wherein the ratioed output is expressed as A where A is the first measured value and B is the second measured value.

5. A system as claimed in any one of the preceding claims wherein the electronic circuitry comprises a microchip which forms part of each electronic transformer, the output from the microchip being transmitted to a high frequency step down converter from which the respective lighting appliance is supplied.

6. A lighting system as herein described and as described with reference to the accompanying diagrammatic drawings.