GB2278023A

GB2278023A - Fluorescent tube control system

Info

Publication number: GB2278023A
Application number: GB9406816A
Authority: GB
Inventors: Jeffrey Dennis Evemy
Original assignee: EVTACON Ltd
Current assignee: EVTACON Ltd
Priority date: 1993-05-12
Filing date: 1994-04-06
Publication date: 1994-11-16
Also published as: GB9309753D0; GB9406816D0

Abstract

This is a technique for lighting special effects using conventional fluorescent tubes. The system employs a control system which allows high-speed starting and full dynamic control of the tube. High speed starting is supported by a continual heater supply together with a bridge rectifier and diode-capacitor voltage multiplier which provides a high direct voltage to start the tube. After starting, the bridge rectifier and the diodes of the voltage multiplier provide a direct path from the AC input to the tube (Fig 2). Dynamic control of the tube is effected by interruption of the AC input to the rectifier and voltage multiplier, eg. by use of a triac or relay. <IMAGE>

Description

FLUORESCENT TUBE CONTROL SYSTEM DESCRIPTION This invention is a technique for high speed control of conventional fluorescent tubes for lighting special effects.

Electronic lighting systems incorporating fluorescent tubes are not widely used for special effects such as are required by night-clubs, live musicians and amusement fairs. This is due to the difficulty of starting the tube quickly to control its effect. Indeed, where controlled lighting of this type is required; inert gas discharge tubes such as argon or neon are to be preferred despite their fir greater cost.

The user of fluorescent tubes for lighting effects presently has two options; quicker 'starterless' circuits may be used, often requiring special, more expensive tubes and not allowing the fast on-off control necessary for chasing patterns. Alternatively, conventional tubes offer certain display advantages (such as IJitraviolet) but may not be dynamically controlled.

The invention presented here employs an electronic system capable of very high-speed starting and control intended for conventional (lower-cost) fluorescent tubes; high-speed starting is supported by a continual heater supply together with a capacitive voltage multiplier and rectifier operating from an AC mains input, a conventional inductive ballast and associated power factor correction are used.

A specific embodiment of the invention will now be described by way of the example illustrated in the accompanying figures.

Figure 1 shows an outline block diagram of an implementation of this system Figure 2 shows details ofthe voltage multiplier section.

Referring to Figure 1 outlining the complete system; the operation ofthe technique is as follows: The AC mains input is passed via the ballast to two independent circuit elements; the control circuit, and the heater supply. The heater supply continually provides a low voltage to the cathode of the tube; regardless of the state of the tube (on or of) this supply is maintained. Note that as a DC supply to the tube is employed, only one end ofthe tube needs to be heated.

The ballast is an inductive element of the proprietary type normally used for fluorescent tubes; its rating corresponds to the tube rating in the normal manner. Note that as this is used in a series circuit the full AC characteristics at this point do not differ from a conventional system Note also that the heater supply can (though need not necessarily) be derived after the ballast voltage drop; this has the effect of reducing the heater supply when the tube is alight for longer periods, reducing overall power consumption.

The control element is any form of AC control; such as a TRIAL or relay, this may be controlled externally to switch the tube on or off accordingly. Alternatively, if the heater supply is powered from a separate AC source, the control block may be bypassed and any external control of the AC supply to the ballast will control the tube directly.

The voltage multiplier and rectifier provides two distinct functions; First it generates the high voltage necessary to 'strike' the tube, secondly it rectifies the AC supply to provide the DC power to the tube. As the operation of this section is crucial to the design it is described in more detail below: Referring to Figure 2, which illustrates example circuitry of the voltage multiplier and rectifier; the labelling of components is for identification purposes only and is entirely arbitrary. At all times the bridge rectifier operates in the conventional manner and the orientation of all the other diodes ensures that a direct path is available from AC input terminals to the tube, providing the power when the tube is alight. Before the tube has struck there is no effective load across the output terminals 'p' and 'm' and the operation ofthe voltage multiplier network within the dotted box may be considered in isolation, and described on a cycle by cycle basis as follows.

During the first phase ofthe mains cycle (arbitrarily defined as when point 'x' is negative with respect to point 'y') current flows through D2 to point 'a', charging capacitors C1 and C3 (via D5 and D6) to the full supply voltage V, with points 'a' and c' representing the positive plates. During phase 2 ofthe supply (when 'xl is positive with respect to 'y') the voltage ofC1 (V) is added to the voltage at 'x' (V) causing a current to flow through D5 to charge C2 to a voltage greater than V. Similarly a current flows through D7 transferring charge from C3 to C4, raising the potential ofpoint 'd'. It can be seen that during subsequent phases current flows alternately from C1 to C2 via D5, and from C3 to C4 via D7 when Ix' is positive with respect to 'y'; and from C2 to C3 via D6, and from the supply to C1 via D2 when tyl is positive with respect to 'x'. Over several cycles, the net effect is a current from 'a' to 'd' (continuing through additional elements if present to point 'p'), transferring charge along the chain toward the final capacitor, generating a high positive voltage potential at point 'p'.

Note that the arrangement shown in Figure 2. is not unique; any number of diode and capacitor elements may be included in the chain to generate the required striking voltage. A similar arrangement (with the diodes reversed) may be inserted in the negative supply (between points 'n' and 'm'), to generate a high negative potentiaL Any combination of such positive or negative voltage muEtipliers, with similar or dissimilar numbers of elements can be employed to generate the high voltage required to 'strike' the tube.

Claims

1 A fluorescent lighting control system which allows high-speed starting and control for conventional (lower-cost) fluorescent tubes; high-speed starting is supported by a continual heater supply together with a dual operation voltage multiplier and rectifier operating from an AC mains input, control is provided directly by interruption of the AC supply to the voltage multiplier and rectifier.

2 A fluorescent lighting control system using the architecture of claim 1, wherein the necessary ballast is implemented by a series inductive element in the AC path to the voltage multiplier and rectifier.

3 A fluorescent lighting control system using the architecture of claims 1 or 2, wherein the control is provided by use of a low voltage controlled or optically coupled semiconductor switch such as a TRIAC.

4 A fluorescent lighting control system using the architecture as claimed in any preceding claim, wherein the circuitry is designed specifically to support conventional fluorescent tubes including coloured and ultraviolet types.

5 A fluorescent lighting control system using the architecture as claimed in any preceding claim, wherein the voltage multiplier and rectifier is substantially as described herein with reference to Figure 2 ofthe accompanying drawing.

6 A fluorescent lighting control system substantially as described herein with reference to Figure

1 ofthe accompanying drawing.