GB2028027A

GB2028027A - Device for regulating the brightness of fluorescent lamps

Info

Publication number: GB2028027A
Application number: GB7926498A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-07-31
Filing date: 1979-07-30
Publication date: 1980-02-27
Also published as: FR2432817B3; CH630766A5; DE2838432A1; GB2028027B; FR2432817A1

Abstract

A brightness regulating device (1) for a fluorescent lamp (8) contains a semi-conductor switch (11) connected in series with the lamp. The semiconductor switch (11) is phase-shift controlled by a device (12). An incandescent lamp (16) is connected in shunt with the semiconductor switch (11), or parallel to a series connection of the semiconductor switch (11) and an interference filter (13), (14), (15). The lamp (16) maintains a small glow discharge current in the fluorescent lamp (8) when the switch (11) is open. By this means the brightness regulation range can be broadened in the direction of shorter switching times. In addition, electrical and acoustic interference and noise phenomena at the filters and ballast are reduced. <IMAGE>

Description

SPECIFICATION A device for regulating the brightness of fluorescent lamps The invention relates to a device for regulating the brightness of a.c. fluorescent lamps.

Devices with controlled semiconductor switches for regulating brightness are used with fluorescent lamps, which either are equipped with filament transformers and external means to assist ignition, or with only a glow starter. A series of reactor or ballast is of course provided in each case.

The brightness range is greatest if the fluorescent lamps are equipped with filament transformers in their driving circuits, particularly if in addition means are provided to assist ignition.

Lighting installations in which only a glow starter is used, exhibit a smaller brightness range because ignition capability is less on account of the lack of external heating of the electrodes, and consequently the magnitude of the permissible electrode-current averaging time is less. The result is that, in the case of short electrode-current averaging times, the voltage at the glow starter is increased, on account of the voltage kick-back of the ballast, by such an amount that the starter is reactuated. This produces an erratic operation and reduces the life of the glow starter.

A glow starter is of course a cheap component and can readily be replaced. However, in light fixtures the glow starters are often enclosed and accordingly it is a difficult and time-consuming operation to replace them.

Since it is often desired to be able to regulate existing light fixtures containing fluorescent lamps provided with glow starters without having to interfere with the fittings or mountings of the fluorescent lamps, a relatively small brightness regulation range must therefore be accepted in order to avoid overloading the glow starter.

A further disadvantage of known devices for regulating the brightness of fluorescent lamps by means of controlling the phase shift, is the fact that undesirable electrical and acoustic disturbances and noise phenomena are produced by the chopping of the mains current. On the one hand this involves overshooting the interference filters which have to be incorporated for reasons of radio interference suppression, and on the other hand hum phenomena occur at the ballast as a result of magnetostriction.

An object of the invention is to raise the ignition capability of fluorescent lamps by devices of the type heretofore described, without interfering with their fittings or mountings, and at the same time to avoid the electrical and acoustic interference phenomena that occur on switching on the a.c. circuit.

According to the invention there is provided a device for regulating the brightness of a fluorescent lamp provided with a phase-shift controlled semiconductor switch connectable to the lamp so that its main terminals lie in series with the fluorescent lamp, characterised in that an incandescent lamp (16) is connected in shunt across the main terminals of the semiconductor switch (11), so that in use during the shut-off periods of the semiconductor switch 11, it supplies the fluorescent lamp (8) with a voltage that does not produce automatic ignition of the fluorescent lamp (8) but maintains in said lamp (8) a glow-discharge current that is small compared to the operating current of the ignited state of the lamp.

It has been found that by means of the invention, the ion concentration in the fluorescent lamps can be increased during the switch-off state of the semiconductor switch in each half-wave of the a.c. current and thereby produce a larger ignition capability when the semi-conductor switch is switched on again, and reduce the voltage rise at the glow starter.

Moreover, the damping effect produced by the incandescent lamp connected in the shunt causes a marked reduction in overshooting phenomena at the interference filters and acoustic humming in the ballast.

Embodiments of the invention will now be described hereinafter with reference to the accompanying drawing, which illustrates a simplified circuit diagram of a regulating device and a fluorescent lamp with a series reactor and glow starter, connected to said device.

The regulating device 1 of the circuit shown in the drawings is provided with input terminals 2 and 3 for connection to a single-phase or multi-phase a.c. circuit.

The circuit shown includes a lighting device 6 having a series reactor or ballast 7, a fluorescent lamp 8 and a glow starter 9 with a capacitor 10 connected in parallel across the starter 9.

The device 6 is connected to output terminals 4 and 5 of the regulating device 1,to which the regulated output voltage of the mid-point or zero conductor Mp is applied. For the sake of simplicity only a single fluorescent lamp with a series reactor and glow starter is shown in the drawing. Normally however, a plurality of lighting devices 6 are connected in parallel to the output terminals 4, 5.

The contact-break distance of a semiconductor switch 11, in fact a triac, lies between the terminals 2 and 4, the control electrode of the triac being connected to a control device 12. The control device 12 transmits to the semiconductor switch 11 control signals necessary for regulating a phase shift. Connections from the control device 12 to the circuit terminals 2,3 as well as adjustment devices for the control device 12 are not shown in the drawing.

An interference filter comprising two chokes 13, two capacitors 14 and a discharge resistor 15 is also connected on the output side between the semiconductor switch 11 and the output terminal 4.

An incandescent lamp 16 is connected in shunt to the semiconductor switch 11. The continuous lines show how the incandescent lamp 16 is connected directly parallel to the contact-break distance of the semiconductor switch 11, i.e. at its input and output.

Since this arrangement requires additional internal wiring of the regulating device 1,the incandescent lamp 16 may also be connected in the manner shown by the dotted lines to the input terminal 2 on the phase conductor side and to the output terminal 4, which can be effected in an advantageous manner without interfering with the circuitry of an already existing regulation device 1. The incandescent lamp 16 is then parallel to the series connection of the semiconductorswitch 11 and filter 13,14,15.

It is clear that the fluorescent lamp 8, as a result of the shunting effect of the incandescent lamp 16, will be connected to the a.c. circuit if the semiconductor switch 11 is opened, determined by the control device 12, of each half wave of the feed voltage.

Thus, by suitable choice of the power of the incandescent lamp 16, automatic ignition of the fluorescent lamp 8 cannot take place before the semiconductor switch 11 is closed. However, a glow discharge occurs in each case on one electrode of the fluorescent lamp, and results in a higher ion concentration. Thus, ignition of the fluorescent lamp 8 occurs during subsequent closing of the semiconductor switch 11.

In the illustrated arrangement of a conventional glow starter 9 connected parallel to the electrodes of the fluorescent lamp 8, the voltage at the glow starter 9 does not rise sufficiently high so as to actuate the latter. It is thus possible by means of the invention to broaden the regulation range in the direction of smaller electrode-current averaging times.

It is also clear that the incandescent lamp as arranged dampens the interference filters 13,14,15 and also the ballast 7, which greatly reduces electrical and acoustic interference and noise phenomena.

Depending on the number of fluorescent lamps 8 connected to the terminal 4,5, the incandescent lamp 16 can be suitable for an output of 40-200 watts at 220 v. The arrangement of an incandescent lamp is accordingly advantageous because it has PTCresistor properties, furthermore can be installed in a simple manner in such a way that heat dissipation is no problem, and finally because its brightness automatically and directly provides an optical indication of the prevailing regulation state. The losses as a result of heat generation by the incandescent lamp in this connection rise only slightly, and are of the order of magnitude of 1% of the total power provided by the circuit. Compared with these small losses there is the advantage that even in the case of fluorescent lamps provided with glow starters, a light regulation of 100 to about 30 /O is possible, instead of the previously best regulation of 50%, without having to provide filament transformers, special starters, ignition strips, or the like.

A 60 w (220 v) incandescent lamp is used in a given example with a rated current of 10 amps. The heat losses from this lamp are about 25w at the minimum value of the output voltage. By comparison, the minimum output at the florescent lamps can be reduced from 1100 VA (50%) to 660 VA (30%). This corresponds to a gain of 440 VA compared to additional losses of 25w or 25 VA.

Claims

1. A device for regulating the brightness of a fluorescent lamp provided with a phase-shift controlled semiconductor switch connectable to the lamp so that its main terminals lie in series with the fluorescent lamp, characterised in that an incandescent lamp (16) is connected in shunt across the main terminals of the semiconductor switch (11), so that in use during the shut-off periods of the semiconductor switch (11), it supplies the fluorescent lamp (8) with a voltage that does not produce an automatic ignition of the fluorescent lamp (8) but maintains in said lamp (8) a glow-discharge current that is small compared to the operating current of the ignited state of the lamp.

2. A device according to Claim 1, characterised in that an interference filter, (13,14,15) is arranged in series with the semiconductor switch (11), the incandescent lamp (16) being connected in parallel with said series arrangement.

3. A device according to any preceding claim characterised in that the semiconductor switch (11) is a triac.

4. A device for regulating the brightness of a fluorescent lamp substantially as hereinbefore described with reference to the accompanying drawing.