CA1308772C

CA1308772C - Fluorescent lights

Info

Publication number: CA1308772C
Application number: CA 547090
Authority: CA
Inventors: To Yuen; Bong Chan; Chiu Yeung Poon; Chi Man Lui
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-09-17
Filing date: 1987-09-17
Publication date: 1992-10-13

Abstract

A B S T R A C T

A fluorescent lamp system in which an inductor (12) is connected in series with the cathodes (4, 6) of a gas discharge tube (2). Separate connections (14, 16) are tapped from the inductor (12) and also coupled to the cathodes of the tube. One connection includes a capacitor (18). Upon connection of an AC electrical supply a voltage builds up and discharges from the capacitor (18) at one cathode (4) as a surge voltage builds up at the other cathode (6). The resulting peak voltage at the cathodes is sufficient to immediately strike an arc in the tube (2).

Description

9~ r 1 308772 FLUORESCENT LIGHTS

S This invention relates fluorescent lamp~ in which a gas discharge tube i3 adapted to emit light by the stimulation of vapour within the tube. The operation of a gas discharge tube to emit light in this way is well known.
Known fluorescent lamp systems use a ballast coupled wlth a starter switch in order to generate a sufficient voltage to strike an arc in the ga~ discharge tube to initiate stimulation of tho vapour therein. Once initiated, the stimulation of the vapour can be sustained by a lower voltage. Thi~ known system normally results in the tube flashing a few tLmes before emitting continuous light, which flashing is itself disadvantageous as it reduces the effective life of the tube. A variety of ball4st designs have been proposed, each having advantages and disadvantages. However, each has a common problem in ~0 that it fails to operate at all when the supply voltage drops substantially, for example, by around 20S. This renders the system unsuitable for regions where a reliable mains suppIy is not available.
~ A system has been proposed which does not require ; 25 the use of a starter switch, and in which upon connection of the mains supply, the light emitted from the tube grows ~::

. .

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.

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~2~ 27876~1 gradually, and without flashing. While this system avoid~ the reduced life of the tube consequential upon flashing, the lamp will nevertheless fail to operate upon a substantial fall in the supply voltage.
According to the present invention, a ballast is used which comprises an inductor connected in series with the gas discharge tube, but separate connections to the tube are tapped from an intermediate length of the inductor. One of these connections includes a capacitor whereby upon connection of the mains supply, a voltage is built up in the capacitor for dis~
charge at one cathode of the tube to strike an arc therein.
Once struck, the arc is sustained by a lower voltage which is preserved across the tube through the other connection.
By appropriate selection of the number of turns in the inductor, the capacitor, and the tapped connections from the inductor, a lamp according to the invention can be adapted to operate over a broad range of supply voltages, for example, from as low as 140 volts to as high as 250 volt~. In a typical lamp according to the invention, a 20 to 40 watt fluorescent tube is connected to a mains supply through a ballast compris~
ing an inductor of around 1,000 turns, the tapped connections being spaced by around 600 turns adjacent one end of the coil.
In accordance with the present invention, there is provided a fluorescent lamp system comprising a gas discharge tube with cathodes at either end thereof; a ballast having an inductor connected in series with the cathodes of the discharge -2a~ 27876~1 tube and separate connections to the discharge tube tapped from the inductor and also coupled to the cathodes of the tube, one of the connections including a capacitor such that upon connection to an AC electrical supply a voltage is built up in the capacitor for discharge at one cathode of the discharge tube as a surge voltage is generated at the other cathode to establish a peak voltage sufficient to strike an arc in the tube.
An embodiment of the invention will now be described by way of example and with reference to the / accompanying schematic drawing, which shows a circuit incorporating a fluorescent gas discharge tube for coupling to an AC mains supply, The circuit illustrated shows a discharge tube 2 S having two cathodes 4, 6 connected via a switch ~not shown) to~an AC mains supply 8 through a ballast 10. The ballast 10 comprises an inductor coil 12 connected in series with the tube 2, and has two connections 14 and 16 ~apped therefrom. Connection 14 is tapped to the inductor coil through a capacitor 18, the connections 14 and 16 are themselves also coupled to the cathode~ 4 and 6 of the tube 2.
The circuit shown i9 suitable for illuminating a 20 to 40 watt fluore~cent tube from an AC mains supply of 200 volts. The inductor con~ists of a coil of 1,005 turns around a 6.5 sq.cm. core with a 0.26 mm. gap on the magnetic path. The tappings _ and c are spaced by 600 turns, equivalent an inductance of 0.4S Henries. The tapping b is ~paced from the end a of the coil by 400 turns (approximately 0.22 Henries~ and tapping c is ~paced from the other end d of the coil by 5 turns. The capacitance of the capacitor 18 is 7.6,ufd. The dispo~ition of the tappings a and b may be adjusted for different mains supply voltages.
25In the arrangement shown, the connection of the 200 volt AC supply will generate a peak voltage of around 1 3~8~

400 volt~ at connection 14, and a surge voltage as a pip of around 800 volts at connection 16. These voltages are in phase and the resulting peak voltage acros~ the cathodes of the tube 2 will be higher than 1,200 volts, resulting in the immediate striking of the arc therein. Once the arc is struck, the voltage across the cathodes will drop to around 100 volts, RMS, su~taining the arc and maintaining ths tube illuminated.
It will be appreciated that in the event of the mains supply falling by 20%, a surge voltage will be generated across the cathodes 4 and 6 in excess of 1,000 volts, qu~te Qufficient to ~trike an arc in the tube.
Further, ~n each ca~e, the arc will be ~truck immediately the circuit is connected to the mains supply, and preliminary fla~hing i~ avoided.
Fluorescent lamps adapted according to the invention can be effectively used in regions where the AC
mains supply varie~ over a relatively wide range. The sy~tsm illu~trated can be connected to supply voltages which vary between 140 and 250 voltQ, and rsmain effective, whereas comparable previous systems would cease to function at voltages below around 170 volts. It will be appreciated also that fluorescent lamp~ may be adapted according to the invention to operate in conjunction with ~upply voltages other than those referred above.

Claims

1. A fluorescent lamp system comprising a gas discharge tube with cathodes at either end thereof; a ballast having an inductor connected in series with the cathodes of the discharge tube and separate connections to the discharge tube tapped from the inductor and also coupled to the cathodes of the tube, one of the connections including a capacitor such that upon connection to an AC electrical supply a voltage is built up in the capacitor for discharge at one cathode of the discharge tube as a surge voltage is generated at the other cathode to establish a peak voltage sufficient to strike an arc in the tube.

2. A system according to Claim 1 wherein the disposition of the tapped connections on the inductor is adjustable.

3. A system according to Claim 1 or Claim 2 wherein the inductor and tapped connections including the capacitor are in-cluded in a single ballast unit.