GB2242323A

GB2242323A - Variable output fluorescent lighting apparatus

Info

Publication number: GB2242323A
Application number: GB9006260A
Authority: GB
Inventors: Cheng-I Chiang
Original assignee: CHIANG CHENG I
Current assignee: CHIANG CHENG I
Priority date: 1990-03-20
Filing date: 1990-03-20
Publication date: 1991-09-25
Also published as: GB9006260D0

Abstract

When a switch SW2 is open a tapped voltage from a transformer T3 is applied across one electrode only of a fluorescent lamp to produce a slight glow, closure of switch SW2 causing the whole output of transformer T3 to be applied between the lamp electrodes to produce the full light output. A capacitor C3 may be adjusted to vary the glow output. The transformer T3 is energised by a high frequency oscillator 3 which is powered from a mains supply 2, and automatic changeover to a battery supply may be incorporated (Fig 3). A similar oscillator 3' and a voltage multiplier 4' energise wires 5a, 5b to electrocute insects attracted by the glow from lamp L.A desk lamp, (Fig 4), may incorporate a central lamp with the charged wires therearound, control circuitry being housed in a top cover. <IMAGE>

Description

VARIABLE OUTPUT FLUORESCENT LIGHTING APPARATUS The invention relates to apparatus for enahling a fluorescent lamp to have a variable light intensity output.

The fluorescent lamp is widely used for lighting purposes. It comes in different shapes and sizes to allow variations in lighting. A fluorescent bulb applied to a small night lamp has a size substantially smaller than that of an ordinary ceiling lamp. The intensity of light output of the night lamp is less but can still provide ample illumination. A fluorescent lamp used in an electrical device for insect control gives off a dim light which attracts insects such as mosquitoes and the like. The electrical device has a plurality of slightly spaced high voltage, low current, alternately charged wires. When an insect comes into contact with the wires, it gets electrocuted.

It is possible to control a fluorescent lamp to allow it to have the illumination of a ceiling lamp or that of a night lamp, thus making it unnecessary to buy both lamps. One method of doing this is to have a variable resistor to control the illumination of the lamp. However, the variable resistor has a logarithmic behavior which makes it difficult to control the illumination of the lamp. Furthermore, the variable resistor does not help stabilize the supply of current to the lamp. This instability causes "flickers" which shorten the life of the lamp.

According to the present invention, variable output fluorescent lighting apparatus for a fluorescent lamp having first and second electrodes comprises means for supplying an alternating current voltage signal; means for feeding a portion of said alternating current voltage signal to said first electrode of said fluorescent lamp; and switching means for selectively connecting said second electrode of said fluorescent lamp to said alternating current voltage supply means; said feeding means being arranged to provide said fluorescent lamp with voltage and current sufficient to cause said fluorescent lamp to glow with a first intensity; and the arrangement being such that, when said second electrode of said fluorescent lamp is electrically connected to said alternating current voltage supply means, said first and said second electrodes receive sufficient voltage and current to cause said fluorescent lamp to glow with a second intensity brighter than said first intensity.

With this arrangement, the intensity of light output of the lamp may be varied without causing instability in the supply of current to the lamp.

Preferably the apparatus further comprises means for supplying a direct current voltage, said alternating current voltage supply means being arranged to be triggered by said direct current voltage supply means to generate said alternating current voltage signal.

The alternating current voltage supply means may comprise: a resistor having a first terminal electrically connected to a positively charged terminal of the direct current voltage supply means; a capacitor having a first terminal electrically connected to a second terminal of the resistor, and a second terminal electrically connected to a negatively charged terminal of the direct current voltage supply means; a transformer having a primary winding electrically connected across the capacitor; and a transistor having a base terminal electrically connected to a first portion of the primary winding, and a collector and an emitter electrically connected across a second portion of the same. This arrangement acts as an oscillating circuit triggered by the voltage output af the direct current voltage supply means.A secondary winding of the transformer may have a tapped portion and the feeding means include a variable capacitor connected across the first electrode of the fluorescent lamp and the tapped portion of the secondary winding.

The invention will now be described by way of non-limiting embodiments with reference to the accompanying drawings, in which: Figure 1 is a schematic circuit diagram of a first preferred embodiment of variable output fluorescent lighting apparatus according to the invention; Figure 2 is a schematic circuit diagram of a second preferred embodiment of variable output fluorescent lighting apparatus according to this invention; Figure 3 is a schematic circuit diagram of a modification to the arrangements shown in Figures 1 and 2; and Figure 4 is a perspective view of a desk lamp according to this invention.

Referring to Figure 1, the apparatus has has an alternating current (AC) signal input terminal 1. A power supply switch SW1 electrically connects the input terminal 1 to the primary winding of a step down transformer T1. The secondary winding of the transformer T1 is connected to diodes D1-D4, which are configured as a full-wave bridge rectifier circuit. The diodes D1-D4 have a rectified direct current (DC) voltage signal output which is filtered by a capacitor filter C1. The capacitor C1 has a positively charged terminal connected to a first terminal of a resistor R1. A negatively charged terminal of the capacitor C1 is connected to a second terminal of a capacitor C2.A second terminal of the resistor R1 and a first terminal of the capacitor C2 are tied together at a common node.

The capacitor C2 is connected in parallel with the primary winding of a transformer T2. A first portion of the primary winding of the transformer T2 is connected to the base of a transistor Q. The collector and the emitter of the transistor Q are connected in parallel across a second portion of the same. The resistor R1, the capacitor C2, the transformer T2, and the transistor Q act as a high frequency oscillating circuit 3, which is triggered by the voltage output of the capacitor C1. A fluorescent lamp L is connected across the secondary winding of the transformer T2. A variable capacitor C3 is connected across a first electrode of the lamp L and a tapped portion of the secondary winding of the transformer T2. A selective switch SW2 electrically connects a second electrode of the lamp L to a second end of the secondary winding of the transformer T2. The capacitor C3 is continuously charged by a portion of the voltage across the secondary winding of the transformer T2 and feeds the lamp L with adequate voltage and current to allow the same to glow slightly. The capacitance of the capacitor C3 can be adjusted to allow the lamp L to have varying light intensity output.

When the switch SW2 is closed, the potential difference generated between the first and second electrodes of the lamp L causes said electrodes to release more electrons into the lamp tube. Since the lamp L is already glowing, less voltage is required to fully light the lamp L. Another advantage is that the annoying "flickers" commonly associated with conventional electrical circuits for fluorescent lamps are eliminated. The elimination of the "flickers" thus helps to prolong the life of the lamp L.

A second preferred embodiment is shown in Figure 2. The second preferred embodiment includes the electrical circuit of Figure 1 and an electrical insect control means 5. A second oscillating circuit 3', similar to the one found in the first preferred embodiment, comprises a resistor R', a capacitor C' connected in series with the resistor R', a transformer T2' having a primary winding in parallel with the capacitor C', and a transistor Q'. A first terminal of the resistor R' is connected to the positively charged terminal of the capacitor filter C1.

The voltage at the secondary winding of the transformer T2' serves as an input to a voltage multiplying or voltage doubler circuit 4. A first output terminal of the voltage doubler circuit 4 is connected to a first set of charged wires 5a of the electrical insect control means 5. A second output terminal of the voltage doubler circuit 4 is connected to a second set of charged wires Sb of the electrical insect control means 5. The first and second sets of charged wires 5a, 5b are alternately arranged and separated by a very small distance. When the lamp L glows, the generated light output attracts insects to fly into the charged wires. 5a, 5b and they are thus electrocuted.

A modificatibn to the circuitry of Figures 1 and 2 is shown in Figure 3. A diode D6 has a first terminal electrically connected to a secondary winding end of the transformer T1 and a second terminal electrically connected to a coil of a relay 5. A movable contact of the relay 5' is connected to a normally open NO contact of the same when current traverses the first diode D6.

The NO contact of the relay 5'is connected to the positively charged terminal of the capacitor C1.

Current coming from the full-wave bridge rectifier circuit is thus directed towards the oscillating circuit 3. A second diode D6' has a first terminal end similarly connected to the rectifier circuit and a second terminal end connected to a positive terminal of a rechargeable DC battery V and to a normally closed NC contact of the relay 5'. The battery V is continuously charged by current coming from the rectifier circuit.

When the AC signal input terminal is disconnected from the AC signal source, no current traverses the first diode D6 and the movable contact of the relay 5' is connected to the NC contact of the same. Electric power to the lamp L is now supplied by the battery V.

A desk lamp according to this invention is shown in Figure 4. The desk lamp comprises a circular base D, a fence grill E surrounding the peripheral edge of a top face of the base D, a lamp G centrally and vertically disposed on the top face of the base D, a plurality of alternately charged wires F surrounding the lamp G, and a cover H disposed on a top end of the fence grill E. A selective switch L is disposed on a top face of the cover H. The cover H contains a rechargeable DC battery J and an electrical circuit K for the lamp G.

A fluorescent lamp according to this invention has a wide variety of uses. The elimination of the "flickers" associated with conventional electrical circuits for fluorescent lamps prolongs the life of the lamp.

Claims

1. Variable output fluorescent lighting apparatus for a fluorescent lamp having first and second electrodes, the apparatus comprising: means for supplying an alternating current voltage signal; means for feeding a portion of said alternating current voltage signal to said first electrode of said fluorescent lamp; and switching means for selectively connecting said second electrode of said fluorescent lamp to said alternating current voltage supply means; said feeding means being arranged to provide said fluorescent lamp with voltage and current sufficient to cause said fluorescent lamp to glow with a first intensity; and the arrangement being such that, when said second electrode of said fluorescent lamp is electrically connected to said alternating current voltage supply means, said first and said second electrodes receive sufficient voltage and current to cause said fluorescent lamp to glow with a second intensity brighter than said first intensity.

2. The apparatus according to claim 1, further comprising means for supplying a direct current voltage, said alternating current voltage supply means being arranged to be triggered by said direct current voltage supply means to generate said alternating current voltage signal.

3. The apparatus according to claim 2, wherein said alternating current voltage supply means comprises: a resistor having a first and a second terminal, said first terminal being electrically connected to a more positively charged terminal of said direct current voltage suppy means; a capacitor having a first terminal electrically connected to said second terminal of said resistor and a second terminal being electrically connected to a more negatively charged terminal of said direct current voltage supply means; a transformer having a primary winding and a secondary winding, said primary winding having a first and a second portion and being electrically connected across said capacitor; and a transistor having a base terminal electrically connected to said first portion of said primary winding, and a collector and an emitter electrically connected across said second portion of said primary winding; whereby said resistor, said capacitor, said transformer and said transistor are arranged to act as an oscillating circuit.

4. The apparatus according to claim 3, wherein said secondary winding of said transformer has a tapped portion and said feeding means comprises a variable capacitor connected in use across said first electrode of said fluorescent lamp and said tapped portion of said secondary winding.

5. The apparatus according to claim 3 or claim 4, further comprising: a second alternating current voltage signal generating means electrically connected to the more positively charged terminal of said direct current voltage supply means; voltage multiplying means electrically connected to said second alternating current voltage signal generating means and having first and second output terminals; a first set of wires electrically connected to said first output terminal of said voltage multiplying means; and a second set of wires electrically connected to said second output terminal of said voltage multiplying means, each wire of said first and second sets of wires being positioned adjacent to one of said wires of the other set of wires.

6. The apparatus of any one of claims 2 to 5, wherein said direct current voltage supply means comprises: an alternating current voltage signal input terminal; a step down transformer having a primary and a secondary winding, said primary winding being electrically connected to said alternating current voltage signal input terminal; rectifying means electrically connected to said secondary winding of said step down transformer and having a rectified direct current voltage signal as an output; and means for filtering said rectified direct current voltage signal, said filtering means having a more positively and a more negatively charged terminal.

7. The apparatus according to any one of claims 2 to 6, wherein said direct current voltage supply means further comprises: a relay switch having a coil, a normally open contact electrically connected to the more positively charged terminal of said filter means, a normally closed contact and a movable contact; a first diode having a first terminal electrically connected to said secondary winding of said step down transformer and a second terminal electrically connected to said coil of said relay switch; a second diode having a first terminal electrically connected to said normally open contact and a second terminal electrically connected to said normally closed contact; ar.d a rechargeable battery having a positive terminal electrically connected to said second terminal of said second diode and to said normally closed contact of said relay switch; said movable contact being electrically connected to said normally open contact when current passes through said first diode; and said movable contact being electrically connected to said normally closed contact when no current passes through said first diode.

8. The apparatus according to any one of claims 1 to 7, further comprising a fluorescent lamp having first and second electrodes, said fluorescent lamp being electrically connected to said feeding and switching means.

9. Variable output fluorescent lighting apparatus substantially as herein described with reference to the accompanying drawings.

10. All novel features and combinations thereof.