Display panels

Abstract

 A display panel 1 has a window 6 in a cover 4 illuminated oppositely of a viewer by a pair of fluorescent lamps 10 and 11. The display can be used, for example, to back-­light a transparency 8 slotted into the window 6 and supported by a frame 7. A pair of inverters 12 and 13 mounted upon a base 2 supply the fluorescent lamps 10 and 11 respectively with the power necessary to light each lamp 10, 11 and maintain each lamp 10, 11 lit.

Description

Technical Field

[0001] The invention relates to display panels, and particularly to display panels for back lighting transparencies. Back lit transparencies are used in, for example, advertising displays.

Background Art

[0002] Display panels, or light boxes as they are also commonly known, are used for a number of tasks. Display panels usually consist of a transparent surface which is lit from behind or from a side of the surface opposite to the viewer. The display panels can be used, for example, either to identify defects in textile materials, illuminate a drawing for tracing, or back light a transparency to provide an illuminated picture.

[0003] Display fittings, such as lamps and display panels, have in the past been suspended from a network of vertically affixed cables, usually of metal. These cables may be electrified with, for example, 12 volts AC which enables the display fittings to tap power for lighting directly from the cable at the points of fixture of the display fitting.

[0004] The current conducted by the exposed cables could be hazardous and has to be restricted for obvious reasons, but this in turn restricts the power available to the display fittings.

[0005] Conventional display panels have been illuminated by standard incandescent filament lamps, dichroic lamps, and the like. Such lamps tend to be bulky, and require the display panel to have a substantial depth in order to provide a diffuse light for illumination of the transparency. Fluorescent strip lamps are preferred as they generally provide a more diffuse light, but the combination of a fluorescent strip lamp and its requisite starter can also tend to be bulky.

The Invention

[0006] The invention provides a display panel comprising a mounting for a fluorescent lamp, and an inverter for supplying from a low voltage source the power necessary to light the lamp and to maintain the lamp lit.

[0007] More than one lamp may be mounted in the display panel, depending upon the requirements of the display. It is usual, but not essential, for each lamp to be powered by an idividual inverter.

[0008] The display panel is preferably suspended between a network of cables. The cables may be electrified, and tapped by the display panel as the source of power.

[0009] The inverter preferably comprises a time controlled switch, a relay operated by the time controlled switch, an oscillator to drive the centre tapped primary coil of a step-up transformer and to produce an alternating voltage output at the secondary coil of the transformer, and an inductance connected by the relay in parallel with the primary coil of the transformer to increase the frequency and magnitude of the voltage output at the secondary coil of the transformer to a level sufficient to light the fluorescent lamp.

[0010] If the cables are to be electrified with alternating current, then the inventer further preferably comprises a rectifier.

[0011] The inverter eliminates the need for each fluorescent lamp to have its own starter, as is conventional.

The Drawings

[0012] 

Figure 1 is an exploded view of a display panel according to the invention; and,

Figure 2 is a circuit diagram of an inverter for a display panel according to the invention.

Best Mode

[0013] With reference to Figure 1, the display panel indicated generally at 1 has a base 2 upon which a cover 4 seats. The cover 4 has in its upper surface a window 6 into which a pane of transparent material 8, such as a transparency, can be slotted. The transparency 8 is slotted through an opening 9 in the cover 4, and supported by a frame 7 surrounding the window 6.

[0014] Mountings for a pair of compact fluorescent strip lamps 10, 11 are affixed to the base 2 behind the window 6. Each of the lamps 10 and 11 is powered by an inverter 12 and 13 respectively, also affixed to the base 2. The lamps 10 and 11 illuminate the transparency 8 from behind. The inside of the panel should be white, or an opaque window pane (not shown) provided to diffuse the light.

[0015] The display panel 1 is suspended whilst in use from a pair of cables 16, one of which is shown. Base grips 18 and 20, mounted on the cable 16, grip the base 2 to the cable 16. The cable 16 and hence the base grips 18 and 20 are electrified to 12 volts AC. One cable grip 18 on each side of the board 12 is in direct contact with a conducting plate 14 on the board 2. Power for the display panel is tapped from the base grip 18 through the conducting plate 14 and supplied to each of the inverters 12 and 13 connected in parallel.

[0016] The edge 22 of the cover 4 is tailored to accomodate the base grips 18 and 20, and to conceal the region of contact between the base grip 18 and the conducting plate 14.

[0017] Figure 2 is a circuit diagram of the inverters 12 and 13 shown in Figure 1. Each inventer 12, 13 consists of a rectifier 24; a timed switch 26; a relay 30, 32; a pair of transistors 34, 36; and a step-up transformer 38.

[0018] The AC voltage fed by the conducting plate 14 is rectified to a suitable DC voltage, typically 17 volts.

[0019] The timed switch 26, at the heart of which is a 555 timer integrated circuit, operates the relay coil 30. On the introduction of power to the circuit, the timed switch 26 assumes an on state and the relay 30 becomes energised. This on state is resumed for only a limited duration subsequent to the introduction of power, and after a time predetermined by the resistance and capacitance values of the components connected to the 555 timer, the timed switch 26 switches off and the relay coil 30 is de-energised. Electrolytic capacitor 261 smooths the DC output from the rectifier 24. Resistor 262 and capacitor 263 control the triggering input, typically 15.5V, to the 555 timer. Resistor 264 and electrolytic capacitor 265 determine the duration of energisation of the relay coil 30.

[0020] The transistors 34 and 36 are alternately driven as an oscillator to produce an alternating current in the centre tapped primary coil 40 of the transformer 38, and hence an alternating voltage at the output of the secondary coil 42. This output voltage is supplied to each of the lamps 10, 11, typically 990 volts RMS. The transistors 34 and 36 are connected to a second primary coil 41 of the transformer 38 and self oscillate. Resistor 341 is a base drive resistor. Inductor L1 blocks AC signals passing back from the primary coil 40 of the transformer 38.

[0021] An inductor 44 is introduced in parallel with the primary coil 40 of the transformer 38 to alter the tuning of the primary coil 40 and to provide conditions sufficient to light the fluorescent lamp 10, 11 connected to the secondary coil 42. The introduction of the inductor 44 is controlled by the contact of the relay 32, which as explained previously is controlled by the timed switch 26, and the energisation of the coil 30. The introduction of the inductor 44 has the effect of increasing the magnitude and frequency of the voltage induced in the secondary coil of the transformer 42. The magnitude and frequency of the voltage is increased to a level and for a duration, controlled by the timed switch 26, sufficient to light the respective fluorescent lamp 10, 11. Capacitors 46 and 48 isolate the fluorescent lamps 10, 11 from the inverter circuit, that is, they block any DC signals.

Claims

1. A display panel comprising a mounting (2) for at least one fluorescent lamp (10,11), and CHARACTERISED BY having at least one inverter (12, 13) for supplying from a low voltage source the power necessary to light each lamp (10, 11) and maintain each lamp (10, 11) lit.

2. A display panel according to claim 1 wherein each fluorescent lamp (10, 11) has an individual inverter (12, 13) for supplying the necessary power.

3. A display panel according to claim 1 or claim 2 wherein each inverter (12, 13) has a time controlled switch (26), a relay (30, 32) operated by the time controlled switch (26), an oscillator (34, 36) to drive the centre tapped primary coil (40) of a step-up transformer (38) and to produce an alternating voltage output at the secondary coil (42) of the transformer (38), and an inductance (44) connected by the relay (32) in parallel with the primary coil (40) of the transformer (38) to increase the frequency and magnitude of the voltage output at the secondary coil (42) of the transformer (38) to a level sufficient to light the fluorescent lamp (10,11).

4. A display panel according to claim 3 wherein the oscillator (34, 36) is self oscillating.

5. A display panel according to claim 3 or claim 4 wherein the inverter has a rectifier (24) for the supply to the inverter (12, 13).

6. A display panel according to any preceding claim for suspension between electrified cables (16) which are tapped by the display panel as the supply to each inverter (12, 13.

Drawing