Display circuit

A discharge tube opening circuit for varying tube intensity at regular intervals without flicker between an illuminated and an unilluminated state. Combinations of tubes controlled by respective circuits give rise to novel display arrangements through choice of tube colors and particular sequences of variation of luminous intensity.

FIELD OF THE INVENTION 
THIS INVENTION relates to a means and a method for operating discharge 
tubes and to displays utilising discharge tubes operated according to the 
method. 
BACKGROUND OF THE INVENTION 
Generally, in order to continuously vary the intensity of a light source in 
a display environment, an incandescent source is employed to which a 
variable voltage supply is connected. The use of these devices in displays 
causes a problem for the display's designer in that considerable amounts 
of heat generated by the incandescent lamps utilised therein must be taken 
into account in making the design. The heat generated by incandescent 
lamps must be dissipated otherwise overheating occurs and lamps burn out. 
The problems associated with incandescent lamps are largely avoided by 
adopting light sources such as fluorescent tubes. Fluorescent tubes 
present problems because of flicker when coming on such as to impair their 
usefulness in a continuously varying display where the flicker destroys 
the aesthetics of the display and introduce cost penalties in providing 
components needed for their ignition and control. It is known to 
continuously vary the intensity of a fluorescent tube over a range of 
intensities, but flicker free operation from a switched off condition is 
another problem. As a result, fluorescent tubes have not found application 
in displays to the same extent as incandescent sources whose intensity is 
readily and simply variable, and neon tubes which may be switched on 
without flicker, but are normally operable in a steadily more intense 
regime built up from a switched off condition. 
SUMMARY OF THE INVENTION 
The present invention enables the operation of gas discharge lamps, such as 
fluorescent and neon tubes, in an operative regime wherein the tubes may 
be controlled with a continuously varied output intensity to provide 
useful displays. 
An object of the invention is a means whereby the intensity of a discharge 
tube may be continuously varied. Another object of the invention is a 
display device which may employ a combination of colored discharge tubes 
each individually operated by a means for flicker free switching and 
continuous intensity control whereby a continuous range of color effects 
may be generated using the combination of discharge tubes. Other objects 
and advantages of the invention will hereinafter become apparent. 
The invention achieves its advantages through provision of a discharge tube 
circuit arrangement for operation of at least one discharge tube 
comprising a power supply circuit to fire at least one discharge tube, 
said power supply circuit including means operable to vary the power 
supply to the tube in accordance with a control signal, at least one 
control signal generating circuit for supplying said control signal to 
said power supply circuit, said control signal generating circuit having 
an input and circuit means to generate a predetermined control signal in 
response to a switching signal applied to said input, said predetermined 
control signal varying progressively to thereby cause the power supply 
circuit to progressively vary the power supplied to the tube between a low 
luminance level and a high level, and programming means to provide a 
predetermined pattern of switching signals to said input.

DETAILED DESCRIPTION 
In the embodiment of FIG. 1 power from a supply 10 is fed to discharge 
tubes, in this case to fluorescent tubes 11 by a power supply circuit 
employing conventional means such as ballast coils 12 with power to each 
tube under the control of a gate controlled switch 18 provided one to each 
tube. The actual on time of switch 18 during each cycle of the supply is 
set by a program circuit 15 which outputs a signal on line 16 at times set 
by the connections of the circuit 15. Circuit 15, in this embodiment 
comprises a pair of master/slave flip-flops such as the 7473 driven by a 
clocking device formed by a standard timer such as the 555. Control signal 
generating circuit 17, on receipt of a signal on line 16, using an RC 
combination, causes switch 18 to progressively input more power to its 
fluorescent tube to raise it from a non-luminous standby mode to full 
illumination. After an appropriate period, the reverse of this process is 
initiated and the tube is returned to a standby, non-luminous mode. Power 
to the integrated circuits and the switch circuits is supplied by sub 
circuits 13. Circuit 17 is duplicated for each of the switches 18 and the 
tubes 11 are fired in a preset sequence with each powering on and off to 
provide a varying display should tubes of, for example, different colors 
be employed. 
In the figure three fluorescent tubes are controlled by a solid state 
switching element to produce flicker free operation throughout a range of 
operating intensities. Control of the switching elements provides a 
gradual build up of power to the fluorescent tubes to a maximum operating 
level with the program circuit 15 to determine the on/off sequence of the 
three fluorescent tubes. Standard integrated timers such as the common 555 
may be used in conjunction with master/slave flip-flops such as the 7473 
and these can provide the necessary time control to achieve a sequential 
switching on and off of the fluorescent tubes to provide a particular 
display sequence. 
The power supply circuit 13 provides two outputs. One is filtered by a 220 
microfarad capacitor to provide a steady 20 V positive DC supply and the 
other is an unfiltered 20 V positive DC supply having a 100 Hertz 
frequency. The filtered supply is fed to a shunt regulator comprising a 
dropping resistor and a 5.1 V zener diode. This circuit provides the 5 
volt DC supply for the integrated circuits used in the circuit. 
The 555 timer I.C. of subcircuit 14 provides an astable multivibrator. The 
frequency of oscillation is determined by the value of the capacitor from 
pin 2 of the I.C. to ground and the resistors between pin 6&7 and 7&8. 
The 7473 dual J K flip flop I.C. of program circuit 15, in addition to the 
diode logic array, provides sequentially one of three output signals to 
subcircuit 16. The circuit is clocked by the square wave output of 
subcircuit 14. 
Subcircuit 16 comprises a buffer stage and a resistor, capacitor network. 
The buffer stage converts the 5 volt logic signal from the subcircuit 15 
to an inverted 20 volt signal. This signal is applied to the R C network. 
The charge, discharge rates are governed by the values of the two 
resistors and the capacitor. The diode following the network isolates the 
R C network from influences of the following subcircuit (17). 
Subcircuit 19 provides a pulse shaper producing pulses which correspond to 
the zero cross-over point of the sinusoidal input AC waveform from the 
mains supply. This pulse is fed to subcircuit 17. 
Subcircuit 17 is a pulse stretching or modulating circuit. The incoming 
voltage from subcircuit 16 varies the pulse width of the signal provided 
from subcircuit 19. The last transistor in this section is fed pulsed DC 
collector volts so as to provide a trigger voltage used to switch the 
triac every half cycle of the AC volts applied to the triac. 
Once the voltage of the collector of the transistor rises above 0 volts, 
the triac of subcircuit 18 switches on and the base signal applied to this 
transistor is used to switch off the transistor (thus the triac) after the 
time duration of the pulse determined by the preceeding circuitry. 
In the switching subcircuit 18 triacs are switched on for a variable length 
of time thus providing a path to neutral from the fluorescent tube for the 
AC power. The variable pulse duration reduces the effective power supplied 
to the tube. 
The ballast coils 12 provides a current limiter once the fluorescent tubes 
have initially struck. 
The filament windings keep the inert gas in the tube ionised so as not to 
have the tube flash on application of power to the tube. 
The circuit of FIG. 1 enables the progressive lighting of a luminiscent 
panel in front of said tubes with each tube switched to a luminous state 
from a non-luminous standby condition in which the tube has sufficient 
power applied to it to maintain it in its fired state, with a gradual 
build up of intensity to full power, and a gradual drop off thereafter to 
the non-luminous standby state after preset times at the full power or low 
power condition. 
The circuit of FIG. 1 when employed with a combination of three different 
colored fluorescent tubes may be used to operate the tubes behind a 
luminiscent panel carrying a transparency, such as an outdoor scene so as 
to light the transparency in a manner simulating the night, day light 
variations which would be observed in real life. Thus night, dawn, day, 
sunset and dusk may be continuously reproduced in a large optical display 
carrying an outdoor scene in transparency form. The changes of 
illumination may be preset to take the scene through the day/night cycle 
in any particular timed pattern. 
The circuit of FIG. 1 might be used with any combination of fluorescent 
tube colors and display panel to produce a timed sequence of vari-coloured 
illumination levels at the discretion of the display's designer. A black 
light tube might also be employed to cause fluorescence of areas in the 
luminiscent panel located on the display, either on the transparency or a 
separate transparency added in overlay to that carrying the rest of the 
displayed material. Using different colored fluorescent tubes behind 
overlaid transparencies, each carrying differently colored presentations 
corresponding to the different fluorescent tubes, may allow different ones 
of the overlays to be separately highlighted to produce further novel 
display effects. 
The display of the invention envisages the timed sequencing of the 
switching of a fluorescent tube to different power levels in either a 
stepped sequence of luminous levels or continuous variations of levels. 
Additional tubes may be combined to give further variations on the range 
of intensity levels which might be produced and to add in the possibility 
of varying the color of the display as the tubes are powered in varying 
sequences. Thus a wide range of hitherto unknown lighting sequences are 
obtained to provide back lit display panels with, for example, luminiscent 
surfaces lit from behind with one or more transparencies formed in the 
luminiscent surface. Additionally, a number of overlaid transparencies may 
be employed to achieve a desired display layout. 
In the circuit of FIG. 1, the discharge tubes are fluorescent tubes. 
Described below is how the above circuit may be also employed so as to 
operate neon tubes. 
In FIG. 2 the circuit is modified to suit the power requirements of neon 
tubes. The operation of the circuit is as above set out in respect of 
fluorescent tubes and like parts are like numbered. 
In the embodiment of FIG. 2 power from a supply 10 is fed to discharge tube 
21 in this case a neon tube by a power supply circuit employing 
conventional means such as step up transformer 20 with power to the tube 
21 under the control of a gate controlled switch 18 one switch being 
provided for each tube. The actual on time of switch 18 during each cycle 
of the supply is set by a pulse generator 19 via a pulse width modulator 
in control signal generating circuit 17 associated with each switch 18. 
The signal generating circuit 17 receives a varying signal under control 
of program circuit 15 which outputs a signal to subcircuit 16 at times set 
by the connections of the circuit. Program circuit 15 in this embodiment 
comprises a pair of master/slave flip-flops such as the 7473 driven by a 
clocking device formed by a standard timer such as the 555. Control signal 
generating circuit 17, on receipt of a signal from subcircuit 16, using an 
RC combination, causes triac switch subcircuit 18 to progressively input 
more or less power to its discharge tube to raise it from a non-luminous 
state to full illumination or vice versa. Power to the integrated circuits 
and the switch circuits is supplied by sub circuits 13. The circuits 17, 
each being duplicated for each of the subcircuit switches 18 for a 
plurality of tubes only one of which is shown in FIG. 2, fires their tubes 
in a preset sequence with each powering on and off of the individual 
circuits 17 to provide a varying display should tubes of, for example, 
different colours be employed. 
As with the embodiment of FIG. 1, the circuit of FIG. 2 enables the 
progressive lighting of a luminiscent panel in front of said tubes with 
each tube switched to a luminous state from a non-luminous condition, with 
a gradual build up of intensity to full power, and a gradual drop off 
thereafter to the non-luminous state after preset times at the full power 
or low power condition. 
The circuit of FIG. 2 when employed with a combination of three different 
colored discharge tubes may be used to operate the tubes behind a 
luminiscent panel carrying a transparency, such as an outdoor scene so as 
to light the transparency in a manner simulating the night, day light 
variations which would be observed in real life. Thus, night, dawn, day, 
sunset and dusk may be continuously reproduced in a large optical display 
carrying an outdoor scene in transparency form. The changes of 
illumination may be preset to take the scene through the day/night cycle 
in any particular timed pattern. 
While the above has been given by way of illustrative example, many 
modifications and variations as would be apparent to persons skilled in 
the art may be made thereto without departing from the broad scope and 
ambit of the invention as herein set forth and defined in the following 
claims.