WO1988007316A1

WO1988007316A1 - Activating lighted signs

Info

Publication number: WO1988007316A1
Application number: PCT/AU1988/000070
Authority: WO
Inventors: Berni Ford
Original assignee: Berni Ford
Priority date: 1987-03-17
Filing date: 1988-03-17
Publication date: 1988-09-22

Abstract

An activation circuit for gas discharge tubes (12) having a step-up transformer (11) with low level DC power applied to a centre tap (13) to the primary winding, power being switched (14, 15) alternately into the two arms of the primary winding to provide a high frequency, high voltage level on the secondary that powers the discharge tube (12). Switching of power into the primary winding is achieved by using transistorised switches (14, 15), in particular, transistor pairs, switched by a pulse train generated by a square wave oscillator (19).

Description

Title: "ACTIVATING LIGHTED SIGNS" BACKGROUND OF THE INVENTION

(1) Field of the Invention

THIS INVENTION relates to circuits for the 5 activation of gas discharge tubes such as neon tubes and argon tubes that are commonly used in providing lighted signs and other lighted displays.

(2) Prior Art

Neon signs and lighting are generally such

10 that they may only be practicably operated by connection to mains power so as to be able to draw sufficient power to maintain the sign in an activated state. Neon glass tube, typically 15 mm tubing, is generally connected to a step-up transformer which has a capacity on the

15 primary side of 240 volts with the secondary at 15,000 volts to 24,000 volts working on 50 Hz. A transformer of this size will in effect drive approximately 50 lineal feet of neon tubing. Because of the amount of electricity required to operate this system, it has not

20 been advisable or economical to use any other medium of supply other than mains power.

It would be desirable in remote areas, etc., to be able to use alternate sources of power such as batteries, solar panels, etc. 25 SUMMARY OF THE PRESENT INVENTION

It is an object of this invention to provide neon and other like tube based displays, lighting, and the like, that may be operated off lower DC voltages such as that which is supplied by batteries and solar

30 panels.

Other objects, and various advantages, will hereinafter become apparent.

The present invention achieves its objects by provision of a circuit for the activation of a gas

35 discharge tube such as a neon tube or an argon tube which circuit comprises: a transformer with primary and secondary windings thereto; the secondary winding being connected, in 5 use^ to the gas discharge tube to provide power thereto; characterized in that there is provided: a means for chopping a DC voltage supply that is connected across the primary winding; and the primary winding being wound and 10 connected in a push-pull configuration.

The chopping means may achieve its function in a number of ways. Chopping may be accomplished by feed back from extra windings on the transformer. Chopping may be accomplished by a fixed oscillating 15 source (i.e. crystal, TTL logic, 555 timer, etc.) used to switch the supply at frequencies of 1000 Hz and upwards.

The circuit of this invention may be connected up to a variety of power supplies. It can be powered 20 from solar panels, in combination with a battery backup, from batteries alone, or from a rectified AC source such as standard mains power. Use of the invention can effect substantial power savings. Roof top signs may be powered from roof top solar panels with batteries or 25 mains backup thereto.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to a preferred embodiment as shown in the accompanying drawings, in which: 3.0 FIG. 1 is a diagram illustrating general requirements of the invention; and

FIG. 2 is a circuit diagram illustrating a particular embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED 35 EMBODIMENTS In FIG. 1, power to activate a gas discharge tube such as a neon tube, or an argon tube 12,- is fed from the secondary winding of transformer 11 via a transmission line 10. The secondary winding receives power from a primary winding that is fed with power from a low voltage source applied to centre tap 13. The primary winding is operated in a push-pull manner with transistor pairs 14 and 15 performing the necessary switching. The transistor pairs are controlled by out of phase pulse trains on lines 16 and 17, which pulse trains may be produced by a phase splitter 18 operating on a square wave output of oscillator 19. The oscillator 19 may be stabilised by being powered from a stabilised regulator 20. The regulator and transistor pairs are powered off a power rail 21 which is connected to the low voltage source.

The above described circuit may be used to light long lengths of neon tubing, or tubing filled with other gases, with or without mercury, for the purpose of display signs and lighting. The circuit enables the neon tube to run off a direct current source, from 1.5 volts and upwards. Typically, 24 volts is used. The circuit enables deployment of a device which facilitates the lighting of signs in remote regions which county councils do not service; and the use of batteries/solar- cell combinations provide a source of direct current. The lighting may be provided wherever existing systems are in operation, as well as areas where conventional power is not available by use of batteries and/or solar panels.

The device works by chopping the direct current and passing it through a primary winding of a step-up transformer, while applying the output generated in the secondary winding to the terminals of a neon tube. In the above described circuit, a fixed oscillator based upon a 555 Timer may be used to generate an output of about 20,000 Hz. Use of a feed back arrangement is less desirable due to the frequency drift which is inherent with that type of arrangement. As the load increases, the frequency falls. This is an undesirable effect. To ensure further stability of the oscillator, its power supply might be accurately regulated. A 555 Timer based oscillator provides a square wave output which the splitter can use to generate two outputs, one in phase with the timer output, and one with an opposite phase. These two outputs may then drive the switching circuits to effect the chopping action at the primary windings of the transformer. The pair of switches are alternatively on and off, with one on while the other is off. The same effect can be achieved using a single switch (transistor pair as in FIG. 1) with a single primary winding, however, this would use nearly twice as much current (a commodity which there is not much of in battery/solar- cell arrangements) and hence the push-pull method has been chosen.

Using the above described arrangement, a solar powered low voltage neon sign or lighting system is possible. A solar panel may be coupled to a battery storage device with a 1.5 volts and upwards output. The low voltage arrangement is effective to activate long lengths of neon tubing, or tubing filled with other rare gases, with or without mercury. The present system may be used wherever the mains supply is not available, or too costly to install, e.g. on top of multi-storey buildings, shopping centres, etc. The battery storage bank may be charged in a number of different ways. The batteries might be charged regularly through the means of a battery charger as an alternative to a solar array. The circuit may be operated off the battery at all times or selectively so, being powered off a mains supply to the battery charger, the battery bank being a standby for times when the mains supply fails. In FIG. 2, power to activate tube 12, is fed from transformer 11 via7 in use, high voltage coaxial cables for example. The primary winding is powered off supply line 21 from, typically, a 24 volt source at a centre tap 13. Transistor pairs 14 and 15 sequentially switch the primary windings in a push-pull manner. Timer 19 outputs a square wave pulse train that operates directly on switch 15 via line 17 and transistor 22 is connected to introduce a phase delay on line 16 to switch the transistor pairs 14 on when pairs 15 are off and vice versa. A fuse 22 may be used to protect the circuit from overload and resistor 24 provides the requisite voltage for operation of the standard 555 Timer circuit. In the circuit of FIG. 2, the 555 Timer operates at 20 KHz. The transistors 2N3055 are mounted to a heat sink and a fan may be included within the circuit housing to improve cooling. The transformer primary comprises 6 turns with 3,000 turns on the secondary, the coils being about a ferrite core with a 1 mm air gap. This circuit is suited to tubes of neon, argon or mixtures of both.

Whilst the above has been described with reference to a preferred embodiment, it will be clear that many modifications and variations as would occur to those skilled in the art may be made thereto within the spirit and scope of the invention defined in the appended claims.

Claims

1. A circuit for the activation of a gas discharge tube such as a neon tube or an argon tube which circuit comprises: a transformer with primary and secondary windings thereto; the secondary winding being connected, in use, to the gas discharge tube to provide power thereto; characterized in that there is provided: a means for chopping a DC voltage supply that is connected across the primary winding; and the primary winding being wound and connected in a push-pull configuration.

2. A circuit as claimed in Claim 1 wherein: the means for chopping the DC supply comprises a switch in series with each arm of the primary winding, the switches being triggered alternately to apply the supply voltage to each arm in turn.

3. A circuit as claimed in Claim 2 wherein: the switches are transistor pairs triggered by out of phas pulse trains.

4. A circuit as claimed in Claim 3 wherein: the pulse trains are generated by a square wave oscillator and a phase splitter acting on the output thereof.

5. A circuit as claimed in Claim 4 wherein: the square wave oscillator comprises a timer switching a supply thereto on and off at a preset frequency.

6. A circuit as claimed in Claim 5 wherein: a transistor is connected between the output of the square wave oscillator and one of the switches to the primary winding to cause a phase delay of the pulse train fed thereto.

7. A circuit for the activation of a gas dishcarge tube wherein: the gas discharge tube is connected across the secondary winding of a step-up transformer; the primary winding of the step-up transformer is centre tapped and each arm created thereby has power that is applied to the centre tap switched, in use, by a switching transistor; characterized in that the transistor switches are sequentially operated by out of phase pulse trains of a preselected frequency.

8. A circuit as claimed in Claim 7 wherein: the pulse trains are generated from the output of a timer circuit that regularly switches a voltage at its output on and off at the preselected frequency, the output thereof being fed directly to one transistor switch without delay, and to the other with a phase delay.

9. A circuit as claimed in Claim 8 wherein: the phase delay is created by a transistor interposed between the timer circuit and the second transistor switch.

10. A circuit for activation of a gas discharge tube wherein: the gas discharge tube is connected across the secondary winding of a step-up transformer; the primary winding of the step-up transformer is centre tapped and each arm created thereby has power that is applied to the centre tap, in use, switched alternately thereto; the primary windings are alternately switched by a switching means in series therewith; characterized in that the switching means is sequentially operated by out of phase pulse trains at a preselected frequency, the pulse trains being generated from the output of a timing circuit operated regularly to switch a DC voltage level on and off to generate a pulse train.