GB2195843A - Energy transformation apparatus - Google Patents

Abstract

Apparatus for transforming electrical energy into another non-heat, non-kinetic energy form, comprises a high Q resonant circuit loop containing a static energy transformation device in the form of a chemical cell or a discharge lamp and a pulse generator for generating electrical pulses at a repetition rate corresponding to the fundamental resonant frequency of said loop. In a circuit for reactivating primary cells or recharging secondary cells, an integrated circuit timer 11 drives the resonant loop 18 via a transformer 17 the secondary winding of which forms the inductive elements of the loop. When a diode 19 is forward biased, the inherent capacitance of the cell 21 is the predominant capacitance of the loop 18 and determines the fundamental resonant frequency, whereas the capacitance of the diode 19 predominates, when it is reverse biased and the circuit 18 rings with a damped oscillation at a higher frequency. Adjustable elements 12, 13, 15 allow the frequency, mark/space ratio, and amplitude of the energising pulses to be altered. In an alternative charger, the transformer forms part of a blocking oscillator (Fig. 3). A discharge lamps drive circuit (Fig. 4) may also use a blocking oscillator, the resonant loop capacitance being determined by the capacitance of the lamp (61) before a plasma forms therein. The oscillator may receive a D.C. supply from an A.C. to D.C. converter having a phase controlled triac (42) for adjustment of the supply voltage. <IMAGE>

Description

SPECIFICATION Energy transformation apparatus Background of the Invention This invention concerns static energy transformation apparatus for transforming electrical energy supplied from a conventional source into another non-heat, non-kinetic form. Such energy transforming apparatus may be considered to include chemical cells wherein electrical energy is used to perform an energy absorbing reaction which may be reversed at will at a later time so as to provide regenerated electricity. It will also include discharging tubes such as fluorescent lamps wherein the electrical energy is transformed into light energy the output of which is its only purpose.

Discussion of the Prior Art It is known, for example, for U.S. specification 3,609,502 (Birkett et al) and British Patent specification 1578922 (McFarlane et al) to provide apparatus for re-charging secondary cells by means of high frequency pulses which are applied to the cell in a controlled manner throughout- the re-charging process. Such apparatus may include fixed frequency oscillators or clock generators for -generating the pulses at the required rate and induction means for inducing pulses of energy into the charging circuit. Apparatus for reactivating primary cells is also known, for example, from EP-A-0047183 in which unidirectionally controlled pulses of current at 100 Hz are applied to the battery with progressively increasing mark-space ratio from its discharged condition to its charged condition.

In discharge tube energising circuits it is common practice to operate some tubes at a higher voltage than normal mains voltage and sometimes also at a higher frequency than the mains frequency. An example of the use of a higer frequency source is the case of the commercially available- battery operated lamps having fluorescent tubes.

High Q electrical circuits have their normal application in the fields of communications and related equipments utilising electromagnetic radiation in the detecting or conveying of information. Energy is consumed of course in the function of such equipments and some of this energy is converted into electromagnetic radiation but the equipments have primary functions other than that of producing transformed free or stored energy.

Discussion and Objects of the Present Invention The present invention depends on certain phenomena which occur, in relation to mediums containing free ions, only at very high values of voltages and/or currents which values are present in very high 0 circuits.

These effects bare very fundamental and are not fully understood but they are manifest by certain results which have been considered impossible to achieve up to the present.

Thus in the case of commercially available primary cells it is known from the prior art that limited reactivation is possible by a normal re-charging process but such re-charging can only occur once or twice before the cell becomes useless for its normal purposes.

Upon re-charging, it is found that the storage capacity of the cell is impaired and this impairment becomes progressively more pronounced the longer the re-charging proceeds. The chemical effect causing this impairment is described for example in U.S. specification 3,615,859 (Brook Schumn Jnr.) in column 4 lines 25-55 which describes a barrier which is formed at the interface between the so-called bobbin surrounding the cathode (positive electrode) and the electrolyte in typical zinc, ammonium-chloride, primary cell. The bobbin material is a depolariser which in this cell comprises a mixture of manganese dioxide and carbon. The barrier is actually a hard insoluble crystalline complex comprising Zn (NH3) C12 plus water of crystallisation.The water which goes into the crystals is extracted from the electrolyte, therefore, as the barrier forms the electrolyte becomes progressively more -dehydrated. At the anode electrons are removed from the zinc atoms as the zinc is dissolved into the electrolyte to form zinc chloride complexes. A reversal of current through the cell will cause the zinc in the electrolyte to be redeposited on the anode and this zinc is thus available to take part in further discharges of the cell. However, the crystalline barrier remains and is not broken down. Moreover, because the barrier increases the internal resistance of the cell, heat is generated during recharging which results in additional losses-of water from the electrolyte. Similar conditions will be found to occur with all other types of standard primary cells in current commercial use.

In the case of some secondary cells, particularly the standard lead-sulphuric acid cell, an insoluble crystalline compound is deposited over a period of time on one of the electrodes, thereby masking it. In the case of the lead acid cell this process is called sulphation because the crystalline substance is lead sulphate which is deposited on the cathode. The process is irreversible and progressive, so that such cells are considered as having finite lives after which they must be replaced. The condition usually arises long before such cells might have to be replaced for other causes, such as the mechanical disintegration of the electrodes.

It is now found that when the aforesaid primary and secondary cells are connected in a high Q circuit in series with a diode, having a polarity to provide re-charging and the circuit is pulsed with energy at the "resonant" fre quency of the circuit, then the relevant barrier, be it around the depolariser of the primary cell or that masking the cathode of the lead acid secondary cell, is progressively broken down.

In the case of the primary cell its re-charging capacity is restored to that of when the battery was new.

In the case of discharge tubes the high -vol- tages cause the electrons which are bound to the atoms of the gases to be shifted into higher energy states than would normally be achieved and strip more energy to be converted directly into photons than is normally the case. Thus the standard fluorescent tube connected in the high 0 circuit can be run from the mains supply with an improvement in overall circuit efficiency of around 50%.

With such tubes before striking occurs, the tube appears in the resonant circuit as a capacitance, the current flowing into the tube is limited by the circuit inductance therefore the circuit has a fundamental resonant frequency which is determined by the "capacitance" of the tube and the external inductance in the resonant circuit. Energy fed to the tube at a repetition rate corresponding to this frequency becomes stored- in the tube over the short period of each cycle of operation. During each such cycle of operation the gases ionise as the voltage builds up across the tube allowing current to flow with the increasing magnitude.

Eventually, with the increased voltage across the tube, the dielectric property of the gas filling breaks down and an arc strikes between the electrodes. The electrical current of the arc has a magnetic field associated with it and the tube therefore now appears to the circuit as an inductance. At this point the tube goes into a very high frequency oscillation during which it alternates between its capacitative condition and its inductive condition. During each of these high frequency swings a part of the energy of oscillation is transformed into light radiation. In this manner the oscillations are damped and eventually the stored energy is insufficient to sustain them. They then cease and the tube becomes non-conductive.

At this point the new pulse of energy is fed into the circuit and the process recommences.

Thus it is an object of the invention to provide apparatus, having a resonant frequency circuit, for the utilisation of energy and the transformation of such energy into an alternative non-heat form without any mass acceleration.

It is a further object of the invention to provide in said apparatus such a circuit having means for pulsing it at a frequency corresponding to the resonant frequency of a tank circuit having the equivalent capacitance and inductance of the said circuit.

It is a further object of this invention to provide a dry cell reactivator using such a circuit. It is yet a further object of the invention to provide a secondary cell re-charger using the aforesaid circuit. It is yet a further object of the invention to provide a drive circuit for a discharge tube utilising the said circuit.

In its broadest form the invention comprises electrical energy utilising apparatus for connection to a conventional electrical source comprising a resonant oscillating circuit loop containing a static energy transformation device for transforming electrical energy into another non-heat non-kinetic energy form, said loop exhibiting effective series inductance and capacitance and high Q characteristics during each cycle of operation, and a resonant frequency pulsing means for feeding pulses of energy into the loop at a repetition rate corresponding to the fundamental frequency of an equivalent tank circuit containing the values of inductance and capacitance of the loop, said energy transformation device essentially comprising a pair of spaced apart electrodes between which there is an energy transformation fluid medium, said medium being in intimate contact with at least one of said electrodes and said electrodes being connected electrically in said loop.

A further aspect of the invention comprises charging apparatus and primary cell reactivator for re-charging secondary and primary cells comprising a pair of terminals for connection to the cells to be charged or reactivated a circuit loop connected to said terminals, said loop incorporating inductance means and a unidirectional current means connected in series with the said cells, said unidirectional current means being connected with a polarity to permit direct current to flow therethrough only in the charging direction of the said cells, and pulsing means for pulsing the said loop with current pulses at a frequency substantially corresponding to the resonant frequency of a tank circuit having a inductor of equivalent value of inductance to the inductane of the loop and a capacitor having a capacitance equivalent in value to the dielectric capacitance exhibited by the cells in the circuit.

In a further aspect the invention comprises apparatus for energising a gas-filled discharge lamp comprising first and second terminals for connection respectively to electrodes at first and second ends of the discharge tube, a circuit loop connected to said terminals, said loop incorporating inductance means and pulsing means for pulsing the said loop with electrical pulses at a frequency substantially corresponding to the resonant frequency of a tank circuit having an inductor with an inductance of equal value to the inductance of the loop and a capacitor having a value of capacitance equal to the dielectric capacitance exhibited by the tube before a plasma is formed in the tube.

The novel features together with further objects and advantages will be better understood from the following description when considered in connection with the accompany ing drawings.

Brief Description of the Drawings Figure 1 shows a basic equivalent circuit of the embodiments of the invention described herein: Figure 2 shows a charging circuit for a primary or secondary cell: Figure 3 shows a charging circuit specifically for reactivating primary cells: and Figure 4 shows an energising circuit for a fluorescent lamp.

General Description of the Embodiments The basic equivalent circuit according to the device of the invention is shown in Fig. 1 in which a high Q closed loop circuit (2) includes a pulse generator (3) which pulses the circuit at a predetermined repetition rate corresponding to the resonant frequency of the loop. The pulse generator (3) draws energy from a conventional electrical power source (4) which in most cases will be a mains supply, but in some applications may comprise a low voltage supply or even a stored energy source. Circuit (2) also contains an energy utilisation and conversion device (5) which may be, for example, a chemical cell or a gas-filled discharge tube.

The circuit may also incorporate the unidirectional current device e.g. diode (6). Circuit (2) will have inductance which will normally be associated with the pulse generator and which may comprise the leakage reactance of a pulse transformer. The utilisation device will have inherent capacitance as will also any unidirectional device, more particularly in its blocked or reverse biased condition. By virtue of these reactances the circuit will have at least one resonant frequency mode and in some applications there may be several discrete resonant frequency modes, each being dependent upon the magnitude of the pulse excitation. The pulse generator delivers pulses of energy to the circuit at the resonant frequency. The tuning of the pulse generator may be manual or it may be made automatic by providing inductive feedback to an oscillator.

Chemical Cell Embodiments The embodiment illustrated in Fig. 2 comprises a battery charger (i.e. secondary cell charger), or a primary cell reactivator and is intended for relatively heavy duty applications, for example, re-charging batteries of many -ampere-hours capacity. Referring to the figure a standard type 555 integrated circuit counter (11) is connected as the pulse generator. The frequency of the operatipn is adjusted by the manual adjustment of a variable capacitor (12) connected thereto and the pulse mark/space ratio is adjusted by the manual setting of a potentiometer (13) also connected to the integrated counter circuit (11). Power is supplied to the circuit by a mains operated DC power pack of convention design.The output of the pulse generator is connected to a pulse shaping circuit comprising a Zenerdiode (14) in series with a potentiometer (15) and pulses of appropriate magnitude are fed to an integrated circuit power amplifier (16) which may be of any conventional type. A ferrite core pulse transformer (17) is connected at the output of the power amplifier. The resonant circuit loop (18) containing the battery (21) to be recharged or the cell to be reactivated is connected across the secondary winding of this transformer. The loop (18) includes a diode (19) and a current indicator (20).The frequency of operation (the fundamental resonant frequency) is of the order of 25-50 KHz and under resonant conditions the insoluble barrier formed at the electrolyte/polariser interface in the case of the zinc chloride primary cell and the insoluble sulphate barrier formed on the cathode of the secondary cell is broken down and is driven back into solution in the electrolyte as re-charging proceeds. This of course restores the water to the electrolyte that was previously bound up in the insoluble crystals.

The following operation is thought to occur.

During the half cycle of the resonant frequency in which the diode is forward biased, the build up of current in the charging circuit establishes a magnetic field in the ferrite core.

The inherent capacitance of the chemical cell connected to the circuit is the predominant capacitance and determines the fundamental frequency of operation. In the ensuing half- cycle the diode becomes back biased and in this condition it appears to the circuit as the predominating capacitor. The circuit therefore rings with a damped oscillation at a much higher frequency corresponding to the newvalue of capacitance in the circuit. In the next half cycle the diode becomes forward biased thereby "shorting out" its capacitance and the circuit enters a further sequence of events corresponding to the sequency described above. The ringing during the blocking half cycles of the diode cause the insoluble barrier referred to above to be broken down.

An inexpensive arrangement not requiring adjustment of any kind, which is suited for reactivating domestic type dry cells is illustrated in Fig. 3. This arrangement comprises a blocking oscillator circuit (22) which consists essentially of a transistor (23) having its base and collector inductively coupled through a ferrite core (24). The circuit (22) is coupled through the ferrite core (24) to the resonant circuit (25) and it is also connected to a standard DC power pack (26) operated from the mains supply from which it draws its energy.

The resonant circuit (25) comprises a winding (27) inductively coupling the ferrite core (24), a diode (28) shunted by a high value resistor (29), a current indicator (30) and the dry cell (31) which is being reactivated.

The reactances of the resonant circuit (25) are coupled back to the blocking oscillator circuit (22) and determine the frequency of operation thereof. When the diode (28) is biased in its forward direction the dry cell appears in the circuit as the predominant capacitance.

The resultant charging current causes a flux to be established in the ferrite core. When the diode (28) becomes back biased during the next half cycle of the operating frequency (which again will be of the order to 25-50 KHz) it then appears as the predominating capacitance of the circuit (25) and the latter rings with a damped oscillation at a very much higher frequency.

With the dry- cell disconnected, the blocking oscillator is free-running at a frequency determined predominantly by coupling between the windings (32) and (33) and the capacitor (34).

As shown in Fig. 3 the current indicator (30) is a solid state indicator comprising a lightemitting diode (35) shunted by a Zenerdiode (36).

Discharge Tube Applications -Every column of gas or mixture of gases has its own characteristic dielectric properties at a particular pressure, its own conductivity at this pressure before and during ionisation of the gas or gases, and its own inductive characteristic after electrical breakdown of the column; It also has its own transition time from the preionising state to the state in which total breakdown has occurred on application. of an ionising voltage to the column.

During this transition time the column is effectively an energy absorber and appears to its energising circuit as a capacitance. This period is therefore regarded as the capacitance phase of operations. After breakdown the column appears to the said circuit as an inductance because of the considerable current which flows in the arc. If energy is supplied to the column in pulses from a pulse generator with sufficient magnitude to cause breakdown, a very high frequency oscillation ringing effect occurs in which energy stored in the column appears to oscillate between the plasma of the column and the magnetic field associated with the arc.

During these oscillations very high voltages and currents are manifest within the gas column itself with the result that most of the energy of the oscillations is converted into electromagnetic radiation at wavelengths characterised by gas or gases of the column.

These oscillations cease when there is no longer sufficient energy to sustain the plasma.

The process operates most efficiently if the pulse repetition rate is adjusted so that no sooner has the plasma collapsed at the end of one of the said very high frequency oscillations than a further pulse of energy is delivered to the column and this may be most effectively achieved by adjusting the value of the external inductance of the energising circuit so that at this pulse repetition rate the circuit resonates. The pulse repetition rate may be varied by manually tuning the pulse generator or by means of frequency dependant feedback to an oscillator in the pulse generator. The capacitance of the resonant circuit is that provided by the gas column. This capacity characteristic is a dynamic one in that it appears to alter in steps as the magnitude of the excitation pulses increase. Corresponding steps are observed in the light output of the discharge tube.

When operating discharge tubes in accordance with the present teachings there is no requirement for the use of ballast chokes or resistors as in conventional discharge tube circuits. Moreover, the pulses will have a sufficiently high voltage to cause the column to ionise without the use of incandescent electrodes (as in standard fluorescent tubes) or auxiliary arcs or conventional starting devices (e.g. the glow tube starters in fluorescent tubes) which may be dispensed with. The resonant frequency is generally of the order of 100-200 KHz and consequently there is no observable flicker in the light emitted by the discharge tube.

It is found that as a consequence of the normal variation in the composition and partial pressures of the gas fillings of discharge tubes the characteristics of discharge tubes may vary both between individual tubes of the same kind and over a period of time (because of gas diffusion, etc.) it is necessary therefore to have some provision within the operating circuit for adjusting the frequency of operation of the pulse generator in order to maintain the operation of the circuit to its maximum efficiency. This adjustment may simply be a manually adjustable capacitor in the feedback of an oscillator or it may be made automatic by providing a suitable dependant feedback to a pulse generator. An example of circuit providing the latter operation is a blocking oscillator generally as hereinbefore described in relation to the reactivation of domestic type dry cells.

Details of an exemplary circuit are now described with reference to Fig. 4 of the accompanying drawings which is intended as the energising circuit of a standard mains operated fluorescent tube. The normal starter switch circuit is not required and has been omitted. It should be observed that because the operating conditions of the tube in this circuit are very different to the normal operation of the tube when connected to the mains supply, principally because of the very much higher voltages involved, the colour emission of the tube will be different from normal. Consequently, the tube phosphor coating should be selected accordingly, The circuit basically comprises a mains frequency controllable voltage power supply section (40), a blocking oscillator section (50), and the resonant circuit (60) containing the fluorescent tube (61).The power section consists of a mains isolation transformer (41) having on its primary side a TRIAC (42) with a controlled phase excitation circuit. The latter includes a DIAC (43) connected to the trigger electrode of the TRIAC and in series with a phase control circuit (44) comprising the components R1, R2, Rs, C1 and C2. R3 is made adjustable to enable the phase of the trigger voltage to be swung over a predetermined angle thereby controlling the period in each half cycle that the TRIAC conducts. On the isolated secondary side of the transformer the pulses of current provided by the TRIAC are fed into a full wave rectifying circuit (45) followed by a conventional L and C tuned filter (46). Except in the phase control circuit where power losses are insignicant there are no ohmic components in the power supply to cause power losses.

The smoothed DC is fed to the blocking oscillator section (50) which comprises a transistor (51) having a first winding (52) in series with a capacitor (C3) in its base and second winding (53) in its collector circuit whilst its emitter is connected directly to one side of DC supply. The first and second windings (52, 53) are inductively coupled by means of a ferrite core (53). A third winding (62) inductively coupled to the first and second windings, is connected directly to the electrodes of the discharge tube (61).

The resonant frequency of the resonant circuit consists of a range of discrete values which are dependant upon the magnitude of the direct voltage across the blocking oscillator. The preferred resonant frequency mode is of the order of 100-200 KHz. The frequency of self-oscillation of the discharge tube is of another order or so higher than this therefore such apparatus will need provision for Faraday screening if interference with other electrical equipment is to be sufficiently avoided. All the components illustrated in this circuit are conventional and commercially available and therefore are not described further herein.

It should be noted that with this circuit the absence of starter gear and ballast inductance and/or resistors compensates for the cost of the controlled power section, the two transformers, the blocking oscillator transistor and the other components, so that capital costs are somewhat similar. In the longer term, the tubes may be made more cheaply because the incandescent electrodes and the means for heating these electrodes are not required and therefore may be replaced by simple electrodes. For the reason that the incandescent electrodes are not depended upon, the life expectancy of the discharge tube is somewhat greater than when the tube is used in a conventional circuit.

Also, it should be observed that though the voltage on the electrodes is of such magnitude as to enable the gas content to be ionised without the need for heated incandescent electrodes, the average power delivered by the power supply section is very low, being much less than the normal power requirements of a fluorescent tube in the standard energising circuit; therefore the electrical shock which could be received upon accidental contact with the tube connections is limited to the amount of energy stored in the tuned filter which is very low and far below lethal values.

There is also added protection from the fact that the tube connections are isolated from the mains supply by the two transformers.

With suitable tapings on the secondary winding (62) and the addition of a diode (not shown) in the resonant circuit (60), this apparatus may alternatively be used to reactivate dry cells.

Claims (22)

1. Electrical energy utilising apparatus for connection to a conventional electrical source comprising a resonant oscillating circuit loop containing a static energy transformation device for transforming electrical energy into another non-heat non-kinetic energy form, said loop exhibiting effective series inductance and capacitance and high Q characteristics during each cycle of operation, and a resonant frequency pulsing means for feeding pulses of energy into the loop at a repetition rate corresponding to the fundamental frequency of an equivalent tank circuit containing the values of inductance and capacitance of the loop, said energy transformation device essentially comprising a pair of spaced apart electrodes between which there is an energy transformation fluid medium, said medium being in intimate contact with least one of said electrodes and said electrodes being connected electrically in said loop.

2. Apparatus as claimed in Claim 1, wherein said static energy transformation device is a primary cell and said loop includes a unidirectional device connected so as to allow current to flow through it in the charging direction relative to the cell.

3. Apparatus as claimed in Claim 2, wherein the primary cell is a dry cell.

4. Apparatus as claimed in Claim 3, wherein the dry cell is of zinc/ammonium-chloride type.

5. Apparatus as claimed in Claim 1, wherein said static energy transformation device is a secondary cell and the said loop includes a unidirectional device connected so as to allow current to flow through it in the charging direction relative to the cell.

6. Apparatus as claimed in Claim 5, wherein said secondary cell is a lead/acid cell.

7. Apparatus as claimed in Claim 6, * wherein said lead/acid cell is one of a series of interconnected cells contained in a common casing and together comprising a battery.

8. Apparatus according to Claim 1, wherein the static energy transformation de vice comprises a gas-filled discharge tube and said resonant frequency pulsing means deliv ers pulses at a repetition rate corresponding to the resonant frequency characteristic of the loop before a plasma forms in the tube, and the pulse having a voltage- magnitude corre sponding to the ionising potential of the col -umn of gas in the tube when the gas is at ambient temperature.

9. Apparatus according to Claim 8, wherein the gas-filled discharge tube has non incandescent electrodes.

10. Apparatus according to Claim 8, wherein the gas-filled discharge tube com prises a fluorescent tube.

11. Charging apparatus and primary cell re activator for re-charging secondary and pri mary cells comprising a pair of terminals for connection to the cells to be charged or reac tivated, a circuit loop connected to said termi nals, said loop incorporating inductance means and a unidirectional current means connected in series with the said cells, said unidirectional current means being connected with a polarity to permit direct current to flow therethrough only in the charging direction of the said cells, and pulsing means for pulsing the said loop with current pulses at a frequency substan tially corresponding to the resonant frequency of a tank circuit having an inductor of equiva lent value of inductance to the inductance of the loop and a capacitor having a capactance equivalent in value to the dielectric capactance exhibited by the cells in the circuit.

12. Charging apparatus as claimed in Claim 11. wherein the loop incorporates the secon dary winding of a ferrite cored transformer having a primary winding connected across the output of a controllable pulse generator.

13. Charging apparatus as claimed in Claim 12, wherein the pulse generator comprises an integrated circuit counter connected as an os cillator having manual frequency adjustment means connected to prescribed terminals thereof, pulse shaping means connected to the output of the counter and an integrated circuit power amplifier connected to the out put of the pulse shaping means for amplifying the power of the pulses, said power amplifier being connected to the said primary winding of the transformer.

14. Charging apparatus as claimed in Claim 13, wherein said integrated circuit counter incorporates means connected to prescribed ter finals thereof for adjusting the width of the pulses.

15. Charging apparatus as claimed in Claim 13, wherein said pulse shaping means incorporates controllable output means for controlling the magnitude of the pulses fed to the said power amplifier.

16. Apparatus for energising a gas-filled discharge tube comprising first and second terminals for connection respectively to electrodes at first and second ends of the discharge tube, a circuit loop connected to said terminals, said loop incorporating inductance means and pulsing means for pulsing the said loop with electrical pulses at a frequency substantially corresponding to the resonant frequency of a tank circuit having an inductor with an inductance of equal value to the inductance of the loop and a capacitor having a value of capacitance equal to the dielectric capacitance exhibited by the tube before a plasma is formed in the tube.

17. Apparatus as claimed in Claim 16, wherein said inductor comprises a secondary winding of a transformer having a split primary winding and said pulsing means comprising a transistor connected as a blocking oscillator and having a respective portion of the primary winding in each of its base and collector circuits, said apparatus further comprising a controllable voltage, direct current, power source connected to the pulsing means.

18. Apparatus as claimed in Claim 17, wherein said controllable voltage direct current power source comprises a transformer having a primary winding connected to a primary circuit and a secondary winding connected to a secondary circuit and said primary circuit containing a trigger operated phase controlled switch element connected between the mains supply and the primary winding of the resistor and said secondary circuit comprises a full wave rectifying circuit means and a smoothing circuit connected between the said full wave rectifying circuit and the pulsing means.

19. Apparatus as claimed in Claim 18 including means for varying the phase of a trigger for operating the controlled switch element.

20. Apparatus as claimed in Claim 16, wherein the said pulses having a voltage magnitude corresponding to the ionising potential of gas in the discharge tube when the gas is at ambient temperature.

21. Apparatus according to Claim 20, wherein the said gas-filled discharge tube is a fluorescent lamp.

22. Apparatus substantially as described herein with reference to the accompanying drawings.