GB2104319A - Fluorescent lamp starter apparatus - Google Patents

Abstract

To provide a high voltage starting impulse to fluorescent lamp 10 without the use of a transformer in the circuit, the starter circuit comprises a voltage doubling and rectifying circuit including capacitors denoted by prefix C and diodes denoted by prefix D connected in series and parallel with the AC input. Resistor R1 dampens the input current and thus protects diodes D1 and D2 from damage, resistor R2 prevents excessive build up of voltage across the lamp 10 which might damage the lamp 10 and resistor R3 provides a current sink to speed extinction of the lamp when the current is switched off. Once lit, the lowered impedance of the lamp lowers the output voltage of the circuit. <IMAGE>

Description

SPECIFICATION Fluorescent lamp starter apparatus This invention relates to starter apparatus for a fluorescent lamp, for example a low-pressure mercury vapour lamp.

A fluorescent lamp usually comprises a tube, coated internally with a fluorescent substance and filled with a gas, for example mercury vapour, and two electrodes, one at each end of the tube, capable of emitting electrons. The electrons collide with atoms of gas causing them to emit radiation which strikes the fluorescent substance and causes the tube to light up.

Conventionally, a small heating filament is located at each end of the tube adjacent the respective electrode. When the filament is heated by application of an electric current, it promotes an increase in the emission of electrons over and above that brought about by the application of a voltage across the electrodes. The fluorescent lamp circuit also includes a choke or starter and a cut-out mechanism or stator. In order to initiate discharge in the fluorescent lamp, a high voltage surge must be generated by the starter and stator by means of a transformer located in the circuit. After such a high voltage surge has initiated the discharge, the voltage across the lamp must be lowered to its normal operating voltage by the starter and stator and the current in the heating filament must be immediately extinguished.The necessity for this sequence of operations is the reason why the usual method of lighting fluorescent lamps is so slow.

The object of the present invention is to provide improved fluorescent lamp starter apparatus capable of receiving AC input, doubling and rectifying the voltage and providing a high voltage starting impulse to a fluorescent lamp, the voltage doubling being accomplished without the use of a transformer.

With this object in view, the present invention provides fluorescent lamp starter apparatus capable of receiving AC input, doubling and rectifying voltage and providing a high voltage starting impulse to a fluorescent lamp comprising a voltage doubling and rectifying circuit including at least one diode and at least one capacitor connected in series or parallel in which charging and discharging of the or each capacitor takes place through a diode to provide a high voltage starting impulse without the use of a transformer in the circuit.

The fluorescent lamp itself is conveniently in the form of a tube, although it may be of any other suitable shape or size. The material of the tube is advantageously glass, quartz or PVC, but any suitable material may be used, the only requirements being that it can be vacuum sealed as a lamp and that it will not deform or change shape at a temperature below 45"C. The lamp is filled with a gas which is capable of emitting light after being subjected to a high voltage starting impulse. Furthermore an electric terminal of any type is located at each end of the lamp, forming a connection with the respective electrode.

A suitable power supply for the fluorescent lamp starter apparatus of the invention is in the range 1 00-250V AC, and the electric current is determined by the wattage of the particular lamp.

The invention will be described futher, by way of explanation and example, with reference to the accompanying drawings in which: Figure 1 is a simple circuit diagram for assisting explanation of the theory behind the present invention; Figure 2 is a half wave rectification circuit diagram; Figure 3 is a half wave voltage doubling circuit diagram; Figure 4 is a full wave voltage doubling circuit diagram; Figure 5 is a circuit diagram for assisting explanation of the theory behind the fluorescent lamp starter apparatus according to the present invention; and Figure 6 is a circuit diagram of a practical embodiment of fluorescent lamp starter apparatus according to the present invention.

The theory lying behind the present invention will be explained with reference to Figs. 1 to 5.

Fig. 1 shows an A.C. circuit including two capacitors C1 and C2. The electric current, in this circuit may be considerable. Each capacitor changes the phase of the alternating voltage by delaying it for one quarter wave or 90 degrees. According to Ohm's law, the voltage drop between the circuit terminals equals the product of the electric current and the circuit resistance; namely E=lR (Formula 1) (voltage denoted by E is expressed in volts, current denoted by I is expressed in amps and resistance denoted by R expressed in ohms) This formula may be applied to a capacitor circuit such as that shown in Fig. 1, in which case a proportion of the circuit resistance which is due to the presence of a capacitor is called capacity resistance and denoted by Zc. The unit of the capacity resistance is also the ohm.

Zc = ~~~~~~~ 2"f.C In this formula, f represents cycies per second of alternating power and C represents capacitance of the capacitor, the units being Faradays. The expression 277f indicates the angular speed of the alternating power.When Ohm's law is applied to capacity resistance, Zc is used in place of R; thus, because E= IR and R = Ze then E= lZc and l= E = = 2sfCE (Formula 2) 1 - 2#fC By insertion of suitable values obtained from equipment known to control electric current passing through a fluorescent tube, for the parameters of Formula (2), it is possible to calculate a suitable capacitance value for the capacitor in the circuit as follows:: (As) I= 2"'rtE C=l 27rf E now I = 50mA = 0.05A f = 60Hz E = 1 iOV Therefore C= 0.5 2 x 3.14 x 60 x 110 = 1.2jtf Thus a suitable capacitor nas a capacitance value ot 1.2 to 1.5 tjf. It should also be durable against a maximum voltage of 1.4 x 11 or, tnat is 1 54V.

Fig. 2 shows a basic half wave rectification circuit. The diode D1 will allow current to pass in only one direction, for example it may let the negative half wave pass through and cut out the positive half wave so that tne output wave from the diode comprises a plurality of negative half waves with non-voltage periods between adjacent half waves. Thus negative direction current pulses pass through the remainder of the circuit. If the average value of input voltage is Ein-V, the highest value of voltage will be 0.45 Ein V vvhile the direct current output will be Ein 1.4 R and the average DC value Ein 0.45 R A uni-directional, puising output voltage as supplied by the aforesaid half wave rectifying circuit does not have widespread use. However, it is possible to reform this voltage so that instead of a series of puises, a smoother output is achieved. If the level of this reformed voltage could be doubled and applied between two electrodes, one at each end of a fluorescent lamp tube, it would be unnecessary to provide a heating filament adjacent each electrode as the high voltage DC applied to the electrodes would be sufficient to overcome the potential difference between the electrodes due to the insulating action of. the gas and initiate discharge of the lamp.

The present invention provides an electrical circuit which is capable of doubling the voltage without the use of a transformer and increasing the voltage between the two ends of a fluorescent lamp tube. Any type of conductor material may be sealed into the two ends of the lamp tube to form a connection with the electrodes to provide a high voltage starting impulse to the lamp. A heating filament is not required.

In general, there are two ways of achieving voltage doubling in a circuit, namely half wave and full wave voltage doubling. A simple method of half wave voltage doubling may be explained with reference to the circuit in Fig. 3 which includes a fluorescent lamp tube 1 0.

During the negative half cycle of the circuit input the electric current passes through diode D1 to capacitor C1 which charges to its peak voltage (the peak voltage of a sine wave input is 2V = 1 .4V). During the positive half cycle of the circuit input, when the right side of capacitor C1 is positive, the voltage of diode D1 inclines to the opposite direction and its voltage rises to the level of the right side of capacitor C1, that is two times the peak input voltage namely 2 x 1 .4V = 2.8V. At the same time, diode D2 conducts current to capacitor C2 which charges to approximately 2.8V while also providing negative load resistance RL.This type of half wave voltage doubling circuit has an output frequency equal to the input frequency and the rated voltage of capacitor C1 is 1 .4V while that of capacitor C2 is 2.8V.

A method of full wave voltage doubling may be explained with reference to the circuit shown in Fig. 4 which also includes a fluorescent lamp tube 10. The capacitors C1 and C2 of this circuit will each charge, discharge and charge again in the opposite direction, becoming alternatively positive and negative at half cycle intervals. The output voltage of these two capacitors connected in series may be 2.8V and its continuous wave frequency is two times the input voltage frequency. The rated voltage of each capacitor C1 and C2 is in this case 1 .4V. In comparison with the half wave voltage doubling circuit, this full wave voltage doubling circuit operates to adjust the voltage more rapidly and thus provides a continuous wave with smaller oscillations about the general level.Also the peak current output is determined by capacitors C1 and C2. The rated current of this circuit may be obtained by substituting appropriate values for the other parameters in Formula (2).

When assembling an electrical circuit in accordance with the present invention, it is necessary to calculate the value of the following three parameters: 1. The current of the fluorescent lamp (this depends on the wattage of the particular lamp and may be calculated using Formula (2)) 2. The rated voltage required to start the fluorescent lamp 3. The reduction in voltage between two circuit output terminals 11, 1 2 attached to two electrodes 13, 14 at the ends of the lamp 10 which is required immediately after the lamp starts to conduct to allow continued discharge of the lamp at its normal operating voltage level.

Before calculating these parameters accurately, a rough relationship between the current and voltage of the circuit may be given as follows: Wattage of required voltage for fluorescent lamp starting lamp 1 OW 308-465V (DC) voltage after required lamp conducts current 48V + 5% 50mA + 5% From the above figures, suitable values for the capacitance of capcitors C1 and C2 can be obtained from Formula (2), 1 = 21rfCE.

Referring now to the electrical circuit shown in Fig. 4, it should be understood that capacitors C1 and C2, not only play a very important role in charging and discharging alternately during the positive and negative half waves of the input voltage, but these two capacitors also control the current of the circuit.

The two diodes D1 and D2 are connected in series together with the two capacitors Cl and C2. However, because of the presence of junctions a and b diode D1 and capacitor C1 are also connected in parallel with diode D2 and capacitor C2. When the potential of the input voltage at a is a half cycle higher than the input voltage at b, the diode D2 conducts to capacitor C2 which becomes charged to its peak voltage and when the potential at b is higher than the potential at a, the diode D1 conducts to capacitor C1 which charges to its peak voltage.Capacitors C1 and C2 are connected in series with the output terminals so that the output voltage will be the sum of the input voltages to the capacitors, in this case two times the peak voltage (2 x 1.4 Ein).

Referring now to the circuit shown in Fig. 5, it follows from the above theory that the DC voltage at junctions a, b, c, d and N will be: a = Ein VDC b = 1 .4Ein VDC c = 2 x 1 .4Ein VDC d = 3 x 1 .4Ein VDC N=nX 1.4EinVDC The following conclusions can therefore be reached: 1 The voltage increase at each capacitor or between adjacent diodes in sequence is 1.4Ein.

2. The opposite direction voltages passed through each adjacent pair of diodes are added together, thereby increasing the voltage after each said pair to two times the maximum input voltage (2 x 1 .4Ein).

3. The voltage output from each capacitor is substantially equal to the voltage output at the next but one diode in the circuit.

It should be understood that the maximum current which the diodes used in the circuit can conduct should be two times the current required in the circuit and likewise the maximum voltage which the diodes can withstand should be twice the maximum voltage during operation of the circuit.

The level of current flowing through the circuit depends on the capacitors used in the circuit.

The current through capacitors C1 and C2 must be calculated with respect to the wattage of the particular fluorescent lamp used, in accordance with Formula 2. The capacitor C3 and the other capacitors in the circuit conventiently have a capacitance value of about 0. 1 to 0.47 tlf, (The use of 0.1 pif capacitors will still result in voltage doubling).

The purpose of the voltage doubling of the circuit is to light the fluorescent lamp without the use of a heating filment. However, after the initial high voltage surge, which causes the lamp to begin conducting current and thus begin emitting light, there must be a reduction in voltage so that the lamp continues its discharge, that is it's light emission, at a lower normal operating voltage. Before the fluorescent lamp tube begins conducting current, its resistance value in the circuit is infinitely high so that no current flows through the lamp. There is, therefore, substantially no load within the circuit as a whole so that a large potential difference rapidly builds up across the lamp between the output terminals of the voltage doubling circuit which are located at each end of the lamp.This high potential difference is extinguished when the lamp lights up because the gas molecules within the lamp tube then conduct current through the tube. Thus, the lamp tube resistance is reduced to a suitable operating level, according to Ohm's law as follows: V= IR V therefore P = - @ If the lamp wattage is 10W, then approximate value of the operating voltage and current are 48V and 50ma- therefore the resistance R of the lamp when operating is as follows: 48 R = - x 10 = 960 ohm 50 From the abovementioned basic theories, an actual operating circuit can be constructed. A diagram of an operating circuit is shown in Fig. 6.In this circuit, a resistor R1 is present to protect diodes D1 and D2, which transmit the input voltage to the capacitors, from any initial momentary shock caused by a rapid stream of current when the power to the circuit is switched on. Resistor P2 prevents the voltage across the lamp rising to such a high level that the fluorescent lamp 1 0 itself might be adversely affected. If the resistance of the terminals 11, 12 themselves are sufficiently high, the presence of a separate resistor such as R2 in the circuit is not required. When the circuit power is switched off, resistor P2 stops the discharge of the fluorescent lamp 1 0, the rcsistance of the lamp 10 then becomes infinite as current is no longer conducted through the lcmp 1 0. and the residual current in the voltage doubling circuit drains away through resistor r,

Claims (11)

1. Fluorescent @@@@ @@@@@@ @@@@@@@@@ of receiving AC input, doubling and rectifying voltage and providing a high voltage starting impulse to a fluorescent lamp comprising a voltage doubling and rectifying circuit including at least one diode and at least one capacitor connected in series or parallel in which charging and discharging of the or each capacitor takes place through a diode to provide a high voltage starting impulse without the use of a transformer in the circuit.

2. Fluorescent lamp starter apparatus as claimed in claim 1 in which a voltage doubling and rectifying circuit comprises first and second diodes and first and second capacitors connected in series and parallel such that when the potential of the voltage at a first junction located between the first and second diodes is a half cycle higher than the voltage at a second junction located between the first and second capacitors, the second diode conducts to the second capacitor which becomes charged to its peak voltage and when the potential of the voltage at the second junction is a half cycle higher than the voltage at the first junction, the first diode conducts to the first capacitor which also becomes charged to its peak voltage so that the voltage of an output terminal connected in series with the first and second capacitors is substantially equal to the sum of the peak voltages of the capacitors.

3. Florescent lamp starter apparatus as claimed in claim 1 or 2 in which output terminals of the voltage doubling and rectifying circuit are connected to two terminals sealed one into each end of the fluorescent lamp so that the voltage between the terminals is doubled by means of said current, without the use of a transformer, and the lamp is momentarily lit.

4. Fluoresecnt lamp starter apparatus as claimed in claim 1, 2 or 3 in which the peak voltage across each fully charged capacitor is substantially 1.4 times the input voltage.

5. Fluorescent lamp starter apparatus as claimed in any preceding claim in which the peak voltage across each diode is substantially 1.4 times the input voltage.

6. Fluorescent lamp starter apparatus as claimed in any preceding claim in which the components of the voltage doubling and rectifying circuit are arranged such that the sum of the opposite direction voltages passed through each diode will be substantially equal to two times the peak input voltage (1.4 times the average input voltage).

7. Fluorescent lamp starter apparatus as claimed in any preceding claim in which the voltage across each capacitor is substantially equal to the voltage across the next but one diode.

8. Fluorescent lamp starter apparatus as claimed in any preceding claim in which the voltage doubling and rectifying circuit includes negligible resistance to the passage of current so that the potential difference between the output terminals of the circuit is high until discharge of the lamp, located between said terminals, commences when the lamp immediately conducts current yet retains sufficient internal resistance to lower the voltage to a suitable value for normal functioning.

9. Fluorescent lamp starter apparatus as claimed in any preceding claim in which the fluorescent lamp is a tube.

10. Fluorescent lamp starter apparatus as claimed in any preceding claim in which the fluorescent lamp is of glass, quartz or PVC.

11. Fluoresecent lamp starter apparatus as claimed in any preceding claim in which the material of the fluorescent lamp does not deform below a temperature of 45"C.

1 2. Fluorescent lamp starter apparatus as claimed in any preceding claim in which the fluorescent lamp is filled with a gas which is capable of emitting light after being subjected to a high voltage starting impulse.

1 3. Fluorescent lamp starter apparatus substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.