US2503845A - Circuits for the oeration of fluorescent lamps - Google Patents

Description

April 11, 1950 J. SALPETER CIRCUITS FOR THE OPERATION OF FLUORESCENT LAMPS Filed July 23, 1946 DISC/I/IRGE r055 DISC/IA TUBE DISC/MEGA r055 sum van nor JAKOB LFIB SALPETER IN VEN TOR.

ATIORNFKI' fiatented Apr. 11, 1950 CIRCUITS FOR THE OPERATION OF FLUORESCENT LAMPS Jakob Leib Salpeter, Sydney, New South Wales, Australia, assignor to Hartford National Bank & Trust Company, Hartford, Conn as trustee Application July 23, 1946, Serial .No. 685,582 In Australia May 24, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires May v24, 1965 4 Claims. 1

The present invention relates to circuits for the operation of fluorescent lamps.

It is an advantage of cold cathode fluorescent lamps, as compared with hot cathode fluorescent lamps, that they can be satisfactorily operated with currents of two or more different values. For example the user of the lamp can operate it so that it passes a current of 60 milliamperes, or 190 milliamperes and so on to provide for different degrees of illumination. Sometimes more, sometimes less, artificial light is required, for instance, when artificial light is used to supplement natural light. The possibility of being able to alter the current (and accordingly the i11umi nation) constitutes a convenience and a saving.

Cold cathode lamps, as a rule, are energized by transformers, and thus it is relatively easy to provide various tappings on the secondary winding of the transformer in order to obtain the various currents. Moreover, the cold cathodes are usually of a rugged construction and do not unduly sufier if they are over energized or under energized. If the cathode of a hot cathode lamp is either over energized or under energized, however, the useful life of the cathode will be shortened. For this reason, hot cathode lamps are invariably operated at one rated current value only and if a lower or higher level of artificial illumination is required this may be achieved by employing a relatively large number of lamps and switching the individual lamps on or off according to requirements. This cannot be done very well, however, if the total number of lamps installed is small, as for example, in the case of desk lamps.

Another reason why it is desirable to be able to alter the value of the current supplied to a hot cathode lamp is that hot cathode lamps are usually designed for a higher current density than cold cathode lamps. The current density controls the temperature rise of the lamp bulb above the room temperature. The bulb temperature in turn controls the mercury vapour pressure within the tube. It is well known that there is, for every lamp design, some optimummercury vapour pressure which yields the maximum efl'iciency. If the ambient temperature is too high, the mercury vapour pressure will be too high and the efllclency will be less than that anticipated. A similar adverse result obtains if the ambient temperature is too low. This could be partly remedied if the current could be adjusted in accordance with the ambient temperature; lower currents with higher ambient temperatures, higher currents with lower ambient temperatures.

This invention seeks to overcome the disadvantages before referred to and, for that purpose, contemplates a circuit for altering the value of the current supplied to a hot cathode lamp without excessively shortening the life of the lamp. The invention is based on the discovery that it is not so much the higher operating current as the excessive starting current which affects the life of the cathode and accordingly the life of the lamp. The essential feature of the invention is the provision of a ballast comprising a variable inductance whereby difierent values of current may be supplied to the lamp to vary the brilliance of the lamp, the ballast being connected in circuit between the lamps and the supply means in such manner that the starting current is maintained at a substantially constant value.

Taking a watt fluorescent lamp as an example, the rated current for such a lamp is 410 milliamperes. It is proposed to make the ballast for three values of current i. e. 300, 400, .and 500 milliamperes but for one starting value of current only (for instance 600 milliamperes) it has been found that, in this example, the lamp life .(at 300 or 500 milliamperes) would be shortened by not more than 10-15% which is practically negligible, considering the advantages obtained from under energization or over energization. Under energization saves current and improves the lumen maintenance of the lamp. The light output of a fluorescent lamp decreases with time and the rate of that decrease depends on the current density; it will be lower with the smaller current. Over energization gives more illumination from the same number of lamps and improves the efiiciency (lumens per watt) of the lamp if the reason for over energization is a too low ambient temperature. In some cases, it might be found necessary to be satisfied with a poorer lumen maintenance if, for instance, the lamp were to be over energized at all times) The ballast according to the invention is connected in series with the lamp to the alternating current mains. Connected in parallel with he The current will then flow through the ballast and the lamp (but no longer throughthe cathodes and the starter switch). Since the" lamp voltage is much higher than the sum of the voltages across the cathodes when the starter switch is in its closed position, the operating current will be smaller than the starting current;

According to one specific manner of carrying the invention into efiect, the ballast consists of a plurality of inductances wound on a single core as shown in the accompanying drawings.

Referring now to the circuit diagrams, shown in the drawings Figure 1 illustrates one circuit for the operation of a fluorescent lamp. In this circuit the current from the mains flows via the windings 4 and 3, to the cathode 5, thence to the cathode I and back to the mains. The reference numeral 6 indicates the starting switch. In this particular circuit the current through the lamp for starting and during operation is controlled by the inductance of the windings 3'and 4 and the values of the starting and operating current will be the same as in the conventional circuit, i. e. 410 milliamperes and approximately 60! milliamperes respectively.

Figure 2 shows a further circuit in which the current for starting flows through the windings '4, 3 and 2 and also through the winding i but when the lamp is started the current through the lamp flows through the windings 4, 3 and 2 only. By connecting the winding i so that its field isin opposition to thefields of the windings ll, 3 and 2, and determining the number of its turns in such a manner that the windings I and 2 I cancel each other, a starting current of substantially the same value as in the circuit of Figure 1 is obtained while the operating current is smaller due to the additional impedance introduced by the winding 2, e. g. 300 milliamperes.

In the circuit shown in Figure 3 the current ing operation is larger, e. g. 500 milliamperes.

A switch may be employed to enable any one of the foregoing circuits to be selected as desired thus permitting the brilliance of the lamp to be varied but maintaining a substantially constant starting current.

Referring now .to Fig. 4, there is shown a starting and operating circuit for a fluorescent lamp, said circuit including a selector switch 8 consisting of five ganged units each having three operating contact positions A, B, and C. The arrangement is such that when'selector switch 8 is at position A the circuit is connected as shown in Fig. 1, when at position B the circuit is connected as in Fig. 2 and when at position C, the circuit is connected as in Fig. 3. Thus the starting current of the lamp is substantially the same for'each position of selector switch 8 whereas the operat- 1 ing current of the lamp and hence the brilliance thereof is different at each switch position.

Having now described my invention, what I claim as new and desire to secure by Letters Pat ent is:

1. A starting and operating circuit for a gaseous electric discharge device having two hot cathodes, said circuit comprising a current source for said device, first and second inductances, a starter switch, and switching means for Selec- :tively in one position connecting said first inductance, said second inductance, one of said cathodes, said starter switch and the other of said cathodes serially in the order named to said source and inanother position connecting said first inductance, one of said cathodes, said second inductance, said starter switch and the other of said cathodes serially in the order named to Said source, whereby the starting current of said device is substantially the same for both of said positions whereas the operating current is different.

2. A starting and operating circuit for a gaseous electric discharge, device having two hot cathodes, said circuit comprising a current source for said device, a first inductance, 'a'second inductance, a third inductance having a pair of windings, a starter switch, and'switching means for selectively in a first position connectingsaid first inductance, said second inductance, one of said cathodes, said switch and the otherof said cathodes serially in the order named to said source, in a second position connecting said first inductance. one of sai'd'cathodes,.said second inductance, said switch, and the other. of said cathodes serially inthe-order named r tofisaid source and in a third position" connecting said first inductance, said'seco'nd inductance, one" of said windings, one of said cathodes, said switch, the other of said windings and the other of said cathodesserially in the order named to said source, said one winding being connected in field opposition to said otherwindingywhereby the starting current for said device is substantially the same in all. three positions whereas the operating current'is 'difierent.

3. A starting and operating circuit for a gaseous electric discharge device having two hot cathodes, said circuit comprising a current source for said device, an inductor having a common core and first, second, third and fourth windings, said third and fourth windings having substantially equal inductance, a starter switch, and switching means for selectively in a first position connecting said first winding, said second winding, one of said cathodes; 'said switch and the other of said cathodes serially in the order'named to said source, a second'position connecting said first winding, one-"of said cathodes said second winding, said switch and the other {of said cathodes serially in the: dra :narned tosaid source and in a, third position connectin aid first winding, said second'winding, said third winding, one of said ca tho c 1es, v said switch, said fourth winding and theothe'riof said oath.- odes serially in theorder named to said source, said fourth winding being connected in fieldopposition to the remaining windings, whereby the starting current for said device is substantially the same in all three positions whereas the operating current is different. v -y -4.;A starting and;operating -circuitfor a gas;-

eous electric discharge device" having two-jhot cathodes said circuit comprising. a currentsource 6 for said device, an inductor having a common REFERENCES CITED core and first, second, third and fourth windings, The following references are of record in the said third and fourth windings having substanfile of this p tially equal inductance, and a starter switch, said first winding being connected in series with said 5 UNITED STATES PATENTS second winding, said third winding, one of said Number Name Date cathodes, said switch, said fourth winding and 1,930,123 Ewest Oct 10, 1933 the other of said cathodes to said source in the 2,056643 Zecher Oct 6 1936 order named, said fourth winding being con- 2,264,055 Stocker 25, 1941 nected in field opposition to the remaining wind- 10 313 72 n May 4, 1943 i 2,349,012 Spaeth May 16, 1944 JAKOB LEIB SALPETER. 2,392,845 Foerste Jan. 15, 1946

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