US2620459A - Discharge lamp circuit - Google Patents

Description

Dec. 2, 1952 B. A. SAWYER ET AL 2,620,459

DISCHARGE LAMP CIRCUIT Filed Oct. 50, 1945 Brute A. jawyer Laurence Burns INVENTORS ATTO RN EY Patented Dec. 2, 1952 UNITED STATES PATENT OFFICE DISCHARGE LAMP CIRCUIT of Massachusetts Application October 30, 1945, Serial No. 625,586

1 Claim.

This invention relates to apparatus and circuits for operating electric discharge lamps, particularly those having a thermionic cathode.

Such lamps have previously been operated with relays to allow preheating of the filament, or directly from high voltage transformers without any preheating of the filament. The first method produced an undesirable lag in starting after applying voltage to the circuit, and the second produced low efiiciency because of the increased starting voltage. Our circuit avoids both these difficulties, and allows prompt starting without much loss in efficiency.

An advantage of our invention is the provision of a high electrode heating current for a very short time, and the reduction of this current to a low value on starting of the lamp.

This is attained by using an additional winding on the usual choke coil of the ballast, connecting this winding in series with the electrode heater, and proportioning and connecting this winding so that the voltage induced in it by the normal operating current of the lamp opposes the voltage of the source used for heating the electrode. I have referred to the electrode heater, but of course in most discharge lamps, the electrode will consist of a coiled oxide coated wire which will serve at once as electrode and heater.

Other objects, features and advantages of the invention will be apparent from a consideration of the following specification, taken in conjunction with the accompanying drawings.

Fig. l is a plan view of a core suitable for the magnetic circuit used in the invention; and

Fig. 2 is a schematic diagram of a circuit according to the invention.

In the latter figure, the lamps l and 2, which may be fluorescent lamps if desired, have the filamentary electrodes 3, 4, and 6, preferably of coiled tungsten wire coated with one or more of the alkaline earth oxides, one electrode being at each end of a lamp.

The filamentary electrodes 3, 4, 5 and 6 are connected, respectively to the heating windings l, 8, 9 and I0, through the auxiliary windings ll, [2, l3, M, respectively. The heating windings are on a transformer connected to the line, although any other suitable source of heating voltage may be used instead of such windings if desired. The auxiliary windings H, l2, I3, [4 may be on the same core as the usual choke coil or inductance forming all or part of the lamp ballast.

The primary winding I 5 is connected to the line and the secondary winding [6 is connected at one end to the choke coils I1, [8 leading to the lamps l, 2, and at the other end to one end of the primary IS in the usual auto-transformer manner, the other side of the power supply to the lamp being the other end of the primary 15, which end is connected to the electrodes 4 and 6 as the common return terminal.

The choke coil I1 is connected between one end of the autotransformer secondary l6 and the electrode 3, while the choke coil [8 is connected to the electrode 5 in the same manner, except that the condenser 19 is interposed in series between the choke coil [9 and the lamp 2 in the usual manner. The condenser may be of such a size that it places the two lamps suiiiciently out of phase to correct the power factor and reduce the stroboscopic effect from the pair of lamps. The .bleeder resistance 20 may be used across the condenser.

When the power is first applied to the circuit, the voltage from the heater windings i, 8, 9, it! will produce a heating current in the filaments 3, l, 5, 6. At this time there is no current through the lamp itself, that is across the discharge space between the electrodes 5 and 6, and 3 and 4, and hence no current through the choke coil ll. There is thus no counter voltage induced in the coils ll, 12, i3 and I4, and hence the flow of current in the filaments is not greatly reduced by these windings, although they will, of course, have a small impedance.

As soon as the filaments become sufiiciently heated to emit enough electrons :to allow the lamps to start, current will flow in the choke coils I! and I8, producing a counter-Voltage in the coils H, l2, l3, 14, which should be so proportioned as to balance out, as far as ossible, the voltage of the heater windings l, 8, 9, Hi, thus insuring that the current to the filaments 3, 4, 5, 6, drops to a low value. Difference in phase may prevent complete balancing out of the current.

In order to make each lamp as independent as possible of the other, the windings ll, I2 are preferably on the same core 21 as the choke H, and the windings l3 and M on the same core 22 as the choke [8.

The transformer core 23 will ordinarily be separate from the choke core, although parts of their cores may be common as shown in Fig. 1, which shows an arrangement suitable for the invention. In Fig. 1, the transformer core 23 may have the transformer windings 7, 8, 9, It, IS and I6 wound thereon in the usual manner, the core only being shown for clarity. The magnetic circuit will be closed by arms 24, 25, 26 and 2?. The transformers may have as low leakage reactance as the construction permits.

The core 2| will have the coils H, M, 2 wound thereon and the core 22 the coils it, Hi and E8. The cores 2! and 22 are closed to the transformer core 24, 28 by the pieces 32, 23, 29, 39, 3! and 33 through the short air gaps 34, 35, 36, 31, 38 and 39. The core portions 24 and 26 thus act as a common path for the transformer and a choke, but the remainder of the paths are separate. The metal piece, preferably non-magnetic, helps to align the core and hold it in position. The screws 4i and 42 may pass through the piece 45, the core, and a similar piece to 40 on the other side of the transformer, to be held by threads on a nut on said other side.

The flux from both the transformers and one of the choke coils flows through arms 24 and 26 of the core shown in Fig. 1. Accordingly, if the filament heating windings 1, 8, 9, are wound on these legs 24 and 26, they will supply voltage from the transformer flux to the filaments, prior to the starting of the lamp, and if the choke coil windings are connected with their polarities such that the choke coil flux passes through legs 24 and 26 in a direction opposite to that of the transformer flux, the total flux passing through the coil, will be reduced, with consequent reduction in the voltage supplied to the heater, once the lamp starts and current passes through the choke windings. The reduction may be made sumcient to drop the filament current to a low value once the lamp starts, without requiring the counter-voltage coils l I, l2, 13, Hi. However, placing coils on the legs 24 and 25 makes the stacking of the core laminations a more complicated process. In addition, reduction of the heating current by the countervoltage coils i more readily controlled and allows the coils I, 8, l3 and [4 to be wound directly on leg 23 with the other transformer windings.

When the heating current is to be reduced by the interaction of choke and transformer flux, the two heating coils on each of" the legs 24 and 25 are preferably arranged symmetrically, so that one coil is on the portion of the legs 24 and 26 between legs 23 and 25 and another on the portion between legs 23 and 21.

In order to reduce the maximum transformer voltage necessary to start the lamp under all conditions, a film of moisture-dispersing material is preferably used on the lamps. Without this coating on the lamps, a much larger starting voltage must be provided by the transformer, despite the fact that it will not be necessary to start the lamps under the majority of conditions.

Although we have described a two lamp circuit for convenience, my device is obviously applicable to a single lamp circuit also, and the circuit of Fig. 1 will of course function if one lamp is omitted, for example, if one lamp reaches the end of 4 its life. The circuit can, of course, be used with as many lamps as desired.

What we claim is:

A lighting circuit comprising: a discharge lamp having two preheatable filamentary electrodes each of said electrodes having two terminals; a transformer having a main secondary and having auxiliary secondaries for supplying heating current to each of said filamentary electrodes, said auxiliary secondaries being separate from each other and from said main secondary; a reactor having a main coil separate from each of said main and auxiliary secondaries and connected in series with said main secondary and said discharge lamp, connections to the lamp being made to one terminal of each electrode; secondary windings on said reactor, each of said secondary windings being separate from each other and from the main and auxiliary secondaries and from the main coil of the reactor, each of secondary windings on said reactor being connected in series-opposing relationship with one of said auxiliary secondaries of said transformer to produce a counter voltage to the voltage of the auxiliary secondary when current flows through the lamp and the main coil of said reactor, one such auxiliary secondary of said transformer and one such secondary winding on said reactor being connected in series with the two terminals of one of the filamentary electrodes of said lamp, the other of said auxiliary secondaries of the transformer and the other of said secondary windings of said reactor being connected in series with th two terminals of the other of said filamentary electrodes, thereby reducing the current through said electrodes when current flows through the lamp and the reactance coil.

BRUCE A. SAWYER.

LAURENCE BURNS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES General Elec. Review, Aug. 1944, pgs. 6-16.

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