US2429415A

US2429415A - Circuit for electric discharge devices

Info

Publication number: US2429415A
Application number: US598121A
Authority: US
Inventors: Lemmers Eugene
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1945-06-07
Filing date: 1945-06-07
Publication date: 1947-10-21
Anticipated expiration: 1964-10-21

Description

Oct. 215 1947. LEMMERS 2,429,415

CIRCUIT FOR ELECTRIC DISCHARGE DEVICES I Filed June 7, 1945 [/v TURZ' EUGENE LEM/WERE.

H/s ATTUPNEY Patented Get. 21, 1947 CIRCUIT FOR ELECTRIC DISCHARGE DEVICES Eugene Lemmers, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application June 7, 1945, Serial No. 598,121

4 Claims.

This invention relates to circuits for electric discharge devices, and especially to resonant starting circuits. The invention is useful for fluorescent lamps of the usual low pressure positive column type, as well as for other discharge lamps. Important objects of the invention are to provide higher voltage for starting the discharge than in subsequent operation, and to assure proper preheat of the discharge electrodes or cathodes before starting. The invention also aims to avoid high current surges that might injure lamps at starting, as well as substantial power losses during operation. The invention obviates the liability to premature starting of a discharge between cold or insufficiently heated cathodes, owing to erratic high voltage transients across resonant circuits at the instant of switching on, which largely depend on the point of the A. C. voltage cycle where switching on occurs. Other features and advantages of the invention will appear from the description of species and forms of embodiment, and from the drawings.

In the drawings, Figs. 1 and 2 are diagrammatic illustrations of discharge lamps with lead and lag circuits embodying the invention in simple forms, and Figs. 3 and 4 illustrate modifications of the starting circuit.

Figs. 1 and 2 each show a low pressure positive column discharge lamp l consisting of an envelope tube equipped with widely spaced cooperating

electrodes

2, 2 in its opposite ends. Either or each of the

electrodes

2, 2 may be a thermionic activated cathode embodying an electric heater for bringing it to a temperature of electron emission before the discharge between the electrodes is initiated. For instance, the

electrodes

2, 2 may consist of tungsten filament wires, in coil or coiled coil form, charged or coated with activating alkaline earth oxides, such as a mixture including barium and strontium oxides. The envelope I may contain an atmosphere of gas or vapor or both at low pressure: e. g., an inert rare starting gas, like argon at 2 to 6 mm. of mercury, and a supply of mercury that is indicated by a droplet 3. Also, an internal coating of luminescent material or phosphor 4 excitable by the radiation from the discharge is indicated on the envelope wall.

As shown, the

electrodes

2, 2 are connected to opposite sides of a discharge circuit which may be energized from any suitable A. C. source, such as a 110 volt cycle lighting circuit (not shown), and may include the usual inductive ballast 6, as well as a control switch I. A starting circuit 8 is shown connected across the discharge circuit 5 in parallel with the discharge device I, between and through the

cathode resistances

2, 2. In the case of'a lead circuit, Fig. 1, a capacitor or condenser 9 may be included in one side of the discharge circuit in series with the discharge device; or in the case of a lag circuit, Fig. 2, in the starting circuit 8 that is in parallel with the discharge device I.

In accordance with my invention, I include in the starting circuit 8 an inductance l0 and a resistance device or resistor l l, in series with one another. The value of the inductance 6 (and that of the capacitor 9, when in circuit 5) are so chosen that during operation the desired discharge current and a voltage less than the supply voltage on the circuit 5 are maintained across the

electrode gap

2, 2 of the discharge device I. The value of the inductance l0 (and that of the capacitor 9 when in the circuit 8) is then chosen so that with a low or zero resistance value for resistor II, the circuit 5 with its inductance 6 and the circuit 8 with its inductance l0 together constitute a resonant circuit in which the voltage across the

electrode gap

2, 2 exceeds the supply voltage on the circuit 5 and the break-down voltage of the lamp I When cold (or at ordinary room temperature of some 20 C'.), the resistor II has a resistance so high that the combined

circuit

5, 8 shows very little resonance; but this resistor II has a fairly large negative temperature resistance coefficient, and is so proportioned as to be heated by the current through it to a temperature at which its resistance becomes inconsiderable during a length of time not less than that required for the current to heat up the oathodes to a temperature of adequate electron emission, or perhaps slightly exceeding this. Resistors of these characteristics are commercially available, and may be of the type comprising carborundum or silicon carbide. Of course a resistance device of like characteristics but heated by a separate resistance or other heater might be used.

When the

circuits

5, 8 are first energized by closing the control switch I, the circuit resistance 3 due to resistor I l is so high that very little effective resonance exists in the combined circuit. By virtue of the high resistance of resistance II at this time and the consequent low current which flows in the starting circuit 8, the inductive re- 5 actance of inductance I0 is high so that the combined reactances of inductances 6 and ill is substantially greater than the capacitive reactance of capacitance 9. As the resistor ll heats up and its resistance decreases, the current in the com- 10

bined circuit

5, 8 increases, and likewise the Q of this

circuit

5, 8 inasmuch as the increased current flowing in the circuit reduces the inductive reactance of inductance l0 until there is enough resonance to give a Voltage exceeding the break-- down voltage of the lamp I, whereupon the discharge starts and becomes established in the lamp. The discharge once established, the effective impedance of the lamp l becomes less than that of the circuit 8, and the resistor I I cools ofi, resulting in a progressive, cumulative increase of the circuit 8 impedance and resistance, and in reduction of the current in this circuit. Thisvire tual removal of the inductance l0 from across the lamp l increases the efficiency of the circuit as a whole.

For the convenience of those i'wishing to use -my invention, I"will now. give illustrative values of circuit constants suitable for an ordinary commercial 15 Watt positive column fluorescent lamp 1 of usual 18' inch tube length and 1 inch diam- .eter; but these-are not to be understood as definingbr limiting tl'ie'invention in its broader aspects.

.In the case of the lead circuit of Fig. 1, the in- '3 ductances fi and 'lfl mayeach be wound to give 'a 160 voltdrop on a '60 cycle -A. Cficurrent of 0.330 amp. R. M. S., with a D50. resistance of 20 ohms or less; the capacitor 9 maybe*a3 microfa'rad condenser;'the resistance ll may have a cold nc-current value of 200'ohms at room In the case ofthe lag'c'ircuitof Fig. 2, the values of the circuit constants maybe the same except 5 for the inductance 6,'which' may be wound to give alOO volt drop on a 60 cycle A. C. current of 0.330

"Fig. 3"illustrates the adaptation' ofthe*Fig. 1

lamps I, I connected in series across the discharge circuit 5, andea'ch shuntedwith a starting circuit-8 or 8'-'includin g an inductance ill or ID.

As shown, only-oneof the starting circuits B,- 8

includes a resistor l l.

circuits to a'plu'rality of discharge devices or' Fig.4 illustrates another adaptation of theFig.

-1 circuits to a plurality 5 of discharge *devices or lam'ps l, I connected in series across the discharge circuit 5. Here a's'ingle starting circuit with one another shunts the serially connected lamps I, I, Provision for flow of current to preheatthejadjacent'cathodes 2, 2 of the lamps l, l

is made by connecting these cathodes into a heatto the startingcircuit'B bymeans of a coil [3 which coacts as secondary with the coil of the inductance ID as primary, andmay be wound on' the same core.

'B incIuding inductance 'Ifland resistor II in series ing circuit loop.l2 'which is inductively coupled In Figs. 2,'3,"and'4, various parts and features are marked with the same reference numerals as those corresponding in Fig. 1, as a means of dispensing with repetitive description-a distinctive prime being added where such distinction seems desirable.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination with an alternating current supply circuit, an electric discharge circuit embodying inductive ballast, an electric discharge device employing an ionizable medium and having eletrodes connected across sai'd' 'discharge circuit,-at least one of said='electrodes--being thermionic and embodying electric heating means connected to the corresponding side of said dischargecircuit, and a starting circuit connected 5 across said discharge circuit through said heating means, of an indutance and a current-heated electric resistance device of negative temperature resistance coefiicient serially connected in said starting circuit; and capacitance also included in the combined discharge and starting circuit, whereby the same is rendered resonant after said device heats up.

2. Ihe combination with an alternating current supply circuit, an electric discharge circuit embodying inductive ballast, an electric discharge device employing an ionizable medium and having thermionic activated refractory wire coils circuit correlated with said inductive ballast to form a resonant circuit afiording a discharge initiating voltage across the discharge device when the discharge circuit is energized, and a serially connected electric resistance in said starting circuit having when cold arelatively high value, suific'i'ent to substantially nullify the combined circuit resonance, and having such heat capacity and such a negative temperature resistance coefificient as to heat up and substantially lose its resistance by the time .currentfiow through said coils brings them to emissive temperature, whereby the resonance-becomes effective to initiate discharge.

3. In combination, an alternating current supply circuit, an electric dischargedevice-Of the type employing an ionizable medium-and having at least one" electrode of the filamentary type, a discharge circuit connected between electrodes of 'saiddischarge device and said supply circuit and including an inductive ballast,'a starting circuit connected acrossele'c'trodes of said device and comprising-aninductance and a serially connected resistance having-a negative temperature resistance coefiicient, and a capacitance connected in circuit with said discharge circuit and said start- -ting circuit, the value of said resistance at start- -ing being-such that the inductive reactance of said inductancerenders the combined starting and discharge circuit non-resonant and the subrelatively high voltage is impressed across said electrodes to initiate an arc discharge in said .device after the electrode has assumed a safe operating temperature.

4. In combination, an alternating current supply circuit, an electric discharge device of the type employing an ionizable medium and having at least one electrode of the filamentary type, a discharge circuit connected between electrodes of said discharge device and said supply circuit and including an inductive ballast, a starting circuit connected across electrodes of said device and comprising an inductance and a serially connected resistance having a negative temperature resistance coefficient, and a capacitance connected in series with said discharge and said starting circuits, said resistance controlling said inductance upon the flow of current therethrough to render said starting and discharge circuits resonant so that a relatively high voltage is impressed across said electrodes to initiate an are discharge in said device after the electrode has assumed a safe operating temperature.

EUGENE LEMME'RS.

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

UNITED STATES PATENTS 10 Number Name Date 2,170,447 Edwards (a) Aug. 22, 1939 2,170,448 Edwards (b) Aug. 22, 1939 2,284,407 Edwards (0) May 26, 1942 2,231,999 Gustin Feb. 18, 1941 15 2,351,499 Freeman June 13, 1944