US3479558A

US3479558A - High voltage arc discharge lamp with low voltage control circuit

Info

Publication number: US3479558A
Application number: US648346A
Authority: US
Inventors: Sandford C Peek
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1967-06-23
Filing date: 1967-06-23
Publication date: 1969-11-18
Anticipated expiration: 1986-11-18

Description

Nov..18, 1969 s. c. PEEK 3,479,558

HIGH VOLTAGE ARC DISCHARGE LAMP WITH LOW VOLTAGE CONTROL CIRCUIT Filed June 23, 1967 2 E1 :31 L 2 f" X j iii?! United States Patent 3,479,558 HIGH VOLTAGE ARC DISCHARGE LAMP WITH LOW VOLTAGE CONTROL CIRCUIT Sandford C. Peek, Ipswich, Mass., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed June 23, 1967, Ser. No. 648,346 Int. Cl. H05b 41/14 US. Cl. 315-98 4 Claims ABSTRACT OF THE DISCLOSURE An electronic circuit for applying periodic ionizing pulses and discharge current to a fluorescent lamp rated for operation from a 240 volt alternating current supply and having heated filaments, the circuit including a semiconductor valve for applying the pulses and rated for operation at 120 volts applied. A transformer whose primary is connected to the 240 volt supply, has secondaries for supplying heating current to the lamp filaments and also has a primary tap for supplying 120 volts to the semiconductor.

Conventional fluorescent lamp starting and operating circuits have comprised a ballast for applying a high starting voltage to the lamp to ionize it and start discharge and for inductively limiting current through the ionized lamp. Because of the weight and bulk of the ballast and its high expense, heating and noise, control circuits have been proposed which start and control the lamp discharge by various electronic switching circuits. Some of the advanced electronically valved circuits comprise pulse generating or gating semiconductor valve for periodically applying a voltage pulse to the lamp thereby ionizing the lamp sufliciently to support an arc discharge for a limited period, usually a half-cycle or less of the alternating current supply. Typically the electronic valve is connected in series with a pulse storage capacitor across the alternating current supply. Frequently the fluorescent lamp and the operating circuit are designed for operating from a 240 volt or greater alternating current supply. But it is highly desirable for reasons of economy and availability to employ a semiconductor rated at, that is, capable of impeding only about 120 volts, and incapable of operating on the 240 volt supply.

While it would be possible to provide a special transformer or other power consuming circuit to reduce the supply voltage to that for which the semiconductor is rated, it is the object of the present invention to use an existing component of the operating circuit to perform both its usual function and also the function of providing the rated voltage of the semiconductor although only a substantially higher voltage alternating current is available.

According to the invention a circuit for an arc discharge lamp having heated filaments and operating at a predetermined high voltage comprises filament and discharge terminals for connection to a supply of said high voltage alternating current, a power circuit connecting said power terminals to said discharge terminals including electronic valve means for applying periodic voltage pulses to said discharge terminals thereby to support an arc discharge by ionization in the lamp and to draw current from said alternating current supply, said valve means being adapted to impede only an applied voltage substantially lower than said predetermined high voltage, and a transformer including a primary connected between said power terminals, a secondary connected to said filament terminals for supplying heating current thereto, and an output connected to, and for supplying current to, said valve means at substantially lower voltage.

For the purpose of illustration typical embodiments 3,479,558 Patented Nov. 18, 1969 of the invention are shown in the accompanying drawing, in which:

The figure is a schematic diagram of high voltage fluorescent lamp operating circuit according to the invention.

As shown in the figure two eight foot HO fluorescent lamps L (which may be considered as one lamp) have filaments which when heated to emission provide a source of electrons for ionizing the mercury vapor and gas fill of the lamp. The filaments f are connected to discharge terminals 1. The lamps L are designed for operation on a 240 volt supply. Power for the lamps is supplied from 240 volt, 6O cycle alternating current terminals A and C. Power terminal A is connected to a lamp terminal I through an autotransformer primary T1 and secondary T2 having a turns ratio of l to 3 and very low reactance compared to a conventional ballast. Power terminal C is connected directly to a lamp terminal I. A core transformer comprises a primary T3 and secondaries T4 for supplying heating current at about 3.5 volts to the filaments f. The core transformer is of negligible reactance compared to a conventional ballast.

A voltage pulse discharging circuit includes a triac V1 (G.E. type SC45B), a diac D1 (G.E. type 8T2), a primary voltage pulse storage capacitor C1 (6 microfarad) a secondary storage capacitor C2 (0.33 microfarad) and a coupling capacitor C3 (0.07 microfarad). Separable connectors 1, 2 and 3 indicate that the coupling capacitor C3 may be connected by the male connection 1 to either of the two female connectors 2 or 3. Connector 2 leads through a resistor R1 kilohms) to a junction between capacitor C1 and valve V1. Connector 3 leads directly to the power terminal A. The primary storage capacitor C1 and triac T1 are connected in series through the autotransformer primary T1, so that during each half-cycle of alternating current the primary storage capacitor C1 charges through the triac T1. In the succeeding half-cycle the voltage across the secondary capacitor C2 rises toward the breakdown voltage of the diac D1. When this breakdown voltage is exceeded the diac D1 conducts allowing the secondary capacitor C2 to discharge to the gate electrode g of the triac and trigger the triac into avalanche conduction. The primary capacitor then discharges through the triac and autotransformer primary and reverses its charge. The discharge voltage is stepped up by the l to 3 ratio of primary to secondary, and the stepped up voltage (e.g. 600 volts peak) is applied to the lamp terminals I. At this instant a limited number of ions are established in the lamps L, and the lamps fully ignite and conduct line current for part or all of the half-cycle. About when the line voltage passes through zero the arc tends to extinguish, but does not if amplitude and duration of the ionizing pulse has produced suflicient ionization to maintain discharge until the next succeeding ionizing pulse is applied.

While alternating current is supplied to the lamps L at 240 volts, a more economical and available triac and diac, rated for volt operation, are used. According to the invention no components need be added to the abovedescribed circuit. A tap t, mid-way between the ends of the existing filament transformer primary T3, is connected to one primary electrode ec of the triac. The RMS voltage of 120 volts provided by the tap t is correct for the rated voltage of the triac and diac, and is in phase with the alternating current applied to the lamp. Furthermore, the addition of bulky and power-consuming low voltage sources is avoided.

Accordingly it should be understood that this disclosure is for the purpose of illustration only and that the invention includes all modifications and equivalents falling within the scope of the appended claims. For example, other electronic valves, such as two Delco type 2N1412 transistors rated for relatively low voltage operation, may be connected in parallel in opposite polarity to apply ionizing pulses to the lamps.

I claim:

1. A circuit for operating an arc discharge lamp having heated filaments and operating at a predetermined high voltage comprising:

filament and discharge terminals for connection to the lamp,

power terminals for connection to a supply of said high voltage alternating current,

a power circuit connecting said power terminals to said discharge terminals,

a pulse discharging circuit including electronic valve means for applying periodic voltage pulses to said discharge terminals thereby causing the lamp to support an arc discharge by ionization in the lamp and to draw current from said alternating current supply, said valve means being adapted to impede only an applied voltage substantially lower than said predetermined high voltage,

a transformer including a primary connected between said power terminals, a secondary connected to said filament terminals for supplying heating current thereto, and an output connected to, and for supplying current to, said valve means at said substantially lower voltage, and

additional means compling said valve means to said discharge terminals.

2. A circuit according to claim 1 wherein said transformer output comprses a tap connected intermediate the ends of said primary.

3. A circuit according to claim 1 wherein said transformer is connected to step down the voltage at said power terminals.

4. A circuit according to claim 1 wherein said additional coupling means includes a step-up transformer connected between said valve means and said discharge terminals.

References Cited UNITED STATES PATENTS 3,l70,085 2/196'5 Genuit 3l5-273 X 3,235,769 2/1966 Wattenbach 3l5176 3,336,501 8/1967 Segawa 315-289 X JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.R.