US2727188A - Starting circuit for lamps - Google Patents

Description

Dec. 13, 1955 c. M. RIVELY 2,727,188

STARTING CIRCUIT FOR LAMPS Filed March 26, 1953 INVENTOR CLAIR M. RIVELY A ORNEY United States Patent @ffice 2,727,188 Patented Dec. 13, 1955 STARTING CIRCUIT FOR LAMPS Clair Michael Rively, Rockaway, N. J assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application March 26, 1953, Serial No. 344,764 Claims. (Cl. 315180) This invention relates to a starting circuit for a lamp which contains an ionizable atmosphere for conducting the current and more particularly to a circuit for starting such a lamp having cold cathodes.

A lamp which contains an ionizable atmosphere (one comprising a gas, a vapor, or a combination of gas and vapor) requires a voltage to ignite it which is higher than the voltage necessary to maintain conduction once the lamp has lit. A method of improving the starting characteristics of such lamps was to heat the cathodes to a temperature suflicient to emit electrons. The line voltage applied to the lamp accelerated the electrons and collisions between the moving electrons and the molecules of the atmosphere produced ionization. Automatic switches were used to control the heating of the cathodes. Such methods produced erratic results and long delays in lighting, and the automatic switches were subject to repeated breakdowns.

High intensity leinps, such as mercury lamps used for projection purposes, may contain gas or vapor under a pressure as great as ten atmospheres. To ignite such lamps without first heating the cathodes would require between 40,000 and 50,000 volts. After ignition, the voltage required is less than the 110 volts used as the supply for the lamp. Full lamp current is often as high as 300 amperes. Means must be provided, in a circuit which is to successfully ignite these lamps instantl for supplying an extremely high voltage for starting and a much lower voltage but high current for normal operation.

it is an object of this invention to provide a dependable circuit for readily starting a lamp having an ionizable atmosphere and cold cathodes.

A further object of this invention is to provide a circuit for readily starting and operatin a lamp having an ioniza'nle atmosphere, which circuit utilizes a single transformer to supply starting energy to the lamp and to ballast the lamp during operation.

Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawings, which illustrate a preferred embodiment, and wherein the single fi ure is a schematic illustration of the starting circuit of this invention.

A lamp 11 is connected to a source of alternating current 12 by terminals 13 and conductors 14 and 15. Connected between the conductors 14 and 15 is a capacitor 16 which is connected in series with a primary Winding 17 of an iron-core step-up transformer 13. The secondary winding 19 of the transformer 18 is connected in series with an electric discharge device 21 (shown as a spark gap) in an oscillatory loop 20. A pulse transformer 22 transfers energy from the oscillatory loop to the lamp 11. The primary winding 23 of the transformer 22 is connected in series with the secondary winding 19 and the electric discharge device 21. A capacitor 26 is connected across the secondary Winding 19 and tunes the inductance of the primary 23. The

secondary winding 2 of the transformer 22 acts as a ballast for the lamp 11 besides providing a large voltage pulse for igniting the lamp 11, and the iron core 25 of the transformer 22 is provided with an air gap to reduce losses When the secondary winding 24 carries full lamp current. Across the secondary winding 24, a protective discharge device 27 is connected to prevent excessive voltage from damaging the secondary winding 24. To prevent any oscillations generated in the oscillatory loop 20 from entering the alternating current source 12 and the primary winding 17, filters are provided in the form of a capacitor 253 connected across the supply lines 14 .nd adjacent the terminals 13, a radio frequency 0. e 29 connected in series with the primary 17, and capacitor by-passing the primary 17. A connection 1 is made between the oscillatory loop 29 and the extercircuit to prevent the loop 20 from floating.

If the lamp 11 is not lit, substantially full line voltage is a plied across the primary winding 17 and the capacitor 16. At this voltage and at the frequency of the c-.rce 12, the primary winding 17 and the capacitor 6 resonate. A large voltage appears across the primary winding 17 and is transformed and multiplied by the transformer so that a voltage many times that of the source 12 appears across the secondary winding 19.

The capacitor 26 is charged by the secondary winding 1h until the voltage across the capacitor 26 is sufiicient to breakdown the spark gap 21. Hi h frequency oscillations are then generated in the loop 20. Due to the rapid variation of the current in the primary Winding 23 of the transformer 22, high voltages are induced in the secondary winding 24 and are applied to the lamp 11 to ignite it. After the lamp 11 has ignited, the secondary winding 24 acts as a ballast, limiting the current flow. The voltage drop produced across the secondary Wind- 'oy the lamp current flowing through it, reduces the voltage applied to the primary winding 17 of the transformer 18 and the inductance of the primary winding 17 is c so that it no longer resonates with the capacitor 1-6. This occurs because of the change of the saturation in the iron core of the transformer 18 with a change in the current flowing through the windings. As the saturation of the core changes, the inductances of th windings also change.

The breakdown of the spark gap 21 is sudden, and the initiation of current flow through the primary Winding 23 of the transformer 22 is also sudden. The voltage induced in the secondary winding 24 is a transient pulse and the transformer 22 must be designed to pass transient pulses readil if the circuit is to operate properly. It has been found that when the secondary winding 24 carries the full current of the lamp 11, there is a tendency for the secondary winding 24- to overheat. Overheating is caused by saturation of the core 25 and its attendant hysteresis loss. To reduce saturation, the core 25 is provided with an air ap thereby reducing the hysteresis loss and the overheating to a safe value With very little increase in physical size and substantially no loss in performance.

To prevent sustained oscillation of the oscillatory loop 20 due to feed back of the high frequency energy, a radio frequency choke 29 is provided to keep high frequency energy from entering the primary winding 17 from the line 1 A by-pass capacitor 30 is also provided to shunt high frequency energy around the primary winding 17, and capacitor 23 acts as a high frequency by-pass around the source 12.

It will be apparent from the above that this invention provides a simple, yet reliable, starting circuit for lamps which contain ionizable atmospheres. In addition, a transformer has been provided, the secondary of which also functions as a ballast, thus reducing the number of elements required. Since no moving parts are required forthe circuit of this invention, maintenance costs are kept low.

Obviously, many modifications and variations of this invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A starting circuit for a lamp which contains an ionizable atmosphere, said circuit comprising an oscillatory loop containing an electric discharge device; first means for transferring energy from said oscillatory loop to said lamp, said first means comprising a first transformer which comprises a first primary winding, a first secondary winding, and a first iron core, said first primary winding being connected in said oscillatory loop in series with said electric discharge device, said first secondary winding being connected in series with said lamp so as to be traversed by current passing through said lamp, said iron core having an air gap to reduce saturation; a capacitor; and second means for energizing said oscillatory loop, said second means comprising a second transformer which comprises a second primary winding, a second secondary winding and a second iron core, said second secondary winding being connected in said oscillatory loop in series with said first primary winding and said electric discharge device, said second primary winding and said capacitor being connected across said lamp as a series circuit which is tuned at a predetermined vol"- age and frequency, said second iron core being r sponsive to full lamp current through said first secondary winding to detune said second primary winding and said capacitor.

2. A starting circuit for a high intensity lamp which contains an ionizable atmosphere, said circuit comprising a first conductor and a second conductor each adapted to have a-first end connected to a source of alternating current and a second end connected to said lamp, a first transformer comprising a first primary winding and a first secondary winding, a first capacitor of a value proper to resonate with said first primary winding at a predetermined voltage and frequency, conductors to connect said first primary winding and said first capacitor in series between a point on said first conductor and said second conductor, an electric discharge device, an oscillatory loop comprising said electric discharge device and said first secondary winding connected in series, and a second transformer comprising a second primary winding, a second secondary winding, and an iron core, said second primary winding being connected in said oscillatory loop in series with said electric discharge device and said first secondary winding, said second secondary winding being interposed in series in said first conductor between said first end and said point, said iron core having an air gap to limit saturation, the flow of full lamp current through said second secondary winding producing a voltage drop which changes the voltage applied to said first primary winding and said first capacitor causing them to cease resonating.

3. A starting circuit for a lamp which contains an ionizable atmosphere, said circuit comprising an oscillatory loop comprising a spark gap; first means for coupling said loop to said lamp, said first means comprising a first transformer which comprises a first primary Winding, a first secondary winding and a first iron core, said first secondary winding being connected in series with said lamp, said first primary winding being connected in said oscillatory loop in series with said spark gap, said iron core having an air gap to limit saturation; a second spark gap connected across said first secondary winding; a choke coil; a first capacitor; second means for energizing s aid oscillatory loop, said second means comprising a second transformer which comprises a second primary winding, a second secondary winding, and a second iron core, said second secondary winding being connected in said oscillatory loop in series with said first primary winding and said first spark gap, said second primary winding, said choke coil and said first capacitor being connected in a series circuit which resonates at a predetermined frequency and voltage, said series circuit being connected across said lamp and being responsive to full lamp current fiowingthrough said first secondary winding to drop out of resonance; a second capacitor connected across said second secondary winding; and a third capacitor connected across said second primary to by-pass high frequency oscillations around said second primary winding.

4. A starting circuit for a lamp which contains an ionizable atmosphere, said circuit comprising terminals for connection to a source of alternating current, a first conductor and a second conductor each having a first end connected to said terminals and a second end adapted to be connected to said lamp, a first transformer having a first primary winding and a first secondary winding, a first capacitor, conductors to connect said first primary windin and said first capacitor in series between a point on said first conductor and said second conductor, said first capacitor and first primary winding forming a circuit which is tuned ata predetermined voltage and fre quency, an oscillatory loop comprising said first second ary winding and an electric discharge device connected in series, a second capacitor connected across said first secondary winding, a second transformer having a second primary winding and a second secondary winding, said second primary winding being connected in said oscillatory loop in series with said first secondary winding and said electric discharge device, said second secondary winding being interposed in said first conductor between said first end and said point, said first transformer being responsive to the flow of full lamp current through said second secondary winding to detune said tuned circuit, a third capacitor connected between said terminals to bypass any oscillations produced by said oscillatory circuit, and a connection between said oscillatory loop and said second conductor to prevent said oscillatory loop from floatin 5. A starting device and operating circuit for a cold cathode lamp which contains an ionizable atmosphere, said starting device comprising a pulse transformer having a primary winding, a secondary winding, and an iron core, each said lamp and said secondary winding being provided with terminals 'for connection to external cir-- cuits, a first lead adapted to connect one of said lamp terminals to a source of alternating current, a second lead connected at one end to one of said secondary winding terminals, the other end of said second lead being adapted for connection to the other of said lamp terminals, a third lead connected at one end to the other of said secondary winding terminals, the other end of said third lead being adapted for connection to said source of alternating current, a capacitor, a spark gap, leads connecting said capacitor, said spark gap and said primary winding in series, and means connected between said first and second leads for impressing across said capacitor a high alternating potential of a magnitude sutficient to fire said spark gap, the transformer ratio of said pulse transformer being sufiiciently high to induce a voltage in said secondary winding to ignite said lamp when said sparlc gap fires, the impedance of said secondary winding forming the ballast for said lamp, and said iron core having an air gap to reduce the magnetization of said iron core by the operating current of said lamp.

6. A starting and operating circuit for a lamp in which the illuminating media comprises an ionizable atmos phere, said circuit comprising a ferromagnetic pulse transformer having a primary winding and a secondary winding, said secondary winding adapted to be connected in series with the lamp and an alternating current power supply and having an impedance suliicient to provide the ballast for stable operation of the lamp, and means coupled to said primary winding and adapted to be coupled to the alternating current power supply for applying a high frequency voltage to said primary winding to induce a voltage in said secondary winding sufiicient to ionize the atmosphere in the lamp.

7. A starting circuit for a lamp which contains an ionizable atmosphere, said circuit comprising; a ferromagnetic pulse transformer having a primary winding and a secondary winding, said secondary winding adapted to be connected in a series circuit including an alternating current power supply and a lamp and to serve as a ballast for the lamp when the lamp is lighted; an oscillatory loop including said primary winding for converting energy obtained from the power supply and at the frequency of. the power supply into high-voltage high-frequency energy for efiicient transfer through said pulse transformer to light the lamp; means adapted for connection across the lamp and active only when the lamp is not conducting for transferring sufiicient power-frequency energy to said oscillatory loop to cause the latter to oscillate; and filter means for keeping high-frequency energy generated in said oscillatory loop out of said last-mentioned means.

8. A starting circuit for a lamp which contains an ionizable atmosphere, said circuit comprising; a circuit branch adapted for connection in shunt across the lamp; means associated with said circuit branch for causing the circuit branch to be tuned to power supply frequency when a predetermined power supply voltage is applied across said circuit branch and to be detuned when a reduced power supply voltage is applied across said circuit branch; an oscillatory circuit associated with said means and adapted to obtain suflicient energy from said circuit branch for oscillating only when said circuit branch is tuned; a ballast for connection in series with the lamp and a power supply; and means in said oscillatory circuit associated with said ballast for transferring high-voltage high-frequency energy from said oscillatory circuit to said ballast to cause the lamp to light, said circuit branch being automatically detuned when said ballast carries full lamp current.

9. A starting circuit for a lamp which contains an ionizable atmosphere as recited in claim 8 and further comprising means connected across said ballast for limiting the voltage amplitude applied across said ballast.

10. A starting and operating circuit for a lamp in which the illuminating media comprises an ionizable atmosphere, said circuit comprising a ferromagnetic pulse transformer having a primary winding, a secondary Winding and a core formed with an air gap, said secondary winding adapted to be connected in series with the lamp and an alternating current power supply for the lamp and having an impedance sufilcient to provide the ballast for stable operation of the lamp, and means coupled to said primary winding and adapted to be coupled to the alternating current power supply for applying a voltage pulse with a steep leading edge to said primary winding to induce a high voltage with a steep leading edge in said secondary winding to ionize the atmosphere in the lamp.

Pirani et al. July 5, 1938 Von Henke July 14, 1942

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