US3746920A

US3746920A - Lightweight xenon lamp igniter

Info

Publication number: US3746920A
Application number: US00201666A
Authority: US
Inventors: J Flatley
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1971-11-24
Filing date: 1971-11-24
Publication date: 1973-07-17
Anticipated expiration: 1990-07-17

Abstract

A high voltage diode in combination with a vacuum relay and a low voltage power supply provide an ignition circuit for a Xenon lamp, eliminating the use of a heavy and continuous duty high voltage pulse transformer. This permits appreciable reduction in weight of the ignition circuit, which also produces much less radio frequency interference than a conventional spark discharge type igniter.

Description

ited

tent [191 Flatley 1 July 17, 1973 LIGHTWEIGHT XENON LAMP llGNllTER 3,280,369 10/1966 Baum et a1 315/172 X Inventor: James P. y, Norwich Conn 3,539,863 11/1970 Hogan 315/171 [7 3] Assignee: The Unltedl States 011 America as Prima ry Examiner-Roy Lake gf i p g of the Assistant Examiner-Lawrence J. Dahl as mgton Attorney-Richard S. Sciascia and Louis B. Apple- [22] Filed: Nov. 241, 119711 baum [52] U 8 Ci 315/170 35" 315,172 A high voltage diode in combination with a vacuum Ens/DIG 5 3IS/DIG relay and a low voltage power supply provide an igni- [51] Km m Hash 37/00 tion circuit for 21 Xenon lamp, eliminating the use of a [58] i 5 DIG 7 heavy and continuous duty high voltage pulse trans- 315/176 1 former. This permits appreciable reduction in weight of the ignition circuit, which also produces much less 5 6} References Cited radio frequency interference than a conventional spark UNlTED STATES PATENTS dlscharge type lgmter 3,271,620 9/1966 Webb 3l5/D1G. 5 7 Claims, 1 Drawing Figure Era/Mme 2 i 4 28 w 5w 6 1 55-32?" /C AS47196. 3

1 LIGHTWEIGHT XENON LAMP IGNITER STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or thereafter.

BACKGROUND OF THE INVENTION This invention relates to a novel Xenon lamp igniter.

The successful ignition of a Xenon lamp or the like requires three voltages: a momentary high voltage of the order of to kilovolts, applied between its two electrodes, and used to ionize the enclosed Xenon gas; a momentary medium high voltage, called plasma voltage, of the order of 100 to 300 volts, applied between the electrodes to sustain the discharge after the high voltage is disconnected whereby the ions form a plasma; and a low voltage, known as the sustainer voltage, of the order of 10 to volts, applied between the electrodes used to sustain the flow of plasma after the medium high voltage is disconnected. The sustainer voltage is supplied by a high current power supply which is current regulated.

The most common method of igniting a Xenon lamp or the like has been to use a spark discharge type of igniter, wherein a high voltage of approximately 2.5 kilovolts is discharged into a pulse transformer by a spark gap device. The secondary winding of the pulse transformer is connected in series with the Xenon lamp and the plasma and sustainer power supplies. Consequently, in case of such an igniter circuit, a high current from the current regulated power supply of the sustainer voltage flows continuously through the secondary winding of the pulse transformer. This makes the pulse transformer bulky and heavy. Furthermore, the presence of this secondary winding in the Xenon lamp circuit also causes a loss in high frequency response when the lamp current is modulated. Besides, the spark discharge generates radio-frequency interference that is often difficult to eliminate. Also, a spark discharge type of igniter is not readily adaptable to operation from 28 volt D.C. mains which are common sources of power in certain types of rivercraft.

SUMMARY OF THE INVENTION The objects arid advantages of the present invention are accomplished by utilizing a Xenon igniter which comprises a vacuum relay, a high voltage diode, a high voltage pulse transformer, and a switchover circuit. A high voltage pulse is generated in the pulse transformer by discharging a charged capacitor through the primary winding of the transformer. This high voltage pulse is applied to the electrodesof the Xenon lamp through the secondary winding of the pulse transformer. causing the Xenon gas enclosed in the lamp to ionize. A medium high voltage is then applied to the electrodes of the lamp for a short duration to maintain discharge through the lamp. A low voltage is then applied from a current controlled power supply to sustain the discharge. The high voltage diode and the vacuum relay are used in the circuit to protect the electronic components of the medium high voltage source and low voltage source from the high voltage pulse.

An object of this invention is to have a light and easily transportable igniter circuit for a Xenon lamp or the like.

Another object is to have a Xenon lamp igniter having a low loss in high frequency response when the lamp is current modulated.

Still another object is to have a Xenon lamp igniter having low radio frequency interference which is generated if a spark discharge type of igniter is used for a Xenon lamp.

An additional object of this invention is to have a Xenon lamp igniter wherein a single D.C. low voltage power supply can be used to provide momentary high voltage and momentary medium high voltage for the igniter.

Othe objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing, the single figure of which illustrates an igniter circuit constructed in accordance with the teachings of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of a Xenon lamp igniter circuit is shown in the attached figure, wherein numeral 2 represents a low DC. voltage (20-30 volts) source, which is a conventional power supply, preferably capable of supplying high current of 10 amperes or higher. The output of the power supply 2 is connected to a first terminal of a single throw, single pole switch 4 having its second terminal connected to the input side ofa current regulator 6. The output of the current regulator 6 acts as a current regulated low voltage source or sustainer voltage source for the Xenon lamp igniter. The second terminal of the switch 4 is also connected to a contact point 12 of a normally closed relay 8, to a first terminal of the solenoid 10 of the relay 8, and to a first terminal of the solenoid 20 of a normally open vacuum relay 18. The second terminal of the solenoid 10 is connected to the second terminal of the solenoid 20. Contact 14 of the relay is normally in contact with contact 12 and is also connected to the input of a subcircuit 49, designated as the plasma power supply, which is a conventional unit for converting a low DC. voltage into an alternating voltage and then stepping up the AC. voltage and converting it to a medium high DC. voltage. The output of the subcircuit 49 acts as a medium high voltage source or plasma power supply. Thus, it is preferred to have both sustainer voltage source and plasma voltage source from the same D.C. low voltage power supply. However, it is possible to use two separate voltage sources without deviating from the spirit of this invention.

The output of the current regulator is connected to anode 30 of diode 28, which has its cathode 32 connected to Contact point 22 of the normally open vacuum relay 18. Contacts 12 and 14 of the relay 8 and contacts 24 and 26 of the vacuum relay 18 are normally connecte'd together and contact 16 is normally not connected to anything. Contact 26 is connected to anode 36 of a high voltage diode 34 and is also connected to a first end of a high value resistor 50 having its second end connected to the output of the plasma power supply 49. Cathode 38 of the high voltage diode 34 is connected to a first electrode of Xenon lamp 40 which has its second electrode connected to ground. Cathode 38 is also connected to one end of the capacitor d2 which has its other end connected to one end of the secondary winding 46 of a high voltage transformer 44. The other end of the secondary winding 46 is connected to ground. The first end of resistor 50 is also connected to one end of a capacitor 52 and one end of resistor 66. The other end of capacitor 52 is connected to one end of resistor 54 and to the cathode 56 of an SCR (silicon controlled rectifier) 58 having its gate electrode 60 connected through a resistor 62 to ground. The anode of the SCR 58 is connected to second terminals of solenoids l and 20. The other end of resistor 54 is corinected to ground. The other end of resistor 66 is connected to the emitter 70 of the unijunction transistor 72 and also connected to one end of resistor 68, which has its other end connected to ground. Ohmic contact 74 of the unijunction transistor 72 is connected to one end of the resistor 76, which has its other end connected to contact 14 of the relay 8. Ohmic contact 78 of the unijunction transistor 72 is connected to gate electrode 82 of SCR (silicon controlled rectifier) 84 as well as to one end of resistor 80, having its other end connected to ground. SCR 84 has its cathode connected to ground, and its anode 88 connected to the first end of resistor 50 as well as to one end of capacitor 90. The other end of capacitor 90 is connected to one end of the primary winding 48 of the transformer 46, the other end of the primary winding being connected to ground.

OPERATION OF THE CIRCUIT When switch 4 is closed, an adjustable low voltage (20-30 volts), high current l amperes) conventional power supply provides input to the current regulator 6. The output of the current regulator is then available as a source of low voltage, regulated high current acting as a sustainer power supply for the igniter. Output of the power supply 2 also supplies input to the plasma power supply 49 through the contacts 12 and 14 of the normally closed relay 8 and is connected to the ohmic contact 74 of the unijunction transistor 72. The resistance of the n-type silicon of the unijunction transistor acts like a voltage divider to establish a potential at the emitter contact 70, which makes the emitter junction reverse biased. The output of the plasma supply is medium high DC. voltage, preferably 250 volts, charges capacitor 52 with a time constant of a few tenths of a second, equalling product of the values of resistor 50 and capacitor 52, which makes the ungrounded end of the current sensing resistor 54 negative with respect to ground. During the charging of capacitor 52, when capacitor 52 is almost fully charged, the voltage

divider comprising resistors

66 and 68 provides enough positive potential to emitter contact 70 of the unijunction transistor to make the emitter junction of the unijunction transistor forward biased and conduct, thus providing sufficient gate electrode current in SCR 84 to make it conduct and provide a high voltage pulse to the primary winding 48 of the high voltage transformer 44 through capacitor 90. This high voltage pulse is transferred to the secondary winding 46 of the high voltage transformer 44 and is then applied to the Xenon lamp 40 through an isolating capacitor 42, and thus ionizing the gas enclosed in the Xenon lamp. High voltage diode 34 protects the plasma power supply and the current regulator from this high voltage pulse. The size of the high voltage pulse is preferably -15 kilovolts of about I millisecond duration whereas the plasma power supply delivers preferably 250 volts for 3 to 5 milliseconds. After 3 to 5 milliseconds from the time an input is supplied to the plasma power supply circuit, due to charging of capacitor 52, the ungrounded end of resistor 54, which is connected to the cathode 56 of SCR 58, becomes sufficiently negative to provide enough gate electrode current thereof and thus SCR 58 starts conducting. Due to conduction by SCR 58, relay 8 and vacuum relay 18 are energized. Relay 8 when energized connects contacts 14 and 16 thereof and deprives plasma power supply circuit of its input from the power supply 2. Vacuum relay 18, when energized, connects its

contacts

22 and 26, thus applying the output of the current regulator 6 which acts as a sustainer power supply for the Xenon lamp 40. The diode 28 is used to protect the current regulator 6 from the output of the plasma power supply circuit.

Briefly stated, when switch 4 is closed, output of power supply 2 is supplied to the current regulator 6 and the plasma power supply as their inputs. Plasma power supply provides as its output a medium high voltage, 250 volts, for 3 to 5 milliseconds after which its input is turned off. The output of the plasma power supply generates a high voltage signal of 10-15 kilovolts for a millisecond in the secondary winding 46 of high voltage pulse transformer 44, which is applied to the Xenon lamp to ionize the gas enclosed. The me dium high voltage is then used to maintain the plasma inside the Xenon lamp for the remaining period. After 3 to 5 milliseconds, the input to the plasma power supply is turned off and the output of the current regulator 6 is applied to the Xenon lamp to sustain the discharge. This circuit thus eliminates the use of a heavy and bulky high voltage transformer and makes the igniter circuit light and easily transportable.

Obviously many modifications and variations of the present invention are possible in the light of above teachings. As an example, it may be possible to use separate low voltage and medium voltage power supplies instead of using a single low DC. voltage power supply as discussed above. It is therefore understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. An igniter circuit for a gas filled electric lamp having a first electrode and a grounded second electrode comprising:

a first power supply adapted to provide a DC. voltage;

a current regulator having its input connected to the output ofsaid first power supply and its output coupled to the first electrode of said lamp;

a second power supply for stepping up the output voltage of said first power supply, the input of said second power supply being coupled to the output of said first power supply and the output of said second power supply being coupled to said first electrode of said lamp;

a timing circuit including a unijunction transistor having a first ohmic contact coupled to the output of said first power supply, an emitter contact coupled to the output of said second power supply, and a second ohmic contact;

means for maintaining the second ohmic contact of said unijunction transistor above ground potential;

a first normally closed switching element coupling the output of said first power supply to the input of said second power supply and to said first ohmic contact;

a second normally open switching element coupling the output of said current regulator to the output of said second power supply and to said first electrode;

means for isolating the output of said current regulator from the output of said second power supply;

a voltage pulse transformer having its primary winding coupled to said second ohmic contact and its secondary winding coupled to said first electrode; and means driven by said timing circuit for actuating said first and second switching elements a predetermined time after energization of said second power supply, thereby applying the output of said current regulator and disconnecting the output of said second power supply from said first electrode.

2. The igniter circuit of claim 1 wherein the means for isolating the output of said current regulator from the output of said second power supply is a first diode having its anode connected to the output of said current regulator and its cathode coupled to the output of said second power supply.

3. The igniter circuit of claim 2 wherein a second diode is interposed between the secondary winding of said pulse transformer and output of said second power supply to protect said second power supply from a voltage pulse from the secondary winding of said pulse transformer.

41. The igniter circuit of claim 3 wherein said first switching element comprises a first solenoid relay having its first terminal connected to the output of said first power supply and its second terminal connected to said timing circuit.

5. The igniter circuit of claim 4 wherein said second switching element comprises a second solenoid vacuum relay, the solenoid of said second relay having its first terminal connected to the output of said first power supply and its second terminal connected to the second terminal of the solenoid of said first relay.

6. The igniter circuit of claim 5 wherein the timing circuit further comprises:

a first SCR having its anode coupled to the output of said second power supply and also coupled to the primary winding of said pulse transformer, said SCR being biased to conduct upon conduction of said unijunction transistor, thereby providing a signal to the primary winding of said pulse transformer.

7. The igniter circuit of claim 1 wherein the means for maintaining the ohmic contact of said unijunction transistor above ground potential is a resistor.

Claims

1. An igniter circuit for a gas filled electric lamp having a first electrode and a grounded second electrode comprising: a first power supply adapted to provide a D.C. voltage; a current regulator having its input connected to the output of said first power supply and its output coupled to the first electrode of said lamp; a second power supply for stepping up the output voltage of said first power supply, the input of said second power supply being coupled to the output of said first power supply and the output of said second power supply being coupled to said first electrode of said lamp; a timing circuit including a unijunction transistor having a first ohmic contact coupled to the output of said first power supply, an emitter contact coupled to the output of said second power supply, and a second ohmic contact; means for maintaining the second ohmic contact of said unijunction transistor above ground potential; a first normally closed switching element coupling the output of said first power supply to the input of said second power supply and to said first ohmic contact; a second normally open switching element coupling the output of said current regulator to the output of said second power supply and to said first electrode; means for isolating the output of said current regulator from the output of said second power supply; a voltage pulse transformer having its primary winding coupled to said second ohmic contact and its secondary winding coupled to said first electrode; and means driven by said timing circuit for actuating said first and second switching elements a predetermined time after energization of said second power supply, thereby applying the output of said current regulator and disconnecting the output of said second power supply from said first electrode.

4. The igniter circuit of claim 3 wherein said first switching element comprises a firsT solenoid relay having its first terminal connected to the output of said first power supply and its second terminal connected to said timing circuit.

6. The igniter circuit of claim 5 wherein the timing circuit further comprises: a first SCR having its anode coupled to the output of said second power supply and also coupled to the primary winding of said pulse transformer, said SCR being biased to conduct upon conduction of said unijunction transistor, thereby providing a signal to the primary winding of said pulse transformer.