US3745411A

US3745411A - Current supply device for a gas-and/or vapour discharge lamp

Info

Publication number: US3745411A
Application number: US00086471A
Authority: US
Inventors: J Polman; Der Were J Van
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1969-11-10
Filing date: 1970-11-03
Publication date: 1973-07-10
Anticipated expiration: 1990-07-10
Also published as: GB1276409A; SE356424B; CH522347A; NL6916934A; FR2069107A5; DE2053517A1; NL166598C; NL166598B; BE758717A; AT298615B; DE2053517C3; DE2053517B2

Abstract

The invention relates to a device for supplying an intermittent current to a gas- and/or vapour discharge lamp. According to the invention an intermittent current is used in which the effective period is considerably shorter than the subsequent rest interval, whilst the pressure in the discharge space of the lamp is chosen to be comparatively high. This combination of a short effective period and a high pressure together with an appropriate choice of the frequency provides on the one hand a high light output of the lamp and on the other hand a long lifetime thereof. The potential increases in luminous efficiency provided by the invention is considerable.

Description

United States Patent 1191 1111 3,745,41 1 Polman et ai. 1 1 July 10, 1973 [5 CURRENT SUPPLY DEVICE FOR A 3,075,123 l/1963 Faulds 315 209 R GASANDIOR VAPOUR DISCHARGE LAMP 1,996,520 4/1935 Marshall, Jr... 315/209 R 1 3,061,744 /1962 Spira 315/209 R X Inventors: J Polman; J rt a e 3,310,708 3/1967 Seidler 315/209 R x Were, both of Emmasingel, 3,265,930 8/1966 Powell, Jr. 315/209 R Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New York, Primary miner-Nathan Kaufman Att0rneyFrank R. Trlfarl [22] Filed: Nov. 3, 1970 [57] ABSTRACT [21] Appl. No.: 86,471

The 1nvent1on relates to a dev1ce for supplying an intermittent current to a gasand/or vapour discharge lamp. [301 Forelgn Apphcatmn Pnomy Data According to the invention an intermittent current is Nov. 10, 1969 Netherlands 6916934 used in which the effeciive period is considerably shorter than the subsequent rest interval, whilst the [52], [1.8. CI 315/209 R, 315/272, 315/201 pressure in the discharge Space of the lamp is chosen [51] Int. Cl. H05b 37/02 to be comparatively high This combination Of a short [58] Field of Search 315/172, 209 R, 272, effective period and a high pressure together i an 315/246, 224, 98; 313/109 appropriate choice of the frequency provides on the one hand a high light output of the lamp and on the [56] References Clted other hand a long lifetime thereof.

UNITED STATES PATENTS The potential increases in luminous efficiency provided 2,538,062 l/ll TOUVCI 3l5/20l X by the invention is considerable, 2,525,900 8/1970 Skirvin et a1 315/98 3,536,945 10/1970 Skirvin 313/109 X 6 Claims, 3 Drawing; Figures PATENIEUJUHOW I 3.745.411

Fig.3

JAN POLMAN JAN E. VAN DER WERF 2 1: AGE

CURRENT SUPPLY DEVICE FOR A GAS-AND /OR VAPOUR DISCHARGE LAMP This invention relates to a device comprising a lowpressure gas and/or vapour discharge lamp, in which two input terminals of the device are connected to each other by a series combination of at least the lamp and a switching element, the latter being connected to a control-device which controls said switching element so that the lamp is traversed by an intermittent current, in which a time interval of W seconds during which the lamp is traversed by current is followed by an at least equally long, substantially idle, time interval of R seeonds.

The term low pressure is to denote herein a pressure of at the most 150 Torr.

A known device of the kind set forth is disclosed in French Pat. specification Nr. 1,456,460. This known device has the advantage of a comparatively high luminous efficiency (for example, expressed in Lumen/- Watt). In the embodiment described in said French Pat. specification the time W is equal to the time R. If, in order to increase the light output, the ratio W/(W+R) were chosen to be lower than one-half, while the lamp power is kept constant, the current peaks might have such a high intensity that material would soon sputter from the electrodes of the lamp. This could be detrimental to the lifetime of the lamp.

An object of the invention is to provide a device in which the luminous efficiency of the discharge lamp is very high and also the lifetime of the lamp is long.

A device according to the invention, comprising a low-pressure gas and/or vapour discharge lamp in which two input terminals of the device are connected to each other by a series combination of at least the lamp and a switching element, the latter being connected to a controLdevice which controls said switching element so that the lamp is traversed by an intermittent current, in which a time interval of Wseconds during which current passes through the lamp is followed by an at least equally long, substantially idle, time interval of R seconds, is characterized in that in order to obtain a condition favourable for the production of light the pressure in the discharge space is at least 4 Torr and is in addition so high that the condition 7,; 1,, is fulfilled and in that the ratio W/( W+R) is lower than 0.4 and in that the duration of a period W+R of the supply to the lamp has a value lying between 21r TE and 271 1 wherein:

T3 is the energy relaxation time (in seconds) of the electrons in the discharge space and 7,, is the diffusion time (in seconds) of the electrons in the discharge space.

The term energy relaxation time is to be understood to mean herein: l/A.B, wherein:

A is the average fractional energy loss per collision of an electron (fractional is to denote herein that the energy loss is expressed in the energy of the electron prior to the collision), and

B is the average number of collisions of an electron with non-electron particles in the discharge space per second.

The term diffusion time is to denote herein the time (expressed in seconds) required on an average by an electron to reach the wall of the discharge space.

The device embodying the invention has the advantage that the luminous efficiency may be very high owing to the comparatively low value of the ratio between the current time interval (W) and the substantially idle time (R) on the one hand and a given range of the period (W R) on the other hand, and because a lamp having a comparatively high pressure in the discharge space is used. It is a further advantage that the comparatively high pressure in the discharge space counteracts sputtering from the lamp electrodes. in a device embodying the invention the lamp may therefore have a long lifetime.

The invention is furthermore based on the recognition that with the chosen period W+ R the electron gas cools down during the idle time interval by collisions until it has reached the temperature of the neutral gas, while during this time interval the electron concentration has diminished only slightly. The extent of concentration drop is determined by the diffusion time T which is longer than the time interval (W+R)/2w.

The current pulse following an idle time interval reheats the electron gas and it is found that then a comparatively large number of high-velocity electrons is obtained, that is to say a number larger than is obtained in a corresponding situation with direct-current operation of the lamp by the same average current. The efficiency of a gas discharge is favourably affected by the presence of a comparatively large number of highvelocity electrons.

The discharge space may contain a rare gas, for example, argon, and/or a metal, for example, mercury.

In an advantageous device embodying the invention, in which the gas in the discharge space is neon, the pressure of the neon is of the order of 5 to 25 Torr, while the ratio W/( W+R) is at the most 0.3 and the duration W+R of a period of supply to the lamp lies between 4.10 and 50.10" sec.

This preferred device has the advantage that with a suitably chosen pressure the obtainable light output may even be as much as six times that obtained with a direct current supply (the lamp power being the same).

The invention will be described more fully with reference to the accompanying drawing, wherein FIG. 1 shows a circuit arrangement of a device embodying the invention;

FIG. 2 shows a further embodiment of a circuit arrangement of the device; and

FIG. 3 shows a further embodiment of the circuitry of the device.

Referring to FIG. 1, reference numerals I and 2 designate connecting terminals for a direct-current source of, for example, 200 V. The terminals 1 and 2 are connected by a series combination of a discharge lamp 3, a series resistor 4 and the main electrodes of a transistor 5. The base of the transistor is connected to a pulse generator 6. A junction between the lamp 3 and the emitter of the transistor 5 also is connected to the pulse generator 6. The pulse generator 6 is fed via connecting terminals 7 and 8, connected to an altemating-current supply of 220 V, 50 Hz.

The pulse generator 6 is adjusted so that pulses of a duration of about 25 p.866 are produced, each pulse being followed by an idle period of about usec.

The lamp 3 was a neon lamp having an operating voltage of about V (with direct-voltage supply). The length of this lamp was about 750 mms and the diameter was 36 mms. The pressure of the neon gas was about 10 Torr. The electrode material was tungsten with a barium oxide coating.

In this practical case the frequency l/(W+R) was about 8,000 Hz. 1' was about 1,000 psec and T was about 2.5 usec. The sum W+R was about 125 sec. Thus the condition that W+R should lie between 21r TD and Zn 1 is fulfilled. Furthermore W/( W+R) is 0.2.

In order to compare this supply with other supplies of the lamp, the following table indicates data for midnary direct current supply and for the case of W/( W+R) 0.5 and finally for the case in which W/( W+R) 0.2. The latter figure is in accordance with the invention. The table shows the case in which the neon pressure was Torr and the case in which the neon pressure was 5 Torr in a comparable lamp. The numbers in this table indicate the relative lumen values of the lamps under the various conditions expressed in percentages of the lumen value of the 5-Torr lamp driven by direct current. (The lumen value of the latter lamp was about 540 lumens with direct-current supply with a lamp power absorption of 45 W). The frequency was 8 kHz in the cases of the extreme right-hand column and of the second extreme right-hand column. In all cases indicated in the table the lamp power was 45 W.

From these results it will be apparent that the lamp embodying the invention (see the last column) has a higher luminous efficiency (expressed, for example, in lumen/Watt). It appears furthermore that with a higher pressure the increase in efficienvy is even higher than with a low pressure. This higher pressure also brings about a reduced sputtering of electrode material of the lamp.

The lifetime of the indicated lamps embodying the invention was not shorter than that of known discharge lamps with direct-current supply.

If it is desired to supply current to the lamp from a low-frequency A.C. supply, the transistor 5 may be included in a rectifying bridge (diodes 10 to 13) as is shown in FIG. 2. In FIG. 2 reference numeral 3 designates the lamp and 6 denotes the pulse generator.

With current supplied from a low-frequency A.C. supply, two transistors may be used which are included in parallel branches and have opposite pass directions. This is illustrated in FIG. 3. The transistors are designated by reference numerals l5 and 16. A diode l7 and a diode 18 are connected in series with the

transistors

15 and 16, respectively. The bases of the

transistors

15 and 16 are connected to a pulse generator 6". The emitters of the two transistors are also connected to the pulse generator 6". The lamp to be operated is designated by 3". The diodes l7 and 18 serve to protect the transistors.

In the cases shown in FIGS. 2 and 3, a number of current pulses in one direction through the lamp, each followed by rest intervals, is followed by a number of current pulses in the other direction through the lamp, each also followed by rest intervals. This is due to the fact that in these cases the current is supplied to the lamp from a low-frequency A.C. source, i.e., one having a frequency lower than 100 Hz, whereas the pulse generators control the transistors with a considerably higher frequency, i.e., about 8,000 I-Iz.

In the examples described one pulse generator controls one lamp circuit. However, one pulse generator may be employed for controlling more than one lamp circuit (as indicated by the series connection I, 4, 5, 3, 2 in FIG. I), so that to control the supply control of a group of lamps only one pulse generator is required.

What is claimed is:

1. An electric discharge lamp supply system comprising, a pair of input terminals adapted for connection to a source of electric power, an electric discharge lamp having a gas or vapor filling at a pressure of at least 4 Torr and high enough to satisfy the condition that TE TD wherein:

TE is the energy relaxation time (in seconds) of the electrons in the lamp discharge space and 7,, is the diffusion time (in seconds) of the electrons in the lamp discharge space,

a controlled switching element connected in series with the lamp across said input terminals, a control device connected to a control input of the switching element for switching said element to cause an intermittent flow of current to said lamp during a time interval W followed by a time interval R which is at least as long as the time interval W and during which no current flows to the lamp, said control device operating the switching element so that the duty cycle W/( W+R) is lower than 0.4 and the duration of the lamp period W R is limited to the range of values lying between 21m; and 21m 2. A system as claimed in claim 1, the gas in the lamp discharge space is neon, characterized in that the neon pressure is of the order of 5 to 25 Torr and in that W/( W+R) is at the most 0.3 and the duration W+R of a period of the supply to the lamp lies between 4.10 and 50.10 seconds.

3. A system as claimed in claim 1 adapted for connection to an alternating voltage power source of a frequency lower than Hz and characterized in that the switching element comprises a transistor included in a diagonal branch of a rectifying bridge having input terminals connected in series with the lamp and the device input terminals.

4. A system as claimed in claim 1 adapted for connection to an alternating voltage power source of a frequency lower than 100 Hz ancharacterized in that the switching element comprises the combination of two transistors connected in parallel with the transistors having opposite pass directions.

5. A system as claimed in claim 1 wherein said control device comprises a pulse generator supplying trigger pulses to said switching element at a frequency of approximately 8,000 Hz.

6. A high efficiency low pressure electric discharge lamp comprising a sealed glass envelope with a pair of spaced apart electrodes, a pair of external terminals connected to said electrodes and adapted for connection to a source of intermittent lamp supply current that supplies current for a time period of W seconds followed by an off period of R seconds at least as long as the time interval W, the pressure in the discharge space being at least 4 Torr and high enough to satisfy the condition 1 r,, the lamp supply frequency being restricted to a range of frequencies such that W/( W+R) 0.4 and the time period W+R lies between 21r'r and 21",, wherein:

1 is the energy relaxation time (in seconds) of the electrons in the lamp discharge space and TD is the diffusion time (in seconds) of the electrons in the lamp discharge space.

i it ii 1 mg UNITED S'IAlES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,745,411 Dated July 10, 1973 Invent-or(s) JAN POLMAN ET AL It is certified that error appears in the above-identified patent. and that said Letters Patent are hereby corrected as shown below:

col. 1, line 22, before "time" (lst occurrence) insert "on" before "time" (2nd occurrence) insert "off" line 47, before'"sup ly" insert electric lines 51 & 53, after "the" insert lamp col. '2, line 34, before "supply" insert electric line 58, after "Hz" insert (not shown) col." 3, line 18, after "with" (1st occurrence) insert a I after "supply" insert and t i In the claims, col. 4, line 39, cancel "device" and insert system Signed and sealed this 16th day of July 1974. k

1 (SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents

Claims

1. An electric discharge lamp supply system comprising, a pair of input terminals adapted for connection to a source of electric power, an electric discharge lamp having a gas or vapor filling at a pressure of at least 4 Torr and high enough to satisfy the condition that Tau E< Tau D wherein: Tau E is the energy relaxation time (in seconds) of the electrons in the lamp discharge space and Tau D is the diffusion time (in seconds) of the electrons in the lamp discharge space, a controlled switching element connected in series with the lamp across said input terminals, a control device connected to a control input of the switching element for switching said element to cause an intermittent flow of current to said lamp during a time interval W followed by a time interval R which is at least as long as the time interval W and during which no current flows to the lamp, said control device operating the switching element so that the duty cycle W/(W+R) is lower than 0.4 and the duration of the lamp period W + R is limited to the range of values lying between 2 pi Tau E and 2 pi Tau D.

2. A system as claimed in claim 1, the gas in the lamp discharge space is neon, characterized in that the neon pressure is of the order of 5 to 25 Torr and in that W/(W+R) is at the most 0.3 and the duration W+R of a period of the supply to the lamp lies between 4.10 5 and 50.10 5 seconds.

3. A system as claimed in claim 1 adapted for connection to an alternating voltage power source of a frequency lower than 100 Hz and characterized in that the switching element comprises a transistor included in a diagonal branch of a rectifying bridge having input terminals connected in series with the lamp and the device input terminals.

6. A high efficiency low pressure electric discharge lamp comprising a sealed glass envelope with a pair of spaced apart electrodes, a pair of external terminals connected to said electrodes and adapted for connection to a source of intermittent lamp supply current that supplies current for a time period of W seconds followed by an off period of R seconds at least as long as the time interval W, the pressure in the discharge space being at least 4 Torr and high enough to satisfy the condition Tau E< Tau D, the lamp supply frequency being restricted to a range of frequencies such that W/(W+R) <0.4 and the time period W+R lies between 2 pi Tau E and 2 pi Tau D wherein: Tau E is the energy relaxation time (in seconds) of the electrons in the lamp discharge space and Tau D is the diffusion time (in seconds) of the electrons in the lamp discharge space.