An electrodeless lamp circuit with a coil surrounding a krypton lamp is driven by an RF input source. A coil surrounding a mercury lamp is tapped across the connection of the input central to the krypton-lamp coil. Each coil is connected in parallel with separate capacitors which form resonant circuits at the input frequency

Clough, L. G.

Laue, H. H.

English

NASA Technical Reports Server

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ATTN OF: GP
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
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AUG 7 1973
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Copy of patent cited above
https://ntrs.nasa.gov/search.jsp?R=19730021449 2020-03-17T09:06:38+00:00Z
United States Patent
Fletcher et al.
tin 3,745,410
[45] July 10, 1973
[54] DRIVING LAMPS BY INDUCTION
[76] Inventors: James C. Fletcher, Administrator of
the National Aeronautics & Space
Administration with respect to an
invention of; Helntuth H. Laue,
Escondido; Leonard G. Clough,
Poway, both of Calif.
[22] Filed: Mar. 16, 1972
[21] Appl. No.: 235,269
[52J U.S. Cl 315/248, 313/161, 315/324
[51 ] Int. Cl HOSb 41/16
[58] Field of Search 315/248, 324;
313/161
[56] References Cited
UNITED STATES PATENTS
3,323,010 5/1967 Bisjak et al 315/248 X
3,230,422 1/1966 Gourber et al 315/248 X
3,196,312 7/1965 Marrison 315/248 X
2,347,715 5/1944 Spencer 313/161
Primary Examiner—Alfred L. Brody
Attorney— L. D. Wofford, Jr.. George J. Porter and
John R. Manning
[57] ABSTRACT
An electrodeless lamp circuit with a coil surrounding a
krypton lamp driven by an RF input source tapped
across an end part of the coil and with a coil surround-
ing a mercury lamp tapped across the connection of the
input central to the krypton-lamp coil and a point of
the krypton-lamp coil electrically away from both input
connections. Each coil is connected in parallel with
separate capacitors which form resonant circuits at the
input frequency.
4 Claims, 1 Drawing Figure
MERCURY
LAMP 3
50 ARF
INPUT
s
13
KRYPTON
LAMP I
PATENTED JULIO 1973 3.745,410
MERCURY
LAMP 3
50 ARF
INPUT
s
13
15
KRYPTON
LAMP. I
-II
3,745,410
1 2
DRIVING LAMPS BY INDUCTION DESCRIPTION OF THE PREFERRED
ORIGIN OF THE INVENTION EMBODIMENT
The invention described herein was made in the per- The preferred system is a light-weight one of a kryp-
formance of work under a NASA contract and is sub- 5 ton lamp 1 and a mercury lamp 3, suitable for use in a
ject to the provisions of Section 305 of the National laboratory or test environment. The lamps 1 and 3 are
Aeronautics and Space Act of 1958, Public Law essentially conventional in every respect except for the
85-568 (72 Stat. 435; 42 U.S.C. 2457). circuit connections of the driving circuit. Lamp 1 con-
__ . »,^ , ,. .,„ ^ tains krypton and lamp 3 contains mercury, within a
BACKGROUND OF THE INVENTION ,„
 transpa/ePm tube or thelke in accordance wfth conven.
Light-weight, efficient vacuum ultraviolet sources tional designs for such lamps, so that magnetically in-
are needed for various applications. Conventionally, duced energy at radio frequencies will drive the kryp-
two light sources have been used to create two, single ton or mercury into ionization (resonance) and thereby
lines in the spectrum produced, separated by at least produce useful ultraviolet radiation.
300 angstroms. Inductively powered electrodeless 15 Such lamps have previously been designed for lower
lamps have been preferred to eliminate any possibility radio frequency operation when employing increased
of contamination by metal ion emissions. wire size, coil diameter, and wire shape to promote
Self-starting and low power requirements to sustain heat dissipation.
light emission are particularly desired criteria for such Coil 5 surrounds krypton lamp I in electrically induc-
a system. The total system in which the light production 20 tive relationship for driving lamp 1. (Although only a
would be a part is particularly useful for experiments section of lamp 1 is illustrated in the drawing, it will be
and the like in extraterritorial space. understood, of course, as is conventional, that lamp 1
Existing methods of driving those electrodeless lamps extends within all or substantially all of coil 5.) Capaci-
into resonance (or ionization) have required heavy tor 7 is connected electrically across coil 5 and is of
power supplies and large amounts of AC power. In 25 magnitude to form a resonant circuit at the frequency
many cases, high frequency medical microwave power of the input power when lamp 1 is ionized and is
generators were employed which produced high power, thereby producing the desired output radiation,
up to 100 watts carrier wave. Similarly, coil 9 surrounds mercury lamp 3 in electri-
The present invention employes an autotransformer cally inductive relationship for driving lamp 3. (As with
arrangement in a circuit with conventional electrode- 30 respect to lamp 1, lamp3, although only apart is shown
less lamps and other electrical elements. A similar use in the drawing, actually is located within all or substan-
in the prior art of an autotransformer design or the like tially all of coil 9.) Capacitor 11 is connected electri-
is not known. cally across coil 9 and is of magnitude to form a reso-
~ ^..^ , ,„,. _., nant circuit at the frequency of the input power when
SUMMARY OF THE INVENTION
 35 lamp 3 is ionized and4 thereyby producPing the desired
It is an object of this invention to provide an efficient output radiation.
and useful induction lamp driving system. Coil 9 is connected electrically to one line 13 of the
It is a more specific object of this invention to pro- input power and to a point on coil 5 spaced electrically
vide a small or light-weight induction lamp driving sys- from the line 13 and the other input power line IS.
tem. 4^ Mercury is ionized more readily than krypton, and the
It is another object of this invention to provide an in- coil 9 is tapped across coil 5 at a point at which the
duction lamp driving system with reduced power re- proper, smaller voltage is provided.
quirements, both during starting and in operation. Input power to lines 13 and 15 is by a 7 watt, 50 MHz
It is a more general object of this invention to provide radio frequency, 14 mhos supply.
a driving circuit for electrodeless lamps and the like In operation, the radio frequency input power is ap-
comprising circuits made up basically or ordinary coils plied across lines 13 and 15, and the response of the
and capacitors. lamps is automatic in accordance with the natural re-
in accordance with this invention a coil is positioned sponse of the elements and circuits involved. Initially,
to drive an inductively driven lamp, and the power the lamps 1 and 3 are not ionized. Self ignition of the
input to the coil is tapped across the coil generally in lamps occurs a short time later (up to 2 minutes, de-
the manner of an autotransformer. A capacitor is posi- pending on tuning of the overall circuit). After ignition,
tioned across the coil, the capacitor being of magnitude both coils 5 and 9 are in resonant circuit with their as-
to form a resonant circuit with the coil at the input fre- sociated capacitors 7 and 11 respectively, and the reso-
quency. Additionally, in accordance with the more nant operation minimizes power consumption. In the
general aspects of the preferred embodiment, a second preferred embodiment, RF power requirements have
coil is tapped across the first coil at least partially past been brought to below 7 watts.
the part of the first coil which the input is across. The Prior to ignition, the voltage standing wave ratio seen
coil is positioned to drive a second, inductively driven by the RF source is infinite. Mismatch protection of
lamp having characteristics different from the first, and ,~ some kind associated with the power source is there-
a second capacitor is positioned across the second coil, fore required. As soon as the gas in the lamps has ion-
that capacitor being of magnitude to form a resonant ized, the voltage standing wave ratio drops to low lev-
circuit with the second coil at the input frequency. els, the extent depending on tuning of the system. Such
BRIFF DFSrRIPTION OF THE DRAWING rat'°S °f ' "3 l° ' HaVC bee" read''y achievedBRIEF DESCRIPTION F t DRA ING ^
 Thjs system may be categorized as low frequency.
The drawing illustrates the preferred system, in since some driving systems require microwave frequen-
which a krypton electrodeless lamp and a mercury cies, and the lower RF frequency range drivers prefera-
electrodeless lamp are driven simultaneously. bly used with this system are less complex than higher
3,745,410
frequency drivers. The power requirements of this em-
bodiment are greatly reduced, to less than one-fiftieth
of those of comparable prior systems. The total system,
including RF power supply and the like, has also been
weight reduced by at least 50 to 1. The reduced power 5
requirements make readily possible the use of an all-
solid-state driver.
Lamp performance versus temperature has been
studied. Heat sinking or other control appears desir-
able. Spectral response curves obtained with the aid of 10
the McPherson spectrometer indicate that excellent
quality vacuum ultraviolet light is emitted. Modulation
of the light sources utilizing a 50 percent duty cycle
square wave modulated signal further simplified photo
multiplier tube signal processing, and the moduation is
does not impair the spectral purity of the light sources.
It would be possible to connect coil 9 across coil 5 at
points at which the desired capacity is supplied inher-
ently instead of by a separately provided capacitor,
such as capacitor 11. 20
Other variations of the invention described will be
apparent, and variations may well be developed which
employ more than ordinary skill in this art, but never-
theless employ the basic contribution and elements of
this invention. Accordingly, patent protection should 25
not be essentially limited by the preferred embodi-
ments disclosed, but should be as provided by law, with
particular reference to the accompanying claims.
What is claimed is:
1. A system for driving lamps by induction compris-
ing:
a first lamp adapted to be driven for production of
electromagnetic radiation by induction from an
electrical coil;
a first coil positioned to drive said lamp for said pro-
duction of radiation;
first capacitve means electrically connected across
said coil of a magnitude to form a resonant circuit
with said coil when said lamp is being driven and
producing said radiation at a given radio fre-
quency;
a power source operative at said radio frequency
connected across a part only of said first coil;
a second lamp adapted to be driven for production of
electromagnetic radiation by induction from an
electrical coil;
a second coil positioned to drive said second lamp for
said production of radiation;
second capacitive means electrically connected
across said second coil of a magnitude to form a
resonant circuit with said second coil when said
lamp is being driven and producing said radiation
at said radio frequency, said second coil being con-
nected electrically across said first coil at locations
at least one of which is electrically separated from
the part of said first coil across which said power
source is connected.
2. The system as in claim 1 in which said second coil
is connected at locations across said first coil at which
said second capacitive means is inherently supplied by
said first coil and said second coil.
3. The system as in claim 1 in which the radiation
producing material of said first lamp consists essentially
30 of krypton and the radiation producing material of said
second lamp consists essentially of mercury.
4. The system as in claim 3 in which said second coil
is connected substantially across one of said connec-
tions of said power source to said first coil and said
35 electrically separated location.
40
45
50
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60
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Driving lamps by induction

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