High frequency inductive lamp and power oscillator

Details High frequency inductive lamp and power oscillator High frequency inductive lamp and power oscillator

1999-11-05

2001-11-06

Philogene, Haissa (Department: 2821)

Electric lamp and discharge devices: systems

Pulsating or a.c. supply

Induction-type discharge device load

C315S307000, C315S224000, C315S244000, C315S344000

Reexamination Certificate

active

06313587

ABSTRACT:

1. BACKGROUND
1. Field of the Invention
The invention relates generally to discharge lamps, and more specifically to inductively coupled electrodeless lamps. The invention also relates to novel lamp configurations, coupling circuits, bulbs, heat dissipating lamp head assemblies, RF sources (oscillators), directional couplers, aperture structures, starting aids, and excitation coils for inductively coupled electrodeless lamps. The present invention also relates to an improved electrodeless aperture lamp, and to methods of making and using an electrodeless aperture lamp. The invention also relates generally to a novel high power, high frequency solid state oscillator. The invention further relates to a novel control circuit and method for operating an electrodeless lamp.
2. Related Art
In general, the present invention relates to the types of lamps disclosed in U.S. Pat. Nos. 5,404,076 and 5,903,091, each of which is herein incorporated by reference in its entirety.
Electrodeless lamps are known in the art. Such lamps may be characterized according to the type of discharge they produce. Electrodeless discharges may be classified as either E discharges, microwave discharges, travelling wave discharges, or H discharges. The invention relates to those discharges preponderantly characterized as H discharges.
FIG. 1
is a schematic diagram of a conventional electrodeless lamp which produces an E discharge. A power source
1
provides power to a capacitor
2
. A gas-filled vessel
3
is placed between the plates of the capacitor
2
. E discharges in electrodeless lamps are similar to arc discharges in an electroded lamp, except that current is usually much less in an E discharge. Once breakdown of the gas to its ionized or plasma state is achieved, current flows through the capacitance of the vessels walls between the plates of the capacitor
2
, thereby producing a discharge current in the plasma.
FIG. 2
is a schematic diagram of a conventional electrodeless lamp which produces a microwave discharge. A microwave power source
11
provides microwave energy which is directed by a waveguide
12
to a microwave cavity
14
which houses a gas-filled bulb
13
. The microwave energy excites the fill in the bulb
13
and produces a plasma discharge. In a microwave discharge, the wavelength of the electromagnetic field is comparable to the dimensions of the exciting structure, and the discharge is excited by both E and H components of the field.
FIG. 3
is a schematic diagram of a conventional electrodeless lamp which produces a travelling wave discharge. A power source
21
provides power to a launcher
22
. A gas-filled vessel
23
is disposed in the launcher
22
. The gap between the electrodes of the launcher
22
provides an E field which launches a surface wave discharge. The plasma in the vessel
23
is the structure along which the wave is then propagated.
FIG. 4
is a schematic diagram of a conventional electrodeless lamp which produces an H discharge. Electrodeless lamps which produce an H discharge are also referred to as inductively coupled lamps. Inductively coupled lamps were first described more than 100 years ago. Experiments by J. J. Thomson are described in the article “On the discharge of Electricity through Exhausted Tubes without Electrodes,” printed in the London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, Fifth Series, Vol. 32, No.197, October 1891. More recently, D. O. Wharmby, PhD surveyed the state of the electrodeless lamp art in the article entitled “Electrodeless lamps for lighting: a review,” IEEE PROCEEDINGS-A, Vol. 140, No. 6, November 1993, pages 465 to 473.
Certain aspects of the operation of inductively coupled lamps are well understood and have been characterized analytically, for example, in articles by R. B. Piejack, V. A. Godyak and B. M. Alexandrovich entitled “A simple analysis of an inductive RF discharge,” Plasma Sources Sci. Technol. 1,1992, pages 179-186, and “Electrical and Light Characteristics of RF-Inductive Fluorescent Lamps,” Journal of the Illuminating Engineering Society, Winter 1994, pages 40-44.
Inductively coupled lamps having various bulb and coil configurations are described in U.S. Pat. No. 843,534, entitled “Method of Producing Electric Light.” More recently, inductively coupled lamps having novel excitation coils are described in U.S. Pat. Nos. 4,812,702, 4,894,591, and 5,039,903 (hereinafter, “the '903 patent”).
As shown in
FIG. 4
, one example for a conventional inductively coupled lamp includes a low frequency power source
31
providing power to a coil
32
which is wound around a gas-filled vessel
33
. The alternating current around the coil
32
causes a changing magnetic field, which induces an electric field which drives a current in the plasma. In effect, the plasma can be analyzed as a single turn secondary to the coil
32
. See Piejack et al., referenced above. An H discharge is characterized by a closed electrical field, which in many examples forms a visible donut-shaped plasma discharge.
Other geometries have been disclosed for inductively coupled lamps. For example,
FIG. 1
of the Wharmby article set forth examples (a)-(e), including a high inductance coil wound on a ferrite toroid, internal (or optionally external) to the bulb. See Wharmby at p. 471.
As used herein, “low frequency” with respect to an inductively coupled lamp is defined as a frequency less than or equal to about 100 MHz. For example, a typical operating frequency for conventional inductively coupled lamps is 13.56 MHz. For example, the '903 patent discusses an operating frequency range of 1 to 30 MHz, with an exemplary operating frequency being 13.56 MHz. Most, if not all, of the developments relating to known inductively coupled lamps provide lamps operating at low frequency (i.e. less than or equal to about 100 MHz).
Referring again to
FIG. 4
, during the starting operation of an inductively coupled lamp, an E field ionizes the fill in the gas-filled vessel
33
and the discharge is initially characteristic of an E discharge. Once breakdown occurs, however, an abrupt and visible transition to the H discharge occurs. During operation of an inductively coupled lamp, both E and H discharge components are present, but the applied H discharge component provides greater (usually much greater) power to the plasma than the applied E discharge component.
As used herein, “high frequency” with respect to an electrodeless lamp is defined as a frequency substantially greater than about 100 MHz. The prior art describes electrodeless lamps operating at high frequency, including lamps exhibiting coil structures. However, none of the “high frequency” electrodeless lamps in the prior art are, in fact, inductively coupled lamps.
For example, U.S. Pat. No. 4,206,387 describes a “termination fixture” electrodeless lamp which includes a helical coil around the bulb. The “termination fixture” lamp is described as operating the range from 100 MHz to 300 GHz, and preferably at 915 MHz. As noted by Wharmby, “termination fixture” lamps have a size-wavelength relationship such that they produce a microwave discharge, not an inductively coupled discharge.
U.S. Pat. No. 4,908,492 (hereinafter “the '492 patent”) describes a microwave plasma production apparatus which includes a helical coil component. The apparatus is described as operating at 1 GHz or higher, and preferably at 2.45 GHz. As disclosed, however, the coil need not be terminated and a large diameter, multi-turn coil is preferred to produce a large diameter plasma. In such a configuration, the dimension of the exciting structure is comparable to the wavelength of the microwave frequency power and the discharge appears to be a travelling wave discharge, a microwave discharge, or some combination thereof. In any event, the resulting structure apparently does not operate by inductive coupling.
U.S. Pat. No. 5,070,277 describes an electrodeless lamp which includes helical couplers. The lamp is described as operating in the range of 10 MHz to 300 GHz, with a preferred operatin

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