Electric lamp and discharge devices: systems – Combined load device or load device temperature modifying... – Discharge device load with distributed parameter-type...
Reexamination Certificate
2001-01-19
2001-11-20
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Combined load device or load device temperature modifying...
Discharge device load with distributed parameter-type...
C315S248000, C315S344000
Reexamination Certificate
active
06320316
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to apparatus for coupling power into a body of gas by induction to provide a gas discharge, comprising a source of a/c power coupled to a circuit arrangement having an inductor comprising a plurality of turns of a conductor surrounding a space having a body of gas. It relates particularly, though not exclusively, to coupling of a/c power at radio frequencies.
2. Background
Radio frequency gas discharges are used in a variety of technical fields such as lighting and thin film deposition and etching. Drive circuits for such gas discharges normally have a coupling inductor as part of a series tuned circuit including a series capacitor. The circuit is driven at its resonant frequency to produce the high voltage required to strike the discharge. After striking the discharge, current in the inductor couples into the conducting gas plasma by transformer action (i.e. inductively), the plasma thus loading the resonant circuit and reducing the resonant voltage.
The series capacitor which is used in such drive circuits to complete the tuned circuit introduces several drawbacks. For example, to strike the gas discharge or plasma, high voltages such as, for example, several thousand volts may be encountered. Low cost capacitors have a significant temperature dependence at such voltages, which can cause the resonant frequency to change. The placement of the capacitor can be problematical because of the danger of breakdown of the printed circuit board. In addition, the resonant node on the side of the capacitor connected to the coil constitutes a “hot” end to the coil, increasing the problem of r.f. radiation in operation.
A known apparatus for coupling power into a body of gas and minimising the problem of r.f. radiation is disclosed in U.S. Pat. No. 5,525,871
SUMMARY OF THE INVENTION
According to the present invention, there is provided apparatus as defined in claims 1-4. This arrangement avoids the problems associated with a separate series capacitor by using the mutual capacitance between two adjacent coils, and can minimise unwanted r.f. radiated energy.
REFERENCES:
patent: 4710678 (1987-12-01), Houkes et al.
patent: 4918031 (1990-04-01), Flamm et al.
patent: 5726523 (1998-03-01), Popov et al.
patent: 0790635-A2 (1997-08-01), None
patent: 10149898 (1998-06-01), None
Bollman William H.
Central Research Laboratories Limited
Vu David
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