Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Periodic switch in the primary circuit of the supply...
Patent
1989-03-17
1991-01-29
LaRoche, Eugene R.
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Periodic switch in the primary circuit of the supply...
315 3951, 315207, 315283, 331 87, 331 88, H05B 3702
Patent
active
049889222
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a microwave generating system including a magnetron and a power supply circuit therefor, which is adapted to supply microwave energy to a microwave discharge light source, including an electrodeless bulb.
BACKGROUND ART
In recent years, microwave discharge light source having an electrodeless bulb disposed in a microwave resonance cavity has been developed and is attracting attention because of its long life. FIG. 1a shows one of such microwave discharge light source apparatus disclosed in Japanese Laid-Open Patent Application No. 56-126250; FIG. 1b shows a modification thereof disclosed in Japanese Laid-Open Patent Application No. 57-55091. In both apparatuses, a magnetron 1 having an antenna 1a is disposed at the end of a waveguide 2 having ventilating holes 2a which supplies the microwave generated by the magnetron 1 to a resonance cavity 3 through a microwave supply port 3a; the cavity 3 is formed by a paraboloidal wall 3b having a light reflecting rotationally symmetric inner surface and a metallic mesh 3c forming the front face of the cavity 3, which opaque to microwave but transparent to light. A spherical electrodeless discharge bulb 4 disposed in the cavity 3 and having encapsulated therein a plasma generating medium emitts light through the metallic mesh 3c covering the front face of the cavity 3, when the microwave is radiated into the bulb 4: at first, the gas enclosed in the bulb 4 undergoes discharge due to the microwave radiated into the cavity 3; thus, the inner surface of the bulb 4 is heated, and the metal, such as mercury, deposited on the inner surface of the bulb 4 is evaporated into a gas; as a result, the discharge in the bulb 4 goes over to that of the metallic gas, in which light having an emission spectrum peculiar to the kind of the metal is emitted from the discharging metallic gas. The emitted light is reflected by the cavity wall 3b and is radiated forward through the front mesh 3c. The apparatuses further comprise a fan 5 at the end wall of the housing 6 for cooling the magnetron 1 and the bulb 4.
Microwave discharge light source apparatuses similar to those described above are also disclosed in U.S. Pat. Nos. 4,498,029 and 4,673,846, both issued to Yoshizawa et al. The first of these U.S. Patents teach an apparatus in which the bulb is sufficiently small to act substantially as a point light source; the second teach an apparatus in which the wall surface of the microwave resonance cavity having the electrodeless bulb disposed therein is mostly constituted by a mesh, wherein the wires constituting the mesh are electrically connected each other without any contact resistance.
A conventional power supply circuit for a magnetron is disclosed in Japanese Laid-Open Utility Model Application No. 56-162899, or in the first of the above mentioned U.S. Patents, according to which a commercial voltage source at 50 to 60 Hz is coupled to a step-up transformer, and the resulting stepped-up high-voltage AC current is rectified by a full-wave rectifier circuit to obtain pulsing unidirectional current which is supplied to the magnetron. As the rectification is effected by a full-wave rectifier circuit, the resulting high voltage rectified current pulsates at 100 to 120 Hz; consequently, the magnetron generates a microwave pulsing at 100 to 120 Hz. Thus, when magnetron 1 is supplied by this conventional circuit, the discharge in the bulb 4 is caused by the microwave pulsing at 100 to 120 Hz.
The disadvantage of this type of conventional power supply circuit is as follows. First, as the commercial AC voltage of relatively low frequency, i.e., 50 to 60 Hz, is directly supplied to the primary winding of the step-up transformer to obtain a high voltage needed to supply the magnetron, the transformer should be provided with a heavy iron core; the weight of the transformer is equal to or greater than 10 kg when the input power to the magnetron is 1.5 kW. Second, as a full-wave rectifier circuit is used to rectify the AC current induced in the se
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Iwata Akihiko
Kodama Hitoshi
Magome Kazuo
Shoda Isao
Taki Masakazu
LaRoche Eugene R.
Mitsubishi Denki & Kabushiki Kaisha
Yoo Do Hyun
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