Solid state RF light driver for electrodeless lighting

#1. Field of the Invention

#This invention relates generally to apparatus for exciting a light source and more particularly to solid state driver circuitry for exciting a high intensity electrodeless light bulb.

#2. Description of Related Art

#The present invention will become more fully understood from the detailed description provided hereinafter and the accompanying drawings which are provided by way of illustration only, and thus are not meant to be limitative of the present invention, and wherein:

#FIG. 1 is an electrical schematic diagram illustrative of the preferred embodiment of the invention; and

#FIG. 2 is an exploded diagram illustrative of means used for cooling the embodiment shown in FIG. 1.

#Referring now to the drawings and more particularly to FIG. 1, reference numeral 10 denotes a field effect transistor having gate (g), source (s), and drain (d) electrodes, and more particularly a silicon carbide static induction transistor (SIT) which is capable of operating at S-band frequencies. Such a device has been developed by the present assignee and comprises a transistor which is significantly superior to prior art devices fabricated, for example, on silicon or gallium arsenide, particularly as it pertains to power, gain, operating voltage, efficiency and temperature tolerance. The details of a silicon carbide static induction transistor are furthermore disclosed in the above cross referenced related applications as well as U.S. Pat. No. 5,612,547.

#The SIT 10 is powered by a DC supply voltage generated by a full wave rectifier bridge 12 which is connected to an AC power line voltage (120 VAC) shown in FIG. 1 applied across a pair of AC terminals 14 and 16. The DC output voltage from the bridge 12 is filtered by means of an L-C filter consisting of a series inductor 18 and a parallel capacitor 20 connected across a pair of output terminals 19 and 21. A pair of supply voltage leads 22 and 24 are connected across the capacitor 20, lead 22 being a positive (+) potential lead, while supply lead 24 is a reference or ground lead. The DC voltage which appears across leads 22 and 24 is from about 170 VDC at no load but drops down to about 108 VDC when loaded by the circuitry shown in FIG. 1. A SIT 10 used in connection with this invention has a nominal operating voltage of 108 V DC but has the capability to withstand transient voltages above 170 V DC. This occurs because silicon carbide S-band SITs can typically operate in the 80-100 V range, while having a breakdown voltage up to 350 V DC. This voltage capability can be increased as required for use with a transformerless power supply.

#The SIT 10 as shown in FIG. 1 operates as a power oscillator by virtue of having its gate electrode (g) connected to the ground side lead 24 by means of an inductance reactance element 26, while the source (s) electrode is coupled to the ground side lead 24 by means of a length of stripline microwave transmission line 28, which acts as an impedance matching element, and a series connected frequency determining element 30, shown comprising a variable capacitive reactance. However, when desirable, the frequency determining element may be comprised of a resonator structure or crystal, not shown. The drain (d) electrode is connected to the power supply lead 22 by means of another length of stripline 32, which also acts as an impedance matching element, and a choke coil 34. The oscillator 35 configuration shown in FIG. 1 preferably operates at a frequency of 2450 MHz and can output, for example, at between 50 and 100 Watts of continuous (CW) power. A frequency of 900 MHz can also be implemented simply by changing component values in a well known manner.