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[TCML] A Small SSTC for Fluorescent Lighting



A Small Solid State Tesla Coil for Fluorescent Lighting

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Fig. 1.  A solid state blocking oscillator.

The ballast coil is wound on a 1/2" I.D. form rolled from a 9" long piece of plain unlined writing paper fastened with white glue. The final dimensions of the tube should be: 17/32" O.D., x 2" length. If the wooden dowel that is used to create the form is also used to hold the form in the winder, it should be finely sanded and rubbed with paraffin in order to ease the removal of the completed coil.

All of the windings are started on the left and proceed to the right. They are identified as Ss (short Secondary), P (Primary), and Sl (long Secondary). The first coil wound on the form is the single layer short secondary. This is followed by the single layer primary and finally the long multiple layer secondary. In order to adhere to the specifications, the individual turns of the first two windings, i.e. Ss and P, are counted for the number of turns. The 30 gauge wire that will make up Sl is measured for length. Each coil is held in place with a single layer of 2" masking tape extending about 1/4" beyond the ends of the coil and pressed down on to the left and right ends of the form. When winding the long secondary, an ordinary adhesive "glue stick" is used to fasten the last few turns of each course in place. Tape is not placed between the multiple layers of the long secondary.

Notice the tapered appearance at the ends of the completed coil assembly (see fig. 2d). This is achieved by reducing the number of turns on each layer of the long secondary as the winding progresses. Generally speaking, each layer of the long secondary has about three fewer turns than the previous layer. Upon reaching 133rd or 134th foot of wire, the turns spacing is spread out so the last turn will line up with the coil's right end. Be sure to add about 8 inches of wire for the lead-ins (4" at each end). As a preventive measure against insulation failure, stick a small piece of tape, about 3/16" x 1/2", to the right end of Sl to better isolate the 30 gauge lead-in wire from the lower windings. The finished coil is covered with one last piece of 2" tape wrapped all around and pressed in place. When you are done, mark the completed assembly on its left end to assure correct installation on the circuit board. The marked or left end of the coil should be positioned toward the bottom of the circuit board as it appears in fig. 3 (notice the large asterisk printed on the board).

The specifications for the three windings are as follows:

Short secondary: 70 turns of 24 gauge, 1 1/2" long, close wound.

Primary: 44 turns of 20 gauge, 1 1/2" long (or as close to this as possible), close wound.

Long secondary: 678 turns (approx.) of 30 gauge, 6 layers close wound plus 1 additional pass from left to right across the face of the coil to use up remainder of wire needed to achieve a total wire length of 135 to 140 feet. (Spread out the last 10 turns so the very last turn ends up at the right end of the coil.) A 135 ft. secondary seems to provide slightly more efficient operation while a longer one provides more rapid striking or starting of the fluorescent tube.

A cylindrical ferrite core of the AM radio loop stick antenna type, approximately 2 3/4" x 3/8", is held in position within the coil form by rolling it in a 2" x 11" piece of paper towel and fastening everything in place with a few dabs of white glue.

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Fig. 2. The RF transformer assembly as each of the three windings is put into place.

Fig, 2a. shows the short secondary in place. Fig. 2b. shows the same winding covered with tape with the lead in wires repositioned. In fig. 2c. the primary is being wound over the previous winding. Fig. 2d. shows the 6+ layers of the long secondary in place and not yet covered with the final layer of tape. Notice also the small piece of tape that isolates the lead-in from the right end of the completed coil.

Component Values for the F15T12 Fluorescent Tube Type

D1 1N5400
C1 100 µfd., 25 V Electrolytic Capacitor
C2 .1 µfd. Mylar Film Capacitor
C3 none
R1 68 ohm, 1/2 W
R2 330/470 ohm, 1/4 W
R3 1200/470 ohm, 1/4 W
Q1 TIP 31 NPN Power Transistor

Component Values for the F48T12 Fluorescent Tube Type

D1 1N5400
C1 100 µfd., 25 V Electrolytic
C2 .05 µfd.
C3 .0015
R1 100 ohm, 1/2 W
R2 330 ohm, 1/4 W
R3 1200 ohm, 1/4 W
Q1 TIP 31

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Figure 3. The circuit board as viewed from the component side (for component placement only).

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Figure 4. The 2" x 4" printed circuit board, viewed from the foil side.


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