[TCML] A Small SSTC for Fluorescent Lighting

[Gary Peterson]

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.