A 40 watt fluorescent (tube lamp, TL) or two 20-watt tubes in series will be driven by this circuit. The transformer is wound on a ferrite rod 10mm dia and 8cm long. The diameters of the wire are not critical but our prototype used 0.61mm wire for the primary and 0.28mm wire for the secondary and feedback winding.
When circuit is operating as the spikes produced by the transformer will damage the transistor, do not remove the tube. The circuit will take approx 1.5 amperes on 12v, making it more efficient than running the tubes from the mains. A normal fluoro takes 15 watts for the ballast and 20 watts for the tube. [Circuit’s schematic diagram source: talkingelectronics.com]