20 Watt Inverter

This circuit will drive a 40 watt fluorescent or two 20-watt tubes in series. The transformer is wound on a ferrite rod 10mm dia and 8cm long. The wire diameters is 0.61mm wire for the primary and 0.28mm wire for the secondary and feedback winding.

The circuit will take approx. 1.5amp on 12v, making it more efficient than running the tubes from the mains. A normal fluorescent takes 20 watts for the tube and about 15 watts for the ballast.


Note: Do not remove the tube when the circuit is operating as the spikes produced by the transformer will damage the transistor.

Parts list

  • Transistor – BC338 and TIP 3055
  • Resistance – 47 K, 47 R, 180 R, 2R2
  • Variable Resistance – 100k
  • Capacitors – 100u 16v, 100n
  • On/Off Switch
  •  1 ferrite rod 10mm in 8mm long
  • 30 m winding wire .28mm dia
  • 4 m winding wire .61mm dia
  • 2* 20 watt tube or 1* 40 watt tube
  • 12 v DC power supply

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