Emergency Light for Portable Use. Note Charger and Battery not Shown. Design from Ludens
12 Volt fluorescent lamp drivers
: Three schematics of 12 V drivers for 2, 8 and 20 Watt, plus a lot of explanations about fluorescent tubes. Use the drivers for camping, emergency, boating, etc.
Improper Design of Magnetics or Testing at low voltages can damage the switching NPN. The NPN must have fast switching time, see towers for Cob in pF and .fT in MHz. This may Oscillate for 100 kHz so it has to switch fast, then less heating and better beta at high freq. Choose such a NPN.
The Ic or max current of the NPN can be few times above the current consumption you have planned with the gadget. As a thumb rule if this is a 10W at 10V that means 1 Amp current. Hence choose a device 5 times above 1 A. Use a 5 A device or a 7 A for reliability.
The voltage selection of NPN must also take into account the transients in the switching. If its a sine oscillator like above, the transients, spikes are mild but in square wave switching, the spikes can be very sharp on resonance. These low energy zaps can weaken the NPN and deteriorate its switching and cause heating and eventual failure. So many CFL lamps and Emergency Light's fail quickly as they are not built robustly.
Even this circuit above is good only if is built very carefully.