This one’s a beauty. It will drive multiple CFLs without the
need for heatsinks on the MOSFETs. Fit heatsinks and you can run even more, up
to a total of 100W.
Fig.1: an SG 3525 pulse width modulator chip running at 85kHz drives two MOSFETs and a stepup transformer to develop 350V DC to drive compact fluorescent lamps (CFLs) or a small colour TV set.
However, the real bonus is that you don’t have to wind the
transformer – a tricky job at the best of times. This kit comes with a pre-wound
transformer so all you have to do is to solder it into the PC board.
As pictured, the prototype inverter is running four 11W CFL
tubes and the MOSFETs are barely warm. And to do that it is drawing just 3.2A
from a 12V battery so it is a pretty efficient device.
CAUTION: DANGEROUS VOLTAGES
The output from this inverter is around 350V DC and is thus as dangerous as mains voltages. Handle with care - never work on the circuit with power applied. The finished project should be installed in a plastic case.
It’s compact too, housed on a PC board measuring 83 x 50mm and
standing about 58mm high because of the on-board transformer.
The circuit is quite simple, as shown in Fig.1 and is based on
an ST SG3525 regulating pulse-width modulator (IC1) which drives a couple of
Mosfets and the push-pull stepup transformer.