"P E Schoen" wrote in message
...
I have a desk lamp, with a magnifier and a 12W T4 circline fluorescent
bulb, that I use constantly for working on PCBs and electronics projects
in general. I bought it several years ago and recently it started
flickering and then died. I replaced the bulb, but still no joy, and after
replacing the blown fuse and two damaged transistors, I found that the
little transformer had an open winding.

So, I thought, a 60W equivalent CFL is actually about 11-13 watts, and the
little circuit in them should work. I had a couple of broken or dead bulbs
ready for recycling, so I opened the bases, cut the leads, and extracted
the PCBs. After a few unsuccessful tries, I was able to get it to work and
now my lamp is once again operational.

I found some schematics of the CFL driver boards he
http://www.pavouk.org/hw/lamp/en_index.html

Some of those circuits matched what I had almost exactly. It was a little
difficult to follow the explanation of how they operate, but what was
confusing is the four pins shown on the lamp itself, which is also how the
bulbs are made. I assume they are the heaters that are usually activated
with a starter, but I did not find any continuity on those pins. The desk
lamp only had one wire to each of two pins on the circline bulb, but in
the CFLs all four wires were connected to different points on the PCB. It
would only work when I shorted the connections that would have gone to the
heaters, and it seems to work very well. It starts to light at 50 VAC and
reaches full brightness at 100-120V, at which it draws about 100mA. That's
close enough to 12 watts for me!

Here's a little clip of my repair project:
http://www.youtube.com/watch?v=e7QJQ...ature=youtu.be


Many CFL PCBs have a diac - you can make a neat little pulsed bicycle light
using a blocking oscillator inverter to charge a 47u electro. Everytime it
reaches about 32V, you have the diac dump the charge into the LED bank of a
cheap & nasty LED worklight.

My project was published in Elektor a year or two ago.