"petrus bitbyter" wrote in message
.nl...

"P E Schoen" schreef in bericht
...
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

This is good to know. Those little circuits in each CFL have a lot of good
components, including a DIAC and high voltage transistors, and it's
probably
possible to use them to drive small fluorescent lamps for DIY projects or
repair. I doubt they could be used for the 40W tubes, but a driver from a
100W CFL should work on a 20W tube such as are in many desk lamps and
small
kitchen fixtures.

Does anyone know if there is any problem with this?

Thanks,

Paul

PS: GO RAVENS!!!!!

The traditional way of igniting TLs is first heating the heaters and then
start it with a relative high voltage puls. But heating first is not
necessary. The lamp will ignite if only the voltage of the ignition pulse
is high enough. Nevertheless, the heaters cannot be omitted as they
provide the electrons required for the current through the tube.
Especially low power TLs are sometimes ignited this way. When used with
low frequencies i.e. 50Hz or 60Hz, it is said to shorten the lifetime of
the tube. The circuit I ever found in a handheld 8W TL lamp did work but
gave a flickering light.

I also use a magnifier lamp but a bigger one containing a 22W circline. It
came with an old-fashioned iron ballast and no starter. I had to start it
by hand using the special switch. That is I had to push the button and
keep it pushed for a 6s. During this time the heaters were on. Relieving
the button ignited the lamp... Most of the times. But over time igniting
failed more and more and the circlines seemed to worn out faster and
faster. Investigating revealed the special switch to be worn out beyond
repair. So I got a 20W CFL, got out the electronics, put them in a box and
connected it to the circline. Works fine for several years now already.

Don't forget the significant increase of efficiency running the tube at
around 20kHz.

Frequency may also contribute to easier starting, although most CFLs seem to
have some sort of setup to run power into the heaters.

More often than not its a capacitor to bleed some of the AC current via the
heaters, some Ikea branded CFLs I got from a car boot sale long ago had
resin dipped double pellet thermistors bridging the heaters across the tube.