Pic of inside of small twisted fluor bulb (cool)

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MrAl
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Pic of inside of small twisted fluor bulb (cool)

Post by MrAl » Fri Dec 22, 2006 10:17 am

Hello,

One of my small twisted fluor bulbs went out so i got out the dremel
and cut into the base to extract the circuit. It turned out to be
pretty interesting, and many more parts than i expected to find...

http://hometown.aol.com/xaxo/page12.html
LEDs vs Bulbs, LEDs are winning.

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haklesup
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Post by haklesup » Fri Dec 22, 2006 11:09 am

I've broke a few of those myself and have occasionally wondered what the output specs on that ballast are and if it could be useful for anything else.

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Chris Smith
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Post by Chris Smith » Fri Dec 22, 2006 1:30 pm

I have about a dozen ready for experiment.

Mine seem to be FETS switching the power and a ballast start circuit.

I want to replace some FETs with huge ones and try some four foot tubes.

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MrAl
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Post by MrAl » Fri Dec 22, 2006 4:50 pm

Hi again,

Chris, what are they the more modern kind?
Mine i think is maybe 5 to 7 years old and the tube is
'folded' back and forth. I suspect the newer ones
use less parts, but now im tempted to open one up and
have a look, he he.
LEDs vs Bulbs, LEDs are winning.

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Chris Smith
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Post by Chris Smith » Fri Dec 22, 2006 5:40 pm

I have to look at mine a lot closer but the last one I opened didnt have any transformers etc, were really tiny in the parts count, and it looked like fets were doing all of the work using some kind of hight speed timing.

Mine are about 2 years old.

Great experiment come summer or any thing but these minus temps?

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Post by hp » Fri Dec 22, 2006 6:40 pm

I opened up a modern-ish one before and they seem to use specialized driver ICs and one or two fets. I'll have to see if I can find the pcb and see what chip it used.

Harrison

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Post by jimandy » Fri Dec 22, 2006 7:06 pm

Doesn't it generate a high voltage to make the vapor flouresce?
"if it's not another it's one thing."

rshayes
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Post by rshayes » Fri Dec 22, 2006 7:19 pm

That looks very close to the one I opened up and traced a year or so ago.

The circuit was a totem pole arrangement of two transistors driving a series tuned LC circuit with a capacitor in series with the tube as a ballast. The base drive was a current transformer in series with the output with separate secondary windings for driving each transistor.

Your board seems to have the same parts. The output inductor is probably the part which looks like a transformer using ferrite E-cores. The feedback transformer is probably the green toroid just above it.

From the size of the parts, I would guess that the frequency is in the several hundred kilohertz range.

I would be suprised if the circuit is in operating order. The design looks marginal and I would not be surprised if most of the failures of these bulbs were circuit failures rather than failures of the fluorescent tubes.

The transistors would have to have a minimum collector voltage rating in above 200 volts and a collector current rating of a few hundred milliamps or more. That is a little unusual, and they might be worth salvaging if they are still good. The cores for the magnetic parts are probably still good and could be rewound. The winding insulation seems to be mainly the enamel on the wire, and this is another thing that would be prone to failure at stresses of several hundred volts. The diodes seem to be similar to 1N4007's. These are so cheap new that I wouldn't try to reuse salvaged ones in any serious project.

With different capacitor and inductor values, the circuit might be useful for driving an ultrasonic cleaner.

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MrAl
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Post by MrAl » Sat Dec 23, 2006 3:06 am

Hi again,

Yes the device is a converter that produces a high frequency
at fairly high voltage to drive the tube.

I didnt check the whole circuit but i noticed that
the two transistors are arranged as a half bridge, driving the
output through another coil and caps. The coil appears
to be 6mH, which is quite large.
Apparently they first produce 340vdc by using two half wave
rectifiers, one for +170v and the other for -170v, which
is filtered by two caps (one for each) so the total across the
two caps could be 340vdc.
And yes, the toroid is the driver, driving the bases of the
two transistors through two 20 ohm resistors.
They use another choke to filter the line, as well as a rather
large cap (the big rectangular yellow thing) value 0.1uf and
rated 250vac to help prevent back emi.

Perhaps if i get the time i'll trace out the whole circuit.

I wouldnt mind building an off line dc converter to generate
four 10 amp power supplies about 2v each, for charging NiMH.
I looked at other ways of doing it but four 10 amp supplies
means a transformer rated for 40 amps, which is rather large
for the 60Hz type. The supplies would have to be isolated too
for safety reasons.
LEDs vs Bulbs, LEDs are winning.

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