Tiny high voltage converter
Disposable camera's with flash contain a host of useful components. The
flash tube is nice, the pulse capacitor and a 1.5V to 300V transformer.
If you remove the trigger circuit, pulse cap and flash tube you get a
nice high voltage converter. Only component you need to add is a
smoothing capacitor. I REALLY
suggest you do not use the photoflash capacitor for this, its way to
big and absolutely positivly leathal!
Replace the capacitor by a more sane value like 10uF. Still i
accidentally grabbed the cap side, i can tell you it is not a pleasant
feeling. Be careful as this thing is going to charge up to a lot of
power.
This is the original PCB that was in the disposable camera, the top
part contains a small transformer, a base resistor and a low saturation
high current transistor in a TO-92 housing. Most of the transistors
used in these kind of circuits have a UCE of about 10V and high Hfe.
First you remove the capacitor, the battery clips, flashtube and the
trigger circuit (220nF capacitor, a 4.7Mohm resistor, pulse transformer
and a trigger switch). Find the recitifying diode and place a smoothing
capacitor over it. I used a 10uF 450V capacitor that i also used for my
high voltage switching powersupply. I reused the 4.7Mohm resistor as a
bleeder resistor for the capacitor as a safety. When you are done
modifying the board you end up with something below.
Here you see a closeup on the board. The black part underneath the
capacitor is a high speed, high voltage rectifier that was already
there. I removed most of it on the right of it, except the LED and LED
series resistor. It provides a good indication that your circuit is
live and working so it was left in place. For a low cost circuit this
LED seems of the high brightness type, this is probably becouse the led
had to shine trough a light pipe in the camera to provide a indication
if the flash was ready. The holes of the flash capacitor have been
reused for the connection block with screws, providing a safe way to
attach wires to it.
Here you see the whole deal in action, a neon bulb has been put in
series with a 100k resistor to limit the current to the bulb. If you
connect the supply directly over the bulb you get spectaculair flashes
from the bulb as the smoothing cap charges up, and the discharges in
the bulb instantly. This also clouds the bulb and i assume its not too
healthy for the bulb.
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Last update at: 16-08-2005