Miracle of Miniaturization - The Built-In Camera Flash
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Left, the core of a camera flash transformer
and one of the legs which broke off. Right, a #2 pencil.
Built-in camera flashes aren't something people think about much.
Almost every modern camera has one. They make the little
whining sound and blind us. Brighten up our pictures. After
all, they've been around for years. But the fact is there's very
little space left inside that camera with all the film and mechanical
workings. An entire electronic circuit has to be squeezed in
there.
With all the miniaturization that's been going on in the computer and
electronics industry, it's easy to be underwhelmed by this; but just
stop and think about it for a minute. We aren't talking about
data signals which only require tiny amounts of electricity and which
the mere presence or absence of is enough to perform their function.
That flash of light is produced by raw power.
Let's take a moment to briefly summarize the operation of the camera
flash. 1 or 2 batteries, usually AA give us around 1.5-3 volts
and plenty of power. The problem is that this power can only be
released slowly over time, and worse yet, we need 330 volts to produce
our electrical arc (flash) and 3,000 volts to get it going! The
first problem is easily fixed by using a capacitor, but the second is a
bit more complicated. That's where our circuit comes in.
There's a transistor oscillator and a transfomer to get our 330
volts to charge the capacitor. This is what makes the whining
sound we hear. There's also another smaller capacitor which is
charged at the same time which is dumped onto another transformer when
you press the shutter button to give us our 3,000 volt "tickler".
The flash we see is actually an electrical arc inside of a glass
tube filled with xenon gas because it gives a whiter arc than air does.
Now, believe it or not, it's not the 3,000 volt transformer which is
the problem. That one only has to step from 300 up to 3,000
volts, a mere 10:1 ratio. It's the other one, the 1.5 to 330 volt
step-up transformer, which must produce a ratio of 220:1 or more, which
is the real problem. Now when you think of a transformer, you
usually think of the one you might use to plug in your answering
machine or a cordless razor. But could you imagine a transformer
of this size inside your camera? It would almost double the size
and certainly double the weight. The tiny transformer inisde your
camera is an incredible device indeed.
In the photo above, you can see the core of a built-in camera flash
transformer next to a pencil. On this particular core was 6 turns
of fine wire around 30AWG, which is the primary, 10 turns of finer wire
for the feedback, and for the secondary, an incredible 1,310 turns of
wire which can only
be described as microscopic. When still on the transformer, it
just looks like a solid coppery piece. The individual windings
can only be seen under a microscope. It's so fine that if a
single strand is laid down onto a surface, it just disappears. They are even finer than some hair.
Wire from the secondary next to standard 12AWG house wiring, and the tip of the same pencil.
Transformer windings can't be made like semiconductors - by
photographic or chemical methods. They have to be wound.
This is usually done on winding jigs, but the ends still have to
be attached by hand. This labor intensive process is performed
mostly in Mexico or other third world countries in order for it to be
cost-effective. Otherwise, they wouldn't be so affordable.
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