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DIY studio strobe

Ah, but how many transistors have you seen with hFE > 30 that do 150A peak

*and* over 400V? Possibly some ISOTOP modules would actually work... it would be quite amusing to see a camera where the flash module is bigger (and more expensive!) than the lens assembly! :-)

The annoying part about BJTs, you can't pulse them much beyond ratings, where hFE goes to zero and Vce(sat) explodes. So you'll end up needing like

150A of base current to make it work, which makes a GTO look a lot better... you still need 150A, but it's only a short pulse.

Even getting 5A from inside a camera would be fairly impressive, let alone

150A, but I suppose that, like the flash itself, it would all be pulsed from some other big cap. Maybe an overrated boost/buck/SEPIC to keep it around 3V while the cap gets sucked out, before the battery can keep it going.

Mmmm, snubbing a 150A BJT, inside a camera... that thing will be bigger than the photoflash cap itself!

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams
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Last time I saw one was on some old Kodak flash. From one of those cameras with the flat type battery pack!

On the other hand, my ex-Canon S1 IS:

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contained an awfully small 220uF 330V electrolytic, attached with impressively thin wires (which I'm guessing are slightly thicker than the film PCB stuff they use for all other connections). On the board are an inverter (or trigger?) transformer, some transistors, capacitors, a diode, and an incredibly small IGBT -- smaller than SO-8, I forget what part number but it's rated at 150A peak, 400V or so, and 4Vce(sat) at 150A -- pulsed, obviously. Ic continuous is like 10A.

No inductors or resistors between the flash and capacitor. A cap that size is more than resistive enough to require no additional help.

This approach definitely turns off the flashtube: after sitting a while, the camera has to recharge the cap before you can take a flash photograph. Once it's charged, you can take lots of flashes with little delay. And that's while it does its double flash thing. Pretty neat.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

On a sunny day (Sat, 30 Jan 2010 14:19:01 -0600) it happened "Tim Williams" wrote in :

Do you put it back together :-)?? Maybe that cap is inductive too? may be worth measuring it, if it is a foil type electrolytic sometimes those become inductive if the foil does not make good contact over the edges...

I would not dare to take my Canon apart, it is a far too nice camera.

Reply to
Jan Panteltje

Ha! Tried...

Well, this one was making shit like this,

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which I later learned means the CCD assembly is faulty (corrosion, tin whiskers?). My second S1 did the same thing, Canon fixed it at no cost to me.

A friend says he's fixed a number of cameras, but refuses Canons because they are impossible to put back together. Hey, I tried...

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

k

Only 1 and I think that is enough. :) The "data book" had about 3 devices in it and had a tank on the cover. The name of the company was something like Powertek or powerteck IIRC the price tag had more digits in it than I cared to think about.

and

I've already seen that. Doc Edgerton built it in WW-2. The flash had a refector about 3 feet across and the flash tube was about the size of a couple of human fists put together. The box that made it go was a couple of feet on a side.

It was developed to take photos from the air at night.

like

...

GTOs don't like really fast di/dt. They don't spread the conduction state over the whole device unless there is some current flowing. It takes a while for the whole device to get turn on.

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rom

und

han

I wasn't figuring on a 1206 NPO.

Reply to
MooseFET

On a sunny day (Sat, 30 Jan 2010 18:14:46 -0600) it happened "Tim Williams" wrote in :

Hey Tim, if you hang that in some exposition, you just need to know the right persosn, chances are it sells as modern art for half a million :-)

Reply to
Jan Panteltje

I just thought of another interesting way to do it:

The idea of using a second SCR to short the terminals of the tube is good except that it requires the the SCR take a huge current spike to discharge the storage capacitor. Another device that can take a big current spike is another tube.

----/\/\--------------- ! ---+-------+-----!!-----+- ! ! ! =3D=3D=3D [Tube1] [Tube2] ! ! ! ---+-------+--------------

Tube1 is the working tube.

Tube2 is a second tube that is hidden.

The capacitor feeding Tube2 is so that Tube2 will have a slightly higher voltage on it than Tube1. This voltage difference is equal to the struck voltage of Tube2. When Tube2 fires it forces the voltage on Tube1 to near zero.

Reply to
MooseFET

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Steve

Reply to
osr

You can also use a smaller tube to "shunt" the main tube, but you must shield the "shunt" tube from the ignite pulse and the UV light of the main flash.

They used to make a NE2 sized xenon tube as a shunt, but now you could use a 1" tube froma disposable camera, or a triggered spark gap.

Steve

Reply to
osr

Or you could have multiple capacitors charged up. Discharge no 1 followed by no 2 ( if no 1 did not provide enough light ). Followed by no 3 if no 1 and no 2 did not provide enough light.

This would give a slightly longer time, but surely could discharge three or four caps in less than 2 ms.

Dan

Reply to
dcaster

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