Interupting xenon flash current ?

High-mu ferrite toroid, vaguely 1" OD should work.

John

Yeah, but they're bigger than the average camera. Cost more, too.

John

That was Egerton's original method.

Cheers,

Phil Hobbs

I have his book, full of beautiful pictures of hummingbirds and stuff.

And I have a krytron!

John

More if it's a tantalum cap. Maybe with a bang and some smoke to boot.

robert

I oce practically inhaled a book on high-speed photography (bullets and stuff). They used simple air gaps as light source because Xenon flashes apparently last too long. I think when photographing a flying bullet with this method the bang from the flash will be louder than that of the gun.

robert

Doh, That makes sense.

They provide a little chart that shows:

Strange, There is no mention of a voltage rating at all.

The maximum freq is specified at 100KHz. Sounds too slow to be useful here anyway.

Mike

When truth is absent politics will fill the gap.

I was hoping for something that doesn't require government funding to purchase.

Mike

When truth is absent politics will fill the gap.

Indeed: If there is no absolute truth, then nothing can be known. Assume there is an absolute truth: then something can be known.

Sounds good to me. A far sight better than "there are no absolutes", which is a mockingly ironic statement.

Tim

-- Deep Fryer: A very philosophical monk. Website @

eBay is your friend.

From what Tim pointed out to me, If I want to measure a pulse up to 2KA at 1:100 I have to deal with a 20A secondary pulse. Even at 500A it would still be a 5A sec pulse. Do I have this right?

While rewiring this experiment I have connected 4-600uf/360V flash caps is series with equalizing resistors to reduce the capacitance and allow me to charge to a higher voltage. I want to shorten the rise time of the light pulse as much as I can. I think my next test will be 150uf charged to 550V. That's just little over 20J and down from the 37J pulse I had earlier, but still should be plenty bright. I want to see how quickly the light pulse reaches it's peak. I better find a pin photo diode to monitor that and try to deal with commutating the pulse later. Maybe unrealistic, but I'd like to see a light pulse peak in 1us, but certainly < 10us.

Mike

When truth is absent politics will fill the gap.

My wife worked for Edgerton while I was a student at M.I.T.

"Doc" used to have monthly steak fries in his lab, using an old-fashioned galvanized wash tub as the charcoal grill. And he'd play his guitar and sing ;-)

...Jim Thompson

Yes, they go much higher than 150 A, but they seem to list applications like power supplies, induction heating and welders on the data sheets, not zenon flash control. And more to the point, I have not yet found any of these big IGBTs that even have a single or low repitition pulse rating; the data sheets all seem to assume PWM use.

I am considering building a new power supply for my large tube to allow very short flashes (~1 uS) with controls suitable for high speed "equivalent time" photography with a low cost 30 FPS camera, where for instance each frame would image a mechanism 1 uS later in its repeating cycle. But I think some measurements are in order before selecting an IGBT for the job.

I don't think Doc and Fred would have got along.

John

You don't need an igbt, and they're slow anyhow. Just pick a capacitor size, and arrange the parasitics, to dump the energy in less than a microsecond.

I don't know how fast the xenon will quit making light after the current is gone.

The igbt's are needed in cameras where the scene is unknown and unmetered before the shot. A sensor integrates bounced-back light during the exposure and shuts off the flash when it's had enough. That's especially useful for real film with a slow mechanical shutter.

For "studio" setups, there are simpler ways to control exposure.

John

purchase.

Naa, The fools said I was crook and threw me off. Funny thing is I wasn't even selling anything. Trust me, don't try to talk to them either!

Anyway, Those really big IGBTs seem a little on the slow side to shut off the tube current down in the 1us range.

Mike

When truth is absent politics will fill the gap.

Yup.

series

higher

think

down from

how quickly

that and

to see

Oil or film caps have low esr, and some can be arranged for low esl. Keeping inductance down, in the caps and wiring, is important.

Anybody know the speed of the xenon itself?

I built a xenon/pmt lidar when I was a kid, but the light flashes were circa 10 usec, and the optics were terrible, so it didn't work very well.

John

Yep. It'd be too emotional for him ;-)

...Jim Thompson

Truth and Reality are two different things:

Cheers! Rich