Interupting xenon flash current ?

It's probably laminated steel, with a lot of winding capacitance, too slow for this measurement; but you could test it.

John

flash duration.

The EG&G Microflash seems to be out of production, but

Thanks, I see I have an electrode stabilized lamp (arc length / bore dia ~ 2, which should be good for short duration flashes), and a resonant discharge power supply.

Ain't he from Wisconsin? ;-)

Tim

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

Oh, something else comes to mind: xenon-filled thyratrons are in the microsecond range ionization time, about 1ms deionization. These devices are at lower pressure than flash tubes, giving a diffuse blue to white glow discharge rather than an arc. Probably, a flash tube is somewhat faster, due to the higher pressure bringing the plasma bric-a-brack together faster. I don't know what cool-down time is, but if you feel adventurous, you could calculate it from the black-body radiation formula and an assumption of peak temperature, mass of the plasma and its heat capacity.

Tim

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

Unfortunately mine has an e/r of about 8, not so good for short flashes.

Mike

When truth is absent politics will fill the gap.

Mike snipped-for-privacy@comcast.net posted to sci.electronics.design:

That is not going to work. You need a much bigger (or lower u(r)) core. Core saturation will trash everything.

John Larkin snipped-for-privacy@highNOTlandTHIStechnologyPART.com posted to sci.electronics.design:

OK some foolishly did. Probably to avoid a patent issue. Oh well, all the original ones are expired now.

GregS snipped-for-privacy@zekfrivolous.com posted to sci.electronics.design:

Was that a 5600?

John Larkin snipped-for-privacy@highNOTlandTHIStechnologyPART.com posted to sci.electronics.design:

Guestimate about 2 to 3 percent.

I would have to look at it.

greg

That inductor is sometimes used, mainly to shape the current pulse to reduce peak current and make the pulse closer to a square (more constant in current) than it would be without the inductor. They do that in laser pump strobes and elsewhere that stress on the flashlamp is greater.

I have picked into plenty of photographic flashes, including a couple larger ones, and I never saw that inductor being used there.

DISCLAIMER - I only dissected photographic flashes without means to adjust the flash intensity.

- Don Klipstein ( snipped-for-privacy@misty.com)

I have used photodiodes and oscilloscopes on camera flashes, and found flash duration to be more in the 1 millisecond ballpark. Sometimes a few milliseconds. Some very large ones I suspect to get into the 10 millisecond ballpark; I have yet to do that measurement.

- Don Klipstein ( snipped-for-privacy@misty.com)

GregS snipped-for-privacy@zekfrivolous.com posted to sci.electronics.design:

If (when) you do please post back here. I think i would like to have one. I am not comfortable withe Eprey.

Not that I looked at the datasheet, but a pulse with a peak of 60 amps and decaying exponentially with a 70 microsecond time constant has a charge of only 5.6 millicoulombs, doesn't it?

Is not energy stored in a capacitor half the charge times the voltage?

In my experience, most small to smallish medium photoflash capacitors are rated 330 volts. 1/2 times .0056 times 330 is is about .92 joule. If I should have used 80 amps rather than 60, then the energy is about

That sounds like an awfully small photoflash to me. I have seen about

- Don Klipstein ( snipped-for-privacy@misty.com)

In those "disposable" cameras, the capacitor is 110 to 160 microfarads and usually charges to about 300 volts or slightly more. In photoflash units better than those, the capacitor is even larger.

I have measured the voltage across the flashtube exceeding 250 volts at the beginning of the main somewhat-exponential decay of capacitor voltage when the flashtube starts discharging the capacitor.

- Don Klipstein ( snipped-for-privacy@misty.com)

I think 10 or even 20 us range should be just fine! Flash duration is usually in the 1 millisecond ballpark! - Don Klipstein ( snipped-for-privacy@misty.com)

It appears to me that this would be around 50-100 microseconds in usual smaller photoflash tubes.

I have made a xenon strobe with entire flash duration not much over 50 microseconds. Then again, I had the xenon plasma running hotter than usual for a photoflash in that one.

- Don Klipstein ( snipped-for-privacy@misty.com)

I've seen exactly one so far. Was a stack of copper turns, bank wound air core about 24AWG. In series between the cap and tube.

Nothing to do with the SCR, which discharges a film cap into the trigger transformer.

Tim

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

I mostly find something like 40 lumens per watt overall luminous efficacy.

In a really good case, 75-80% of the energy going intio the flashlamp becomes radiation. Most of this looks like blackbody radiation, but some goes into a cluster of major near-infrared lines around 820-1,000 nm. The percentage going into those infrared lines is greater when plasma temperature is lower, the flashtube is narrower and the xenon pressure is lower.

Maximum luminous efficacy of a blackbody is about 95 lumens per watt, at about 6600 Kelvin. Take 75-80% of that and maybe less with lower energy strobes, take a bit to some off for those infrared lines, take a little more off for the plasma temperature being other than 6600 K at least most of the duration of the flash, take a little more off for losses in series resistance, and I think one would do well to get half that 95 lumen/watt figure.

I somewhat remember 40 or maybe 45 lumens/watt from an old catalog from one of EG&G's divisions. I do suspect that with enough work into this, one could get 50 or 60 - along with light that is on the bluish side and a more expensive and bulkier capacitor (or array thereof) and a bulky expensive low-resistance inductor to shape the current pulse, and only at a higher flash energy in a larger (and more expensive) flashtube.

- Don Klipstein ( snipped-for-privacy@misty.com)