Interupting xenon flash current ?

[John Larkin]

Fairchild Semi has this nice app note on IGBT in series with the tube
and a 555 timer test circuit for the pulse width

http://www.fairchildsemi.com/an/AN/AN-9006.pdf

then there is this piece of marketing drivel from power electronics
magazine

http://powerelectronics.com/mag/407PET06.pdf

MIT thesis

http://via.mit.edu/documents/negrete_2004.pdf

enjoy,

I do xenon as part of my livelihood at the University.

Steve the strobemeister.

In a typical xenon strobe, roughly how much of the cap electrical
energy becomes light?

John

 

[John Larkin]

It seems that all of the IGBTs designed for strobe use are limited to
150 Apeak, suitable only for small on-camera type flash tubes under 20
Joules, and I see the apparently typical CY25BAH-8F flash IGBT is
rated for a 5000 flash lifetime.

I just hauled a big flash unit from a ~1970 copier breadboard in from
the barn to see how they did it. This flash was designed to fire
around 5 times per sec continuosly 24/7 for about a year at around 10
or 20 J per flash IIRC; it has a 5" long 1/2" dia tube in a fan cooled
lamp housing and a 19" rack mount power supply with a big
ferroresonant transformer and bridge rectifier charging a 4" x 4" x 7"
capacitor with inacessible labeling. The capacitor does not discharge
very much per flash. In series with the tube is a 0.1 ohm wirewound
power resistor with 27 turns of edge wound metal strip 1.25" dia 7"
long, I calculate about 4 uH. This resistor drops enough voltage to
quench the arc very quickly after it fires, but without any adjustment
posssible.

I might be able to fire it up and measure the flash current sometime.

Hey John, do you have a core material recommendation for that 100:1 CT
idea?

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


John

 

[John Larkin]

No, they go to 10kA and higher. My circuit went
to 1.5kA and 1.2kV = 1.8MW. Look for IGBT modules
made by Powerex, Mitsubishi, Eupec, ABB and others.

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

John

 

[Phil Hobbs]

Yes, I've seen units that used a second flashtube.

John

That was Egerton's original method.

Cheers,

Phil Hobbs

 

[John Larkin]

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

 

[Robert Latest]

In a typical xenon strobe, roughly how much of the cap electrical
energy becomes light?

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

robert

 

[Robert Latest]

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

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

 

[Mike]

35A --> 175mA in the winding. It's probably made with fine wire (around
28AWG).

Doh, That makes sense.

A 200 ohm resistor sounds absurdly high.

They provide a little chart that shows:

200ohm -> 1V/1A
2K -> 1V/100mA
20K -> 1V/10mA

What V.s is it rated for?

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

Tim

The maximum freq is specified at 100KHz.
Sounds too slow to be useful here anyway.
80mHy on the winding.

Mike

When truth is absent politics will fill the gap.

 

[Mike]

No, they go to 10kA and higher. My circuit went
to 1.5kA and 1.2kV = 1.8MW. Look for IGBT modules
made by Powerex, Mitsubishi, Eupec, ABB and others.

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


Mike

When truth is absent politics will fill the gap.

 

[Tim Williams]

Mike. Re: your sig, see Godel's theorem.

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

 

[Winfield]

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

Mike

When truth is absent politics will fill the gap.

eBay is your friend.

 

[Mike]

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


John

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.

 

[Jim Thompson]

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

And I have a krytron!

John

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

 

[Glen Walpert]

No, they go to 10kA and higher. My circuit went
to 1.5kA and 1.2kV = 1.8MW. Look for IGBT modules
made by Powerex, Mitsubishi, Eupec, ABB and others.

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.

 

[John Larkin]

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

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

John

 

[John Larkin]

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.

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

 

[Mike]

eBay is your friend.

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.

 

[John Larkin]

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?
Yup.



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.

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

 

[Jim Thompson]

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

John

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

...Jim Thompson

 

[Rich the Philosophizer]

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.

Truth and Reality are two different things:
http://www.godchannel.com/reality.html

Cheers!
Rich