Xenon flash tube SPICE model

I can't help too much. The physics of gas discharges requires at least two spatial and one time dimension of PDEs coupled to at least six-dim ODEs to apprehend well; if you don't include radiation transport and atomic interactions. (I spent a little time studying the math because of a small interest years ago, but not for Spice.)

A simplified version may use global rate equations, assuming spatially averaged densities for the charged particles, with neutral atoms and molecules. But it still needs to deal with excited and metastable states.

There is an intermediate text by Lieberman & Lichtenberg called "Principles of Plasma Discharges and Materials Processing." It does a good job treating the fundamentals of discharges, global models, collisions, and DC and RF discharges.

I usually look to Cern for questions like this, so that's where I started to lool. A quick google search specifying their site came up with this:

There is a LOT of information in there, including various circuits as well as curves you may be able to use. However, you will also find this comment, "Many electrical engineers have attempted to model the impedance of a lamp, called Ko, using standard circuit simulation packages such as PSpice. Unfortunately, one cannot accurately model the impedance of an arc plasma using a series or parallel combination of passive elements. This is because the plasma impedance is non-linear and changes with time for the case of a flashlamp." They then go into some detail on the non-linear nature and time-dependencies.

What mode do you plan in operating it? (Some methods, which improve life and keep the plasma streamer in the center and away from the surface of the tube, are quite different than others -- and the shape of the cathode is different, which impacts the model one might use.) Gas pressure is another factor. So is the dead volume, located behind the electrode tip. (I really don't know what a discarded photoflash unit uses, but the above PDF from Cern says that flash lamps vary from something like 700 to 2300 Torr.) And many other things that the above Cern link gets into.

I think the above link will get you by, though the plasma physics book will give you still more. It's intermediate -- not advanced -- so it's not as overwhelming as a plasma physicist would be.

Jon

look

Jon Kirwan wrote in news: snipped-for-privacy@4ax.com:

Thanks. A very nice document.

20Eg&G.pdf

Eww ick. And nothing specific to little photoflash units, or a mapping from data sheet parameters (assuming that any could be found) to real life.

Oh well. I guess that's why I have an oscilloscope.

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Found this old NE-2 model in my libraries. Might be scalable to a flash tube if you have data...

******************************************************************

• * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

• Small Neon Lamp Behavioral Model Copyright 2003 by snipped-for-privacy@ieee.org

• Vs: strike voltage (bi-directional)

• Ii: threshold current boundary between strike and hold voltage

• Ti: ionization time constant of gas

• Vh: hold (regulation) voltage within normal current range

• Rh: on resistance within normal current range

• Ia: transition current to the increasing resistance of abnormal glow

• * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

*.subckt NE-2 A1 A2 params: Vs=90 Ii=50u Ti=.5m Vh=50 Rh=1k Ia=3m *Varc A1 arc 0 ; current sense *Barc arc A2 I= sgn(V(arc,A2))*uramp(abs(V(arc,A2))-V(ref))/(Rh*V(abn)) *Carc arc A2 5p ; stray terminal capacitance *Bref 0 ref I= Vh+{Vs-Vh}/(1+V(ion)**2) Rpar=1 ; voltage transition *Cref ref 0 1n ; tiny capacitance here aids convergence *Bion 0 ion I= abs(I(Varc)) Rpar={1/Ii} ; measure of free ions *Cion ion 0 {Ti*Ii} ; gas ionization time constant *Babn 0 abn I= {Ia**2}+I(Varc)**2 Rpar={1/Ia**2} ; abnormal glow *Cabn abn 0 1p ; tiny capacitance here aids convergence *.ends NE-2

• * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

****************************************************************** .SUBCKT NE-2H A1 A2 PARAMS: Vs=130 Ii=50u Ti=1m Vh=80 Rh=1k Ia=4m Varc A1 arc 0 ; current sense Garc arc A2 VALUE = {sgn(V(arc,A2))*LIMIT((abs(V(arc,A2))-V(ref))/(Rh*V(abn)),0,1)} Carc arc A2 5p ; stray terminal capacitance Gref 0 ref VALUE = {Vh+(Vs-Vh)/(1+V(ion)**2)} ; Rpar=1 ; voltage transition Rparref 0 ref 1 ; Cref ref 0 1n ; tiny capacitance here aids convergence Gion 0 ion VALUE = {abs(I(Varc))} ; Rpar={1/Ii} ; measure of free ions Rpar 0 ion {1/Ii} Cion ion 0 {Ti*Ii} ; gas ionization time constant Gabn 0 abn VALUE = {Ia**2}+I(Varc)**2 ; Rpar={1/Ia**2} ; abnormal glow Rparabn 0 abn {1/Ia**2} Cabn abn 0 1p ; tiny capacitance here aids convergence .ENDS NE-2H ******************************************************************

Watch the wrap :-( ...Jim Thompson

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Closest thing I could quickly come up with. At least it has pretty graph pictures and even some crafted thinking.

The article includes some eight canonical driver circuits, at least. (Probably just ones you've seen many times before.)

In any case, if you do have fun with the oscilloscope and find anything interesting to say about it and can muster up the desire to write, I'd very much appreciate a post on the topic.

Jon

If its any help, the self breakdown voltage of your average 1" camera lamp is about 1200-1400 volts DC when I measured it. They usually leave 40-60 VDC left in the cap, and a typical discharge is 200 uS FHWM with no series inductor.

The No Spice thing in the EG&G data is true for big laser pumping lamps. I'm not so sure you can't model a 1" tube.

Edgerton's book," Electronic Flash, Strobe", had a pretty good simple emperical electrical model invented BDC, ie Before Digital Computing.

I'd need to pull the book out of storage. I may be able to do that tomorrow.

I was building huge arrays of strobes that had to double flash for a lab project. IGBTS were out of the budget, so I set the recharge up with RC combinations.

Usually I'd use the cheap disposable camera lamps with two banks of caps to get the speed up, one 10-20 uF discharge cap and a big bank of lytics for the recharge of the 10 uF cap. I'd use resistors between the two caps, having found that 10 to 20 ohms made sure the lamp went out once triggered ,and values less then 10 tended to enable formation of a long CW arc. The lamps will take the arc for about 4 seconds without damage. So if you can figure out the minimum sustaining current, I think your halfway there.

So a simple test would be to make sure your model extinguishes with certain known configuration of a RC circuit, and breaks down at 1200V.

Thats all the parameters I can remember, from 5 years ago. I hope that helps.

Steve