Xenon flash tube

Re Rail gun: This from the thread about pain vs frequency. (well from that guys site... kinda a hoot.)

George H.

I never noticed any pain or aftereffects, once the afterimages faded, in a minute maybe. There is an initial bright, very sharp and spooky image, which transitions to a negative image, which then fades away.

A serious eye exam seems much more intense to me than this flash trick. A retina exam can be painful and leave me seeing purple for some minutes.

Not sure what good it is, but I saw a video where a guy fire of a tube with a piezo electric unit from a propane stove. Mikek

I made a math mistake... 1 mW * 0.1s = 0.1 mJ not 0.1 J.

George H.

That should work. You can also just ramp up the voltage until the tube fires on its own, at some kilovolts.

I bet an optical input, like a pulse from a blue or UV LED, could fire a flashtube too, probably at a pretty high voltage, close to the natural breakdown.

15 years ago I tried triggering one flashtube with the flash of another one. I never got it to work. I didn't try increasing the voltage.

Mikek

Good to know, thanks!

It needs UV illumination of the cathode. Either UV filtering in the tube(s), or poor focusing of the illumination onto the target electrode will defeat the effect. If the 'target' electrode is shaded, behind the reflector of the flash, that'd explain the difficulty.

Photothrystors are actually kind of interesting gadgets.

Electronic Goldmine Surplus sells common strobe parts at the right prices... You might start there.

You can trigger many ways, a pulse of HV on the external trigger electrode, or series injection triggering, using a transformer in series or a blocking diode to insert a trigger voltage. Even HV DC will trigger it.

Without the trigger pulse it takes 1000-1700 VDC from Anode to Cathode to break down one of the U shaped tubes.

This is good reading for the serious technophile:

About 15$ at Autozone gets you the classic car or tractor ignition coil, which works just fine as an external trigger.

Usually I use an MOC series opto-triac in a six pin package to push charge into the trigger SCR gate lead from a 0.1uf cap via a 100 ohm resistor. Charging current for the trigger cap comes via a large enough resistor that the SCR is starved below its holding current. I'm using half the Triac as an SCR.

If I'm not doing that, I use a 555 wired as an inverting driver and push the gate with 100 ohms off pin 3 of the 555.

If you can find a SGR20N40L or similar IGBT, this app-note lets you "Quench" the strobe by cutting off the current, and the same IGBT triggers the tube that cuts it off. That can be very useful for high speed photography, but I'd start with normal triggering.

Steve

Steve

Den onsdag den 9. september 2015 kl. 00.31.57 UTC+2 skrev snipped-for-privacy@gmail.com:

an ignition coil seems like major over kill, heres the innards of a disposble camera:

the trigger transformer is the yellow one

-Lasse

Ebay shows lots of trigger transformers, such as those at

Any of them should work with your flash tubes.

Cheers, Dave M

In my defense

In the US, Autozone or their competitors are literally everywhere. They usually stock the small coil. It IS overkill, but the three terminal one is fun for a hobbyist.

It will also fire the lamp off a mere AA cell, no need for 100-200V on the primary like a trigger transformer.

Steve

Photothyratrons?

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  \_(?)_

Den tirsdag den 8. september 2015 kl. 18.53.12 UTC+2 skrev DecadentLinuxUserNumeroUno:

depends on how you count

if the flash is shorter than ~160ms it is more than 30kW

-Lasse

On Wed, 9 Sep 2015 04:11:00 -0700 (PDT), Lasse Langwadt Christensen Gave us:

snip

Ever seen the quarter shrinker guy's page?

An ordinary NE2 neon bulb can be triggered with low levels of visible light. Failing neon night lights tend to only work in the daytime.

The flashtube is quartz, so will admit blue or near-UV light. It should work.

I sort of did that when I was starting my first xenon arc lamp.

By putting the spark gap in a silica tube, I got enough hard UV out of the spark to knock electrons off the electrodes of the xenon arc lamp, and it s tarted every time.

The subsequent copies used a commercial spark gap in hard glass tube, and n ot enough of the hard UV got through to do anything useful to the electrode s of the arc lamp.

You had to fire the starter repeatedly until a random electron in the arc l amp gap started the avalanche. Fine for starting a lamp that was supposed t o go on and stay on. Not great for flash lamp or the like.

My starter was a bit wimpy, and only kept up the 20kV starting voltage for a few microseconds - there was enough stored energy in the starter circuit to sustain the glow-to-arc transition once you got the initial discharge, b ut you did need that first electron to get everything going.

The Southampton Chemistry Department workshop tried a less wimpy starter, b ut it blew up my 24A at 20V constant current supply that kept the arc runni ng, which was a neat trick. I never did get to see what their scheme had bl own up - just heard about it a few years later.

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Bill Sloman, Sydney

Known as lascrs.

A xenon flash tube is more of an ignitron, really. I don't recall that there's a name for a light-stimulated one, so photoignitron would be descriptive, if nothing else.

Tim

--
Seven Transistor Labs 
Electrical Engineering Consultation 
Website: http://seventransistorlabs.com