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Powering a CO2 laser

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Dosinski

Sun Jun 19 2011, 10:29PM

Registered Member #2680 Joined: Wed Feb 10 2010, 09:23PM
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Posts: 45

I'm building a power supply for a 40W CO2 laser and i was wondering what's the best way of going about it. I'm thinking of using a ZVS flyback driver instead of a NST. The laser tube i have has a triggering voltage of 22kV and an operating voltage of 15KV. And i am wondering how crucial that triggering voltage is :/ Will the laser not start if i don't provide that 22kV jolt?

Dr. ISOTOP

Sun Jun 19 2011, 11:18PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

At your requisite power levels, you can probably use a hard-switched a ferrite transformer with an H-bridge, which is a lot more controllable than a Mazilli driver (just turn the pot to change the duty cycle and hence the output current; you can even regulate it).
The trigger pulse is pretty important. It can be generated with a small pulse transformer.

Pieznice29

Wed Jul 13 2011, 10:50PM

Registered Member #3918 Joined: Sun May 29 2011, 08:42PM
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Posts: 34

For my 40W CO2 I just used a ZVS driver with a fairly large TV's flyback transformer running at 24v with a 4+4 turn primary, the tube starts up just fine without any external trigger. It even starts on 12v but doesn't lase. It took many hours of playing with power inductor and tank capacitor values to get it to drive the tube with a decent current though.
I have been able to get up to about 15ma of current through the tube, which isn't quite the full 40W but it far more than what I use the tube for. I've got many hours of usage out of my hommade power supply and it doesn't seem to be doing damage to the transformer even with running at power levels it was never designed for.

ZVS driver with flyback is probably the simplest method for powering your laser, but im not sure how well it would work if you needed to switch the laser on and off pretty quickly. (e.g. in a CNC laser cutter application)

Best of luck with your laser adventures (:

Dosinski

Fri Aug 26 2011, 08:09PM

Registered Member #2680 Joined: Wed Feb 10 2010, 09:23PM
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Posts: 45

hv-friekie and I tried two different ways of powering the laser. First, using paralleled flybacks powered by one driver. The output was extremely weak trying to do this. It would barely burn wood. Also, doing this created voltage spikes which destroyed the mosfets. The second method we tried was using a rectified NST 15kV 60mA. The neon sign transformer was able to ignite the laser tube on its own.
Here are a few pictures:
Dscn0784d

Proud Mary

Fri Aug 26 2011, 10:29PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Coo, that laser looks good fun!

I have found a very quick and simple one-shot trigger pulse generator can be made by charging a good robust capacitor of 100nF - 470nF to 300V, and then discharging it through the primary of a car ignition coil. I have used a Russian spring-loaded one-shot electromechanical relay/contactor to complete the circuit, but any other type of fast contactor or electronic switch will do if it can handle the inrush current. I can't see any reason why a bit of switch bounce would seriously affect the HV output trigger pulse in a way that would stop it from firing the laser.

If you are able to measure L and R of the ignition coil primary, you can calculate its time constant. If you have a choice, a coil with a shorter primary time constant will be best for a pulse generator using an ignition coil (i.e. because of dV/dt operation)

hv-friekie

Sat Aug 27 2011, 03:46PM

Registered Member #2273 Joined: Thu Aug 06 2009, 07:02PM
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Posts: 37

Thank you

So, you described a way to operate the laser tube on pulse mode?

Or what function is the ignition coil supposed to have?

Proud Mary

Sat Aug 27 2011, 04:25PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

hv-friekie wrote ...

Thank you

So, you described a way to operate the laser tube on pulse mode?

Or what function is the ignition coil supposed to have?

To supply the initial 22 kV trigger pulse - but of course you might design a single circuit which supplied 22 kV at no load, and then dropped to the 15 kV working voltage under load as tube conduction arrives at equilibrium.

For example, if you had only the use of 15 kV NST, you might find the separate simple 22 kV HV trigger pulse generator helpful.

I have used the one-shot trigger-pulse generator I describe for firing three-electrode trigatron-type spark gaps.

hv-friekie

Sat Aug 27 2011, 05:32PM

Registered Member #2273 Joined: Thu Aug 06 2009, 07:02PM
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Posts: 37

oh, alright. Now i understand what you mean.

But the tube ignites surprisingly good, we didn't need any external trigger voltage. Seems like the no-ballast voltage of the NST is high enough to initiate the discharge.

Proud Mary

Sat Aug 27 2011, 05:47PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

hv-friekie wrote ...

oh, alright. Now i understand what you mean.

But the tube ignites surprisingly good, we didn't need any external trigger voltage. Seems like the no-ballast voltage of the NST is high enough to initiate the discharge.

My reply was in response to Dosinksi's original post - I didn't understand that the situation had changed since then.

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