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Registered Member #3447
Joined: Fri Nov 26 2010, 11:10PM
Location: North Jersey
Posts: 97
I've built a gas discharge (laser) current regulator roughly shown by the circuit below. It is driven by a linear power supply (up to 20kVdc) with only a 2uF filter capacitor.
As many of you know, my system resulted in oscillations in an as-yet-unidentified location, but it is most likely in the central current path itself (probably in the laser tube). I will be buying an oscilloscope soon to verify the frequency distribution of the oscillations. This is all in an effort to build an inductor to work with the filter capacitor forming an LC filter to damp those destructive oscillations.
My question is, can I just do this with several bobbins with say 24 AWG magnet wire, then potted in a PVC pipe or similar? An open core design is essential, I think, because of the dc component saturating any ferrous core.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
It's a shame that the author didn't specify just what he meant by 'high frequencies' in his belated correction.
You can start by putting a smallish capacitance in parallel with R in your diagram. Try 10nF to start with, and increase or decrease according to the results.
Registered Member #3447
Joined: Fri Nov 26 2010, 11:10PM
Location: North Jersey
Posts: 97
I'm sorry it's taken so long for me to get back to this project... Thank you, Proud Mary and others, for hanging in there with me. Money is always an object, and I've been saving up for that Rigol 100MHz oscilloscope.
The paper does actually specify the optimal frequency response thus, "The required bandwidth from the regulator is about 5kHz, since it has been observed that most feedback stabilization systems seem to give the best results at frequencies ranging from a few hundred Hz to a few kHz."
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
A little more elaborately than that :p Why can't it simply be grounded like in a normal cascode? With a high voltage MOSFET the control loop can pinch off and regulate the current without the grid resistor ... is it a safety measure?
Registered Member #311
Joined: Sun Mar 12 2006, 08:28PM
Location:
Posts: 253
Don't forget that many gas-discharge devices have a negative resistance characteristic, which will probably upset any attempt to regulate current without a suitable ballast resistor.
Registered Member #3447
Joined: Fri Nov 26 2010, 11:10PM
Location: North Jersey
Posts: 97
Hi Mike. I'm sure you noticed the high frequency current regulation circuit at the top. This replaces the ballast resistor with dynamic resistance at a selected current level proportional to Vc.
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Linear Power Supply and Active Current Regulation Across a Gas Discharge
