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Registered Member #4034
Joined: Thu Jul 28 2011, 10:41PM
Location: somewhere in the Southern hemisphere
Posts: 138
I was wondering if you could build a marx generator with a couple of these type of devices? I've seen some rated at 400V trigger. Could you even use some kind of semiconducter?
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
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Posts: 635
Marx Generators are typically employed because the voltage and pulsed power are too high for typical solid state topologies. Not sure what kind of power levels you're thinking about, but you may want to consider a pulse transformer or something like that.
That being said, there are usually ways of replacing spark gaps with semiconductors. The complexity goes way up, though. I'm thinking you'll have to use MOSFETs for both speed and avalanching capabilities, because the last one to fire will have darn near the full voltage across it before turning fully on. Unfortunately MOSFETs aren't great for high peak power. You may go through a lot of trouble before realizing that a spark gap is probably your best bet.
As for the things you linked, I think it can be made to work as long as you make sure not to exceed its power rating. I hope you'll post the results here if you choose to pursue this experiment.
EDIT: Just noticed it is rated for 500Hz. That kind of frequency response is not going to give you the rise time needed for a Marx Generator. The problem with enclosed spark gaps is that they cannot be quenched effectively (i.e. by moving air). That will make it slow. Might be best to pass on this.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837
Sure you could use those kinds of spark gaps, but you lose the bonus of UV ionization making neighbouring spark gaps break down faster ... which I think is what gives spark gaps Marx's their fast rise time.
Solid state switches have all been used to build Marx generators with. Thyristors are probably easiest, since you can simply use GDTs with the primary simply being a HV cable straight through a toroid and a couple of secondary windings. They can't stand very fast dI/dt at turn on though.
MOSFETs and IGBTs require more complex gate drives ... a fast GDT with low turn count won't be able to sustain a long pulse (not a problem for the Thyristor, since it only needs a short pulse).
Avalanche transistors have also been used for Marx, but rated avalanche transistors are expensive and abusing normal transistors for it can be tricky.
More exotic stuff like Dynistors are even better suited, but almost impossible to find and/or expensive.
Registered Member #4034
Joined: Thu Jul 28 2011, 10:41PM
Location: somewhere in the Southern hemisphere
Posts: 138
hmm that last one gives me an idea what if you made a triggered spark gap for the first spark gap (forget the low voltage) and used it to power a washer laucher or something. you'd get extremely fast pulses with good rise times correct?
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Low voltage marx?
