Electronics > Projects, Designs, and Technical Stuff

a solid-state kilovolt (de)multiplexer?

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ledtester:
I was watching this Electroboom video:

https://youtu.be/gqng2MPClO8?t=8m25s

and I was wondering how to do implement it without the motor (skip to 8:25 to jump right to the setup.)

Someone in the comments suggested that a car distributor might work. Is there a solid-state solution for this kind of high-voltage demultiplexing?

T3sl4co1l:
That's probably at the point you'd want to use x-ray or beam switched semiconductors.  Take a lump of intrinsic semi, blast it with energy, free up charge carriers, profit.  Just a photocell, but using the bulk.  Optical light doesn't have enough penetration depth, it's more of a surface thing.  Penetrating radiation is needed, such as x-rays or beta rays.  Which are obviously not the cheapest thing to come by, as you need a vacuum tube and high voltage.

A reminder what you're asking for.  When you say "this kind of" thing, you're talking about quite high voltages (10s kV), with peak currents of hundreds or even thousands of amperes -- capacitive discharge, fast rise times (air ionization occurs in a few nanoseconds).  To be able to mux that, you need some pretty nice switches.

If you were just distributing a little current here and there, you'd still have a problem switching it; transistors are driven with a few volts, which has to be isolated to fly on top of thousands.  You could do the same thing over again, just using optical light -- photocells or photodiodes, activating a surface layer so the conductivity kinda sucks but that doesn't matter for ~uA.  Photodiodes of course have to be used back-to-back; and their gain sucks but again, for ~uA that's fine.  (Photodiodes also having the downside of generating photovoltage, which should cancel out in a back-to-back arrangement, which can be trimmed by adjusting individual illumination.)

The way power companies do it (switching many megawatts) is with big stacks of transistors (usually thyristors, since the gain is much higher, the frequency is low, and the load is AC), and isolated drivers, which are either self (parasite) powered, solar powered, or transformer coupled.  Transformers that can isolate hundreds of kV don't perform well, so the use of solar cells really is pretty attractive, despite the poor efficiency!  (There are also direct optical triggered SCRs, which I'm not sure how common they are, but it's a thing.)

Tim

KT88:
If you have deeeeep pockets: http://www.behlke.com/

TheMG:
If you want solid state the easiest and cheapest way to do this is going to be individually controlled high voltage sources (one high voltage transformer dedicated to each output). Switching such high voltages (and peak currents) by solid state components is no trivial (or cheap) task.

jbb:
Direct optically triggered SCRs are cool. Sadly, I heard from the semiconductor team at my last job that you had to make so many silicon compromises so the optical trigger works that the electrical performance isn’t very good.

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