I'm faced with the following problem. I would like to send a current pulse of about one amp through tissue with a resistance of about 3000 ohm (so I need 3000 V obviously).
The pulse should be as short as possible (I'd say no longer than 10 µs). The shape of the pulse is not that important, but it should be reproducible and short and deliver about 30 mJ or more.
And the whole thing should be as cheap as possible.
So far I've collected the following ideas:
Building a mini Marx Generator:
Kind of like this http://www.electricstuff.co.uk/marxgen.htm
Maybe triggered by a relay.
As i understand it the unloading time decreases with the capacity, so two charged capacitors connected in series would halve the unloading time, so one could work with this (according to my estimates) but I'm not really sure about the reproducability and I have little experience in electronics anyway.
Another idea would be to use a flashlight used in photography, here I'm not sure if the pulse would be short enough. Or a high voltage switch.
I'd be grateful for any ideas thoughts and suggestions.
Best Answer
Your requirements are conflicting. You say 1 A at 3 kV for no longer than 10 µs, but then say you need about 30 mJ, which is 1 A at 3 kV for 10 µs. It seems there is very little wiggle room.
My first reaction is to use a car ignition coil. They can certainly put out 3 kV for short periods of time, and the total energy is nicely limited by what is stored in the magnetic field before the primary is shut off. If you really care most about delivered energy, then this will work well.
However, getting a square pulse at a controlled voltage and time will be more difficult. If you are willing to waste most of the energy, then a 3 kV clamp would work. You adjust the energy so that the time at the 3 kV clamp limit is the 10 µs you want. Possibly multiple ignition coils will need to be in parallel.