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Marx generator power supply protection
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MRMILSTAR:
I built a 20-stage Marx generator. The power supply is a flyback transformer driven by a ZVS driver. The ZVS driver is powered by two 12-volt batteries in series for a total of 24 volts. The Marx generator works as expected with 6 inch sparks, or greater if I want to push it. The problem I am having is how to protect the HV power supply, in particular the ZVS driver. The ZVS driver is one of those Chinese $10 units which uses a standard circuit. The problem I have had is that some of the HV discharge kicks back into the flyback secondary. This then appears to induce a voltage into the flyback primary (center-tapped coil with dual 4-turn coils). The induced voltage then kicks back into the MOSFETs of the ZVS driver. Sometimes this voltage exceeds the source-to-drain voltage rating (250 volts) of the MOSFETs and blows them out.

One idea that I had was to connect varistors across the ZVS driver output. One varistor across one 4-turn coil of the flyback primary. Another varistor across the other 4-turn coil of the flyback primary. The 3rd varistor would then connect across the outer turns of the two coils. I know that varistors have a limited lifetime but the Marx generator only fires about every 3 seconds so I think the varistors would last a reasonable amount of time. They are inexpensive and easy to change.

If this seems like a viable approach, what peak voltage rating for the varistors should I use? If this is not a viable idea, does anyone have any other method for protecting the HV power supply?
T3sl4co1l:
What transistors does it use?

Tim
MRMILSTAR:

--- Quote from: T3sl4co1l on October 25, 2018, 04:33:27 am ---What transistors does it use?

Tim

--- End quote ---

IRFP250 MOSFETs
T3sl4co1l:
I would guess, use a ~140V TVS or ~100V MOV, tied as close as possible (shortest wiring distance) to source-drain, and also a 15V TVS from source to gate.

Tim
coppercone2:
I have a HV pulse circuit thats setup to be triggered with IR that I bought from some national defense lab or something. It discharges a special tube through a transformer, but I noticed something strange about it, the HV supply was connected to the rest of the circuit by a very large choke, I think like 5Henry. I could not figure out for sure what it was, but it isolated the capacitor from the solid state DC supply. I think it might be protection. The supply is too weak to to require current limiting to the capacitor ESR.
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