Simplistic MosFET HV Shunt Regs

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Sorry if this was asked previously in this thread; Wondering if it is possible to use the SSHV2 to produce 600V regulated power. Start with approx 700V raw. Potentially with the use of IXTP08N100D2 within the cascode and a different MOSFET than the IRF840?

Some had done near 500V with higher rated components if I remember correctly. I would have increased the gate resistors in the Mosfets cascode to 1k each and hoped for the best regarding lanes clearances and turn on transients...
 
Some had done near 500V with higher rated components if I remember correctly. I would have increased the gate resistors in the Mosfets cascode to 1k each and hoped for the best regarding lanes clearances and turn on transients...

Thanks Salas, the amp that this will be employed in will have soft start, so not a problem with turn on transients.

Do you think the FQA11N90C Mosfet is a suitable replacement for the IRF840 if I get some PCBs made to support it? If not, what characteristics in the shunt Mosfet should I look for?
 
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It has almost twice the typical value input capacitance of an IRF840 and fortunately this does not seem to create more than 3 degrees loss of phase margin in simulation with an input capacitance comparable 900V IRFAF50 in this circuit. So it may work well, but that's only simulation.
 
I too am looking to do a 600v regulator, but am a little curious about the SOA of the PNP transistors (MJE350s in my case). Is it simply a matter of cascoding them and ensuring the base current is shared equally from the voltage referance divider? For example using 3 MJE350s in cascode keeping the individual VCE around 200v each? It seems to sim well.
 
Good deal. One more question regarding the ciss of the shunt FET. Would there be issues with stablility using a lower capacitance device? I am eyeballing the FQP3N80C, an 800v device with half the input capacitance and lower gfs than the IRF840. Would this require changing of the zobel network? Would it simply be plug and play? The regulator will be fitted to a CCS loaded parafeed amplifier, so there won't be any major load swings.
 
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Driver is shunt regulated with VR tubes. I greatly appreciate your input, and thank you for sharing such a seemingly wonderful circuit so openly. I've just got the last of the parts for my first dive into the SSHV2. Most of the work is done on my P2P board and it will be used in my 350V bench supply. I am a big fan of open source, believing knowledge is best used when it is shared freely. Again, thank you.