1-2mA surge current limitter for megger. Need help!

[001]

Hi!

I'm going to make simple diy megger/ insulation tester
Like vintage analog: 2.5kV rectifier + galvanometer
But i see what modern meggers have safety current limiter about 1mA at zero load

Current limmiter is a basic thing
But
What is the adequate way to add it to hi voltage circuit?

[T3sl4co1l]

A big fat resistor helps a lot.

There isn't much else you can do, to limit current on microsecond time scales.  Even that is difficult, because space itself holds a lot of charge at those voltages.

If it's just for steady state current limiting, anything can do: a resistor, a current limit circuit, a controlled current power source, etc.

Tim

[001]

A big fat resistor helps a lot.

No matter

Output impedance is limited by measuring purposes 

[oldway]

You could use a very high voltage Mosfet as  IXTA02N450HV made by Ixys (Vdss Max = 4500V) as current limiter.
http://www.pankajelectronics.com/semiconductors/mosfets/n-channel-standard-power-mosfets/2500v-to-4500v-very-high-voltage-power-mosfets/ixta02n450hv?zenid=aldghoh59s4p8rc1b1h8huuqg5

[001]

Interesting mosfet
Who use this circuit? Is it a part of similar project, isnt it?

[oldway]

Interesting mosfet
Who use this circuit? I don't know, I did not copied it from Internet, it is such a simple schematic.  Is it a part of similar project, isnt it? I don't know....So simple circuit....may be...

[T3sl4co1l]

It's just a "ring of two" current source circuit, made two-terminal by the bias resistor (which unfortunately spoils the CCS characteristic).

If they make depletion MOSFETs with voltages that high, that would be even better -- self biasing, no need for the large value resistor.

You can also stack lower voltage DMOS CCSs; the voltage will not be shared equally, with some being saturated, some avalanching (a TVS would be good, to improve ratings), and about one doing the actual regulation, but that's alright when high accuracy is not required, and when the power ratings of each transistor are designed safely.

Tim