Electronic – Using a depletion mode mosfet as a current limiting device

current-limitingmosfettransistors

I have recently discovered the exciting world of depletion mode mosfets. Curiously, even in this document, I found nowhere that a depletion mode mosfet could be used as a current limiting/inrush current limiting device.
But this is strange, because what prevent us to use them like this:

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or like this

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(with a suitable heat sink of course) ?

To put flesh on bones, I have built a 800V, 10-20 mA PSU. I have a IXTY01N100D depletion mosfet, with 1000V breakdown voltage and 400mA current. It is not so easy to build a conventional inrush current limiter at this voltage. I wonder if I can use this transistor to limit the inrush current in the filtering output cap.

Best Answer

It should work. It's a common use for depletion FEts and several examples in the document you linked to use them as current sources.

Respect the Safe Operating Area though:

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You can also make an AC current limiter with two depletion FETs:

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