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:

enter image description here

or like this

enter image description here

(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.

  • \$\begingroup\$ See figure 6, 8 and 9. \$\endgroup\$
    – Oskar Skog
    Dec 26, 2019 at 10:28
  • 1
    \$\begingroup\$ I vaguely remember this application was mentioned in the AoE vol 3. I don't have it at hand to lookup now though. But you can definitely use depletion-mode MOSFETs as current-limiting devices. \$\endgroup\$
    – anrieff
    Dec 26, 2019 at 10:28
  • \$\begingroup\$ Another thing about depletion-mode MOSFETs is that they can be used with V_GS > 0. See this IXYS App Note "Depletion-Mode Power MOSFETs and Applications" for more current source circuits with them: ixys.com/Documents/AppNotes/IXAN0063.pdf \$\endgroup\$
    – ErikR
    May 21, 2021 at 14:14

1 Answer 1


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:

enter image description here

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

enter image description here

  • 4
    \$\begingroup\$ Thank you for your answer, and for the ac current limiting circuit. Yes, it is well known that a depletion mosfet can be used as a current source, but it is not always immediate that 1+1 = 2, I mean, that a current source could be used as a current limiter. Even The Art of Electronics does not evoke depletion mosfets in the chapter related to current limiting. That is what I found strange. \$\endgroup\$
    – MikeTeX
    Dec 26, 2019 at 20:23

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.