Finding alternate to obsolete MOSFET VP0120N5

Discussion in 'The Projects Forum' started by Michael Oswald, Mar 17, 2015.

  1. Michael Oswald

    Thread Starter New Member

    Mar 17, 2015
    Hi everyone. I am a mechanical engineer with a very basic understanding of electronics. The company I work for is small, and we lost our EE a few months ago so all of this falls to me. I was working with some old test equipment (at least 15 years old) this morning and it broke. In a nutshell, the box supplies a variable voltage to our RF circuitry for testing. There is no schematic for the equipment, so after a few hours of tracing out the various connections (it's all built on a breadboard, wires everywhere) I've isolated it to a p-channel MOSFET, VP0120N5. Of course these are obsolete and not available anywhere. So I need to find an alternative.

    After googling and reading through other forum posts I think I should be looking at these parameters (I'll include the values for the obsolete part in parenthesis):
    Drain-Source Breakdown Voltage (200V)
    Continuous Drain Current (-.425A)
    Resistance Drain-Source (ON) (15 or 25 ohms, depending on the testing condition)
    and of course a p-channel with the same TO-220 package

    I'm guessing that for the voltage and current specs I should be looking for a part with at LEAST the above values. But I'm not sure about the resistance. And power dissipation (15W) seems to me to be pretty important too, although maybe that gets worked out between the continuous drain current and drain-source resistance.

    I can't seem to find anything close on the Mouser website (seems a tradeoff between current and resistance specs), but maybe I'm just looking in the wrong category. Any suggestions would be appreciated. Thanks so much.
  2. Papabravo


    Feb 24, 2006
    I'm an electrical engineer with a very basic understanding of mechanics. Do you really want me screwing around with drawings and specifications to troubleshoot the locks on the Panama Canal. I didn't think so. Hire a professional, you and your company will save money and time in the long run.
  3. tjohnson

    Active Member

    Dec 23, 2014
    I just did a Google search for "buy MOSFET VP0120N5", and actually there still are some places that appear to sell them online:
    It probably would be preferable to replace it with a different component, but I thought I'd mention it.

    Disclaimer: I'm not an electronics expert (I don't even know what MOSFET stands for). I'm just trying to help.
    EDIT: Metal-Oxide-Semiconductor Field-Effect Transistor (I looked it up)
    Last edited: Mar 17, 2015
  4. Marcus2012


    Feb 22, 2015
    If you aim to replace it with a modern analogue I would suggest getting one with values for breakdown voltage and drain current that slightly exceed your requirements. You won't find a P-channel with that Id and that high a Rds (on) anymore so I think that's ok just get a lower Rds value one that has matching current ratings. But do try and get one that has rise/fall times (and turn on/off delay etc.) and gate capacitances that are similar (as this is the switching time characteristics), and try and match the Vgs threshold voltage too. I think that should be ok but without a schematic for the device and understanding of this particular MOSFETs function its a risk to replace anything.
  5. Michael Oswald

    Thread Starter New Member

    Mar 17, 2015
    Thanks so much, I'll check those sites out. I had originally been searching for the n-channel version as well (VN0120N5) and could only find stock in China, so was assuming the p-channel would be the same. I want to update the parts, but this would give me some breathing room until I have more time.
  6. Michael Oswald

    Thread Starter New Member

    Mar 17, 2015
    Thanks Marcus, I appreciate the help. I'll keep those parameters in mind when I'm looking for a more-readily-available replacement.
  7. DickCappels


    Aug 21, 2008
    The Fairchild Semiconductor FQU5P20TU looks promising. It is at Mouser at less than US$1 plus shipping. It is probably available elsewhere. No guarantees since we don't know the details of the application.
  8. uwed


    Mar 16, 2015
  9. Michael Oswald

    Thread Starter New Member

    Mar 17, 2015
    Thanks so much for everyone's help - it really gets me out of a jam. I really appreciate the suggestions on alternates.