Connect with us

MOSFET terminology

Discussion in 'General Electronics Discussion' started by twiglet123, May 17, 2013.

Scroll to continue with content
  1. twiglet123


    Dec 30, 2012
    Hello all, I'm after buying a bunch of MOSFETs to run a few relays that i'm about to buy from rapid online.

    I'm controlling a fairly powerful motor from an mbed micro-controller that can output 3.3v and the solenoids I'm planning to use take 5v to operate.

    These ones here..

    Any recommendations for good cheap MOSFETs that will allow the desired voltage 5v to pass when I stuff 3.3v in at the gate?

    I'm looking at these ones at the moment..

    However I haven't a clue about any of the MOSFET terminology and haven't had much luck googling for results (VDS, RDS, ID cont and IDM mean nothing to me!).

    If anyone could provide a link to a good human friendly glossary of terms and make sure i'm buying the right thing i'd appreciate the help

    All the best
  2. BobK


    Jan 5, 2010
    I would not use a MOSFET in that application, and certainly not an P channel one. I would use an NPN bipolar transistor.

    The reason I would not use a MOSFET is because even the so called logic level ones typically require more than 3.3V on the gate.

    The reason I would not use a p-channel MOSFET is because when the gate is driven by a 3.3V micro and the source is at 5V this gives you either -1.7 or -5V on the gate, relative to the source. If the -5V would turn it on fully the -1.7 would likely turn it on partially.

    Also, why does it require a bunch of MOSFETs to run a few relays? I would have though that a few would do :)

    Last edited: May 17, 2013
  3. twiglet123


    Dec 30, 2012
    you thinking something like a 2N3904 or 2N2222A transistor?
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    As long as the relay current is well within their Ic ratings, yes.

    Remember to place a diode across the relay to absorb transients as the relay switches off (the diode has the cathode at the +ve end of the relay coil so it doesn't conduct while the relay is on. A 1N4001 is typically fine for this)
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day