Why are p-channel mosfets so much bigger than n-channel

Discussion in 'General Electronics Chat' started by shaqywacky, Jan 29, 2011.

  1. shaqywacky

    Thread Starter Active Member

    Apr 1, 2009
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    I've been looking into learning about CMOS and I was going to get this book. To be completely honest I really don't understand this very much, that is why I'm getting this book. But I think CMOS is using P and N-Channel MOSFETs together. So I was planning on buying some p and n-channel MOSFETs from a website so that I could try out the things that the book does. The problem is that while n-channel MOSFETs are the right size and cheap, the p-channel are big and will barely fit in a breadboard. I am wondering why this is?

    Normally I would just read about them and understand what is going on but I am also buying something from that website which I need very soon and I would like to buy them at the same time so that I don't have to pay shipping twice.

    This is what I was planning on buying:

    N-Channel: http://www.goldmine-elec-products.com/prodinfo.asp?number=A20384

    P-Channel: http://www.goldmine-elec-products.com/prodinfo.asp?number=A20399

    Do you think those two would work for just messing around and learning about CMOS or do I not understand something here that makes this question not make sense?

    Thanks guys.
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    2,536
    You are confusing case styles with size. You can get MOSFETs in any package style you want. The TO220 is for heat sinks and will handle a lot more power because it can dump waste heat much better.

    Having said that, pMOSFETs are not as efficient as nMOSFETs. This has to do with internal construction techniques, not the case.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    CMOS means Complementary Metal Oxide Semiconductor, period.

    FETs, CMOS, and MOSFETs are all related. There are depletion mode FETs and enhanced mode FETs. You are looking at enhancement mode MOSFETs.

    The MOSFETs you are considering are not complementary; by that I mean they do not have similar attributes for Rds(on), Vdss and gate charge.

    P-ch MOSFETs that have an N-ch complement have to have a much larger gate surface area, as in a P-ch MOSFET, it's the holes that have to flow rather than the electrons. Electrons flow much easier than holes. The gate, being much larger, has a charge requirement that is roughly 2.5 times as large as that for an equivalent N-ch MOSFET, which is why P-ch MOSFETs have fallen into disfavor.

    The complement to an IRF9510 P-ch MOSFET would be listed as an IRF510, which is an N-ch MOSFET.

    You have not said what you wish to drive the gates of these MOSFETs with. The 2N7000 requires a Vgs of 5v to turn on, but the IRF9510 requires a Vgs of -10v to be considered fully turned on (saturated).
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    The 'CMOS Cookbook' is mainly about logic gates, not mosfets. It is a very informative book though.
     
  5. shaqywacky

    Thread Starter Active Member

    Apr 1, 2009
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    Ok, Thanks for clearing that up. I think I'm going to try a more general intro to electronics book.
     
  6. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
    90
    The Art of Electronics by Horowitz and Hill is a good book that is written in an easy to understand manner. The paperback version is on eBay for a good price.
     
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