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Substituting NFET for PFETS?

Discussion in 'Electronic Basics' started by Guest, Aug 9, 2003.

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  1. Guest

    Guest Guest

    I'm wondering if someone could please help out a novice...

    I'm trying to build the following circuit, but my local supplier, RadShack,
    only carries N-Channel FETS, not P-Channel as specified by the schematic.
    Can someone recommend a simple solution with NFETS, or perhaps an
    alternative altogether.

    Here is the circuit: http://www.animalrushhour.com/brad/pfetcircuit.gif

    Which is actually part of this document regarding driving higher current
    LEDS with the MAX7219:
    http://www.maxim-ic.com/appnotes.cfm/appnote_number/1196

    Thanks!

    -Brad
     
  2. Ban

    Ban Guest

    Brad, you can also save a lot of money taking these bipolar PNP transistors
    instead. They can switch around 100mA max.
    If the driver voltage is higher, you can insert a cascode stage similar to
    the drawing in the data sheet.


    Vdriver
    +--------+----------o
    | | less than 10V
    .-. |
    1k| | |
    | | |
    '-' |
    | |<
    +------| 2N3906
    | |\
    .-. |
    1.8k| | |
    | | anode digit drive
    '-'
    |
    o
    Dig0...Dig7



    Vdriver
    +--------+----------o
    | | more than 8V
    .-. |
    1k| | |
    | | |
    '-' E|
    | |<
    +------| 2N3906
    | B |\
    .-. |C
    | | |
    1k| | anode digit drive
    '-'
    |C
    |/
    +5V o------| 2N3904
    B |>
    E|
    .-.
    | |
    1k| |
    '-'
    |
    o------+
    Dig0...
    created by Andy´s ASCII-Circuit v1.22.310103 Beta www.tech-chat.de

    ciao Ban
     
  3. B. Woods

    B. Woods Guest

    That looks like the advice I was looking for. I'm pretty good with digital
    electronics, but analog still holds many mysteries for me.

    Thanks!
     
  4. Cyrus

    Cyrus Guest

    Use one of these for Q2.

    Radio shack P#
    900-5549 VP0300L Vds= -30V Id= 0.320 Amp TO-92 $.99
    900-5548 VP0300B Vds= -30V Id= 1.250 Amp TO-39 $6.59
    900-5194 IRF9510 Vds= -100V Id= 4.0 Amp TO-220
    $1.16

    You can order it from your local R/S or call 1 800 442 7221

    Good luck,
    Cyrus
    ( please reply to group )
     
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