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Simple switching question

Discussion in 'Electronic Design' started by [email protected], May 22, 2008.

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  1. Guest

    Hello,

    I need to switch 5V at a variable load (Something between 100 and
    900mA).

    I only have 5V at my disposal, and the load must be run at 5V, that
    is, there can be no appreciable voltage drop across the switching
    device. (I guess a drop of less than 0.4V would be fine)

    I was thinking that I could use a transistor to do it, and I grabbed a
    couple of TIP31s. I read here: http://www.kpsec.freeuk.com/trancirc.htm
    that when saturated, the Vce would be zero, but the datasheet for the
    TIP31, and my own test shows that this is not the case.

    What's the best way to do this?

    Thanks,
    Dan
     
  2. Guest

    If I use a logic level JFET, the Vgs will be zero for any load within
    my range if I wire it like so:

    Gate: My microcontroller
    Drain: Load (Load then goes to 0V)
    Source: 5V

    Right?

    (Fast switching fortunately isn't a concern, so I should be OK with
    driving this from a microcontroller, correct?)
     
  3. Eeyore

    Eeyore Guest

    Why would you use a JFET ? You need a mosfet.

    Graham
     
  4. Jamie

    Jamie Guest

    You need a logic power FET ..


    http://webpages.charter.net/jamie_5"
     
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