Transistor or FET selection Help Needed

Discussion in 'The Projects Forum' started by RodneyB, Jan 14, 2014.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    I am wanting to switch a 2 Amp 12 Volt load from a transistor or FET. I would if possible like to switch it directly from the output of a PIC12F675. Please can you advise what is the best way of doing this. I have looked at several diagrams online and not really sure which way to go.

    Many thanks

    Rodney
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    U can use a logic level MOSFET.
    Salvage a broken UPS. They got plenty of high current MOSFET's
     
  3. John P

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    Oct 14, 2008
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    A Darlington transistor would also work, but the FET would be more efficient. It must be a "logic level" type though, and if your processor is running on less than 5V, you need to be even more selective.
     
  4. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Its running on 3.5 Volts do you have a part number for a LOGIC FET so I can look at a data sheet
     
  5. R!f@@

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  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    What is the load?
    Do you need a high-side or low-side switch?
     
  7. John P

    AAC Fanatic!

    Oct 14, 2008
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    I went to the Mouser catalog for you, and looked through their power transistors and there are lots of them to choose from, but what seemed to be the cheapest in a TO-220 package was the BUK95150-55A from NXP Semiconductors, 41 cents in singles. You don't have to be fussy though, just look at a given component's graph of voltage drop or resistance versus current and gate voltage. Like figures 7 & 8 in this document:
    http://www.nxp.com/documents/data_sheet/BUK95150-55A.pdf
     
  8. wayneh

    Expert

    Sep 9, 2010
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    That would likely be my choice, simply because I have a few laying around and I'd have to go shop for a logic-level MOSFET.

    The base current of the darlington, for a 2A load, would not likely be a problem for the OP's PIC.

    You could also use a regular MOSFET if you use the PIC to sink a small amount of current through a resistor (and a diode?), to hold the MOSFET gate low until the PIC output goes open (or high?). That would then allow the MOSFET gate to go to 12V and turn fully on.
     
  9. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Thank you everyone for all the Help I used an IRLZ44n MOSFET my load is only 2 amps. So I don't even need a heat sink as the specs show no heat sink necessary to 6 Amps.
     
  10. John P

    AAC Fanatic!

    Oct 14, 2008
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    Sure, that should work fine, although the Mouser catalog lists it at $1.95. However, you're ahead of the game if you have a box of them on the shelf doing nothing, and you can find a use for one.
     
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