transistor/mosfet help???

Discussion in 'The Projects Forum' started by mhastie1234, Feb 22, 2012.

  1. mhastie1234

    Thread Starter New Member

    Feb 10, 2012
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    I am building an h bridge running a 12v 5amp motor. What are the equations for determining to proper transitor or mosfet to use. Just wanted to know the math behind choosing one vs the other. I have looked at this link http://www.mcmanis.com/chuck/robotics/projects/esc2/FET-power.html but i find it hard to follow. Could someone simplify it for me. I was thinking of using tip147/142. I would like to know how much current they can handle in free air. Thanks
     
    Last edited: Feb 22, 2012
  2. Audioguru

    New Member

    Dec 20, 2007
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    Each TIP147/TIP142 has a maximum saturation voltage loss of 2V at 5A. Then each one heats with 10W and will need a fairly large heatsink.
    The motor will get only 8V.

    The "typical" saturation voltage is only 0.9V for each one. Then the heating is less and the motor gets 10.2V.
     
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  3. mhastie1234

    Thread Starter New Member

    Feb 10, 2012
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    Thanks Audioguru. Could you point me in the right direction and tell me what to look for when choosing a transitor / mosfet
     
  4. dumle29

    Member

    Jun 26, 2011
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    ive just whent through this, and recived a lot of help from audioguru (thanks! :D)

    The link you reffered to is hard to follow, but its REALLY nice.

    It took me a weeken of reading it every day, to understand it completely.

    and if you can fiqure it out, you will never blow a mosfett due to overload (unless thats your intention :p)
     
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
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  6. mhastie1234

    Thread Starter New Member

    Feb 10, 2012
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    In the link that i provided. I don't understand where he got 11.3mOhms from. Should it not be 11.9mOhms in the last equation and how do you get 214.16=I2 from 2.42W=I2*11.3mOhms. I understand the rest of the calculations just not this part.
     
    Last edited: Feb 23, 2012
  7. mhastie1234

    Thread Starter New Member

    Feb 10, 2012
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    Can someone help me out?
     
  8. mhastie1234

    Thread Starter New Member

    Feb 10, 2012
    29
    2
    figured it out.
     
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