N mosfet burning in motor circuit!

Discussion in 'General Electronics Chat' started by charles19887725, Feb 26, 2013.

  1. charles19887725

    Thread Starter New Member

    Feb 26, 2013
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    0
    Please refer to my schematic, the circuit on the left working fine. On the right circuit when connecting all Mosfets, the bottom left N-channel Mosfet burns within 5 seconds, and the current reading from 12V power supply shoots to 10A! The motor speed immediately drop down when connecting to all Mosfets. I am guessing there is a short circuit from the top right mosfet to the bottom left mosfet? I know I am missing some important concepts could anyone help me on that, thanks!
     
    Last edited: Feb 26, 2013
  2. charles19887725

    Thread Starter New Member

    Feb 26, 2013
    3
    0
    Please refer to my schematic, the circuit on the left working fine. On the right circuit when connecting all Mosfets, the bottom left N-channel Mosfet burns within 5 seconds, and the current reading from 12V power supply shoots to 10A! The motor speed immediately drop down when connecting to all Mosfets. I am guessing there is a short circuit from the top right mosfet to the bottom left mosfet? I know I am missing some important concepts could anyone help me on that, thanks!
     
    Last edited: Feb 26, 2013
  3. timescope

    Member

    Dec 14, 2011
    298
    44
    The transistors are in the wrong places. Q3 and Q4 should be MTP3055, Q1 and Q2 IRFI9540. Also, connect the source leads of Q1 and Q3 together to one side of the motor and the source leads of Q2 and Q4 together to the other motor connection.
    Drain leads of Q3 and Q4 to +12v, drain of Q1 and Q2 to ground.
    Timescope
     
    Last edited: Feb 26, 2013
  4. charles19887725

    Thread Starter New Member

    Feb 26, 2013
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    0
    Thanks, now I have N-mos on top, P-mos on the bottom and when doing forward, I put PWM on forward pin, and put LOW on reverse pin, but the upper left mosfet doesn't turn on, which the gate voltage still pull to zero. Any suggestions? Thanks for the help!
     
  5. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    488
    How do you apply a positive Vgs voltage to the N-FET if it's in series with the load on it's source?

    The OPs circuit on the right has the FETs in the correct position, p-FET on top, n-FET below.

    @ OP: Are you sure you connected the p-FET correctly? The middle pin is the drain, it goes to the other FETs drain. The rightmost pin is the source , it goes to the 12V power supply.

    First of all, test your circuit with a different load, a lamp or something like this. Put a fuse according to your lamp rating in series with the power supply.
     
    timescope likes this.
  6. timescope

    Member

    Dec 14, 2011
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    This is not correct and will not work with mosfets. I was probably thinking bipolar transistors. The original circuit should work if connected correctly.

    Timescope
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
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    Sounds like shoot-through.

    Does the bottom right blow up when you reverse?
     
  8. timescope

    Member

    Dec 14, 2011
    298
    44
    Does the motor have a diode connected to it ? You should remove it.

    Timescope
     
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