PWM controller getting hot

Discussion in 'General Electronics Chat' started by K SRINIVASAN, Sep 30, 2008.

  1. K SRINIVASAN

    Thread Starter New Member

    Sep 30, 2008
    1
    0
    why mosfet was heating in dc motor pwm controller i am used 500w, 24v,dc motor, i have used belove circuit what is the problem please help me
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Greetings! And welcome to AAC!

    I've moved your post into its own thread, where it will draw more responses.

    Please refrain from "hijacking" existing threads with tangent or off-topic questions. You can create new threads for new questions using the "New Thread" button on the upper left of the page.

    Can you post up a schematic?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Let's see - 24V @ 500W, so about 20.83A. Let's call it 21A.

    What MOSFET are you using? And as Beenthere asked, a complete schematic would be most helpful in helping you.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    This would be a good time for you to familiarize yourself with the process of attaching a file.

    Here is a link to the FAQ section of the aac forum. In this section, you should be able to find instructions on how to attach a file to your post.

    hgmjr
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    I think all of the following have been covered in AAC : Too large gate resistor[Im using 390 Ω,],drive output too high Z,too low voltage,sink or source in sufficient to supply gate capacity,;operating frequency to high;heat sink so small. If you can, monitor the gate waveform,do'nt be surprised if you see triangles inseead of squares.
    I hate the small pins on 80 A FETs.
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    Another cause is shoot-through current, caused by the lack of dead time in switching the top and bottom elements in the sides of the H-bridge.
     
  7. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    If you have a large input resistor as Bernard mentioned, then the transition from off to on becomes considerably slow and the MOS spends a lot of time in the linear region due to the internal gate capacitance, thus it heats up.Also, take care of the gate-source resistor which discharges the gate not to be very large as to switch off the MOS quickly and minimize the punch-through current.
     
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