PWM drive via mosfet - what does a series gate resistor do?

Discussion in 'General Electronics Chat' started by peskywinnets, Jun 7, 2013.

  1. peskywinnets

    Thread Starter Active Member

    Jan 19, 2009
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  2. peskywinnets

    Thread Starter Active Member

    Jan 19, 2009
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  3. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    A gate resistor separates a driver circuit (microcontroller) from MOSFET's parasitic capacitance and inductance. These parasitic capacitances and inductances for a resonant tank circuit, which causes oscillation or ringing.
     
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  4. cabraham

    Member

    Oct 29, 2011
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    I always use gate resistors, but typically 1.0 to 10 ohms for high speed PWM, 10 to 100 ohms for low speed applications. The 150 ohm value is rather high for a PWM gate drive. How fast is the PWM in Hz? A 150 ohm resistor will result in a slow FET transition from on to off and vice-versa. If it is a very small FET w/ low gate charge, I suppose 150 ohms could work. Just curious.

    Claude
     
  5. peskywinnets

    Thread Starter Active Member

    Jan 19, 2009
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    Their PWM is running at 1khz ....but I've a circuit in mind that will be using 20khz (I need to run it above audio hearing range), hence the curiousity (also my PIC VCC will only be 2.5V, so I'm figuring I can get away with quite a low value series gate resistor?)
     
    Last edited: Jun 7, 2013
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    20k is rarely needed for motor controls. 6 or 7k is not normally audible. A motor makes a terrible tweeter.
     
  7. peskywinnets

    Thread Starter Active Member

    Jan 19, 2009
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    this is for leds in an audio cct, not motors....and even these jaded 50 yr old ears can still hear up to 13khz (younger ears upto 18khz)
     
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