Gate resistence for MOSFET?

Discussion in 'The Projects Forum' started by vivek20055, Dec 11, 2012.

  1. vivek20055

    Thread Starter Member

    Nov 4, 2012
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    Hi,


    what is the value of gate resistance that must be used before MOSFET for switching operation?




    Thanks & regards,
    Vivek Alaparthi
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    One typically aims for zero ohms.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    Are you asking what resistor to use, connected to the gate?

    The purpose of the gate resistor is to limit the inrush current to some level that is safe for both the MOSFET and the device driving it. It may not be needed, and using a resistor will slow the transition time to charge and discharge the gate.

    Choosing the right resistor becomes increasingly important at higher frequencies.

    So, you'll get a better answer if you supply the experts here more details about what you are doing.
     
  4. vivek20055

    Thread Starter Member

    Nov 4, 2012
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    Hi,

    Thank you for your reply.I am designing a Induction heating system. I am using using the Mosfets for switching purpose and gate drivers(LM5112) for driving the MOSFETS.

    I am attaching the circuit diagram with this post and the PDF of LM5112 gate driver. In page number 9 you can find information regarding gate resistance.


    Could you please assist me with the value of gate resistance I need to use here.


    Thanks in advance ,
    Vivek Alaparthi
     
  5. wayneh

    Expert

    Sep 9, 2010
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    Don't. Not needed.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    You're showing a schematic, but not what kind of comparator/opamp you're using, and I'm not certain what frequency you're considering operating it at - perhaps 1MHz with a rise/fall time of 2ns?

    Board layout would be critical at high frequencies. The gate charge requirement for the MOSFET will act like a small capacitor, and the trace from the gate driver to the gate will have inductance, creating a series-resonant circuit that will ring like a bell when you place a fast-changing signal on it.
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Like Sgt. says keep driver as close to the mosfet as possible. On application note I think it was from International Rectifier said to keep the driver under 5/8 inch from the gate. And same note said a 4.7ohm to 25ohm resistor is what to use.

    Again like Sgt. said, to stop "ringing" on the gate, which is very bad for the mosfet.
     
  8. vivek20055

    Thread Starter Member

    Nov 4, 2012
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    Hello Shortbus,

    Thanks for your reply.

    Can you provide me the link for data sheet of International rectifier that contains the note of Rgate.


    Best regards,
    Vivek Alaparthi.
     
  9. shortbus

    AAC Fanatic!

    Sep 30, 2009
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  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I don't see an LM5112 in your schematic.:confused:
     
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