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  1. #1
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    Mosfet Driver Vs BJT Driver

    Hello Friends ,

    i want drive a mosfet in 10khz PWM 10v 2A IRFP240

    i should use IR drivers series or i can make simple driver with BJT PNP NPN ?

    What is the advantage of a gate driver over this circuit?
    i don't need isolation

    Click image for larger version. 

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    *Values are incorrect and not calculated

    Thanks a lot

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    Re: Mosfet Driver Vs BJT Driver

    The circuit doesn't work. Q1 is permanently turned on. Even with 5V supply, it's prone to cross-conduction.


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  3. #3
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    Re: Mosfet Driver Vs BJT Driver

    It's not necessary this circuit.If the Fanout Capacity of the PWM Source sufficient, you can directly drive the MOS if the signal swings between 0-5V..
    Otherwise use a simple Buffer from any mfg.


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    Re: Mosfet Driver Vs BJT Driver

    Put the npn on the top and the pnp on the bottom and you have an emitter follower, tie the bases together and use 100R resistor - for a 5V drive you will need a logic level fet or a level shift in your gate drive ckt ... to allow a 12V drive ...

    as you have drawn it - both xtors will be on - not so good ...


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    Re: Mosfet Driver Vs BJT Driver

    For simple circuits maybe this kind of thing suffices. Maybe
    even costs less although by the time you add in passives
    and board area, did you really win vs an IC MOSFET driver?
    Not likely on switching speed, drive strength or consistency.
    And this latter matters once you start working with half-
    and full-bridge designs where timing has to be kept right
    across the envelope. Or you want a control signal of much
    lower voltage than the high side power supply.

    The saturation of the bipolars will make switching messy
    (including some significant shoot-through in the BJY pair
    itself, which might impose a mid-range plateau on the
    gate beyond what it naturally wants to do (Miller) and
    cause excess dissipation in the driven FET.


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    Re: Mosfet Driver Vs BJT Driver

    The MOS Input Capacitance 8nF (max)!! It's really huge if the PWM frequency is relatively high.It will need a "strong" Driver for it.



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    Re: Mosfet Driver Vs BJT Driver

    Hi,

    Driver ICs are optimaized for their application ... hard to achive the same performance with discrete parts.
    Part count, cost, development time, reliability, additional features in the ICs....
    Where is the benefit of the discrete solution?

    There is a good reason why most of the professional designers use ICs.

    Klaus
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