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    calculating capacitance of transistor gates

    Is it as simple as C= V/Q for this part maximum gate capacitance at 15v would be 119e-9/15 yeilding 7.93nF?



    https://www.st.com/content/ccc/resou...DM00052344.pdf

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    Re: calculating capacitance of transistor gates

    Hi,

    I'm not sure what your question is...

    The output capacitance is acting as miller capacitance, thus ...
    * Although the voltage at the gate changes only about 15V
    * the voltage at the output capacitance may change 415V.
    This causes high Q.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.


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    Re: calculating capacitance of transistor gates

    Quote Originally Posted by KlausST View Post
    Hi,

    I'm not sure what your question is...

    The output capacitance is acting as miller capacitance, thus ...
    * Although the voltage at the gate changes only about 15V
    * the voltage at the output capacitance may change 415V.
    This causes high Q.

    Klaus
    Hence max gate charge was determined at 415Vds was to obtain Vgs capacitance to obtain peak current which apparently is 7.93nF for 15Vgs at specified Ids.



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    Re: calculating capacitance of transistor gates

    I don't understand the purpose of deriving a capacitance value from total gate charge, because there's no physical capacitor representing the charge. The real behavior is better characterized by Figure 8, gate charge vs gate-source voltage.

    Total gate charge can be used to easily calculate the per pulse gate driver energy and average gate driver supply current.


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    Re: calculating capacitance of transistor gates

    The effective input capacitance is calculated as in post #1. You have capacitance curves in the datasheet.


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    Re: calculating capacitance of transistor gates

    Total gate charge is useful to calculate switching losses
    but treating it as a fixed capacitance will not be accurate
    when it comes to transient switching behavior. Be sure
    you want the right things.


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    Re: calculating capacitance of transistor gates

    This was to determine peak Igs current for gate driver which is 7.93nF for mentioned part.



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    Re: calculating capacitance of transistor gates

    Peak current into gate of transistor is simply V_driver/Rgate. No need for any capacitance value.


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    Re: calculating capacitance of transistor gates

    Is Rgate the series resistor between gate driver output and transistor gate?



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    Re: calculating capacitance of transistor gates

    It includes the gate driver's resistance and transistor's internal resistance as well.


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