mosfet are not based on current, not like BJT.. they use the voltage applied on gate as a reference.
the most commun is put a high value resistence in gate.
search for how mosfet works on web, may answer your doubts.
the steps that the mosfet goes through while conducting are shown inthe next image (from page 17 of https://www.fairchildsemi.com/an/AN/AN-9010.pdf ),
View attachment 56675
The output current is shown with green, the voltage drop across the mosfet is shown in blue.
The X axis shows the different stages while the mosfet capacitance gets charged
Between t1 and t2 the output current goes from 0 to the max , in that point you still have the max voltage drop across the source-drain and also the max current through the mosfet that means many watts as heat (V*I).
As the charge stages go on you see that the voltage drop across the mosfet lowers at the t2 to t3 stage where it goes almost to 0
You want to provide high current to the gate to go through that stages as soon as possible because the part from t0 to t3 is a high power consumption stage.
You can either do that id a few nano seconds or it can take many us and even ms.
Also note that the mosfet goes through this stages when it turns off too and consider that it goes through them 40000 times per second with a PWM of 20kHz (20000 times on and 20000 times off)
Alex
I think, you can omit two components, place a short instead and get basically the same effect: The current will be only limited by the processor output driver, and surely exceed the specified maximum values.what do you think about adding a cap in parallel with the resistor ?
Not when driving a MOSFET gate. But the characteristic doesn't apply to all processor ports. There are many, that are able to source or sink current above maximum ratings. If not, the current limiting resistor discussion would be void.FvM , can he get more current that the max shown in the output graph of the datasheet or this graph applies in any case?
Not when driving a MOSFET gate. But the characteristic doesn't apply to all processor ports. There are many, that are able to source or sink current above maximum ratings. If not, the current limiting resistor discussion would be void.
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