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MOSFET rise time?

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p1120

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Hi all :p
I am a student in electronics.I was wondering if anyone could answer my question plz:
Regarding MOSFET switching times,how can we calculate its rise time?
I know that the rise time is the time that MOSFET takes as the gate-drain capacitance discharge and also I know how to calculate the rate of change of the drain-source voltage.I am just not sure having the values for gate-drain capacitance,gate-source capacitance,threshold voltage,the gate resistance(RGG) and Vcc.

Cheers.
 
Have a look at the datasheet for the MOSFET in question, it will actually tell you the rise and fall times.
 
p1120 said:
Hi all :p
I am a student in electronics.I was wondering if anyone could answer my question plz:
Regarding MOSFET switching times,how can we calculate its rise time?
I know that the rise time is the time that MOSFET takes as the gate-drain capacitance discharge and also I know how to calculate the rate of change of the drain-source voltage.I am just not sure having the values for gate-drain capacitance,gate-source capacitance,threshold voltage,the gate resistance(RGG) and Vcc.

Cheers.

The risetime of a circuit is governed by the RC time constant of the equivalent circuit. You must draw the equivalent circuit model for your type of MOSFET, and then do the calculation.
 
The real problem is that the calculation is not straightforward because there is non linear behavior. Drain current is a quadratic function of Vgs. If you look at an actual gate or a spice simulation you will notice a little plateau in the gate waveform. This plateau can be as much as 30% of the fall time. If you think about intrinsic capacitors of the device going from the gate to the drain and from the gate to the source and you realize that as the voltages at the drain and the source change they have an effect on the gate voltage you begin to understand the complexity of the problem.
 
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