| rtarbell |
For a large switching FET, in order to get the FET to switch quickly and to avoid excess power consumption, a large Vgs (usually >10V) must be supplied, along with a fair amount of current behind that Vgs supply (~1 amp of transient current for a large FET).
What is the difference between gate capacitance and gate charge, in terms of how much gate current/gate-source voltage needs to be applied? I thought the measure to be concerned about when switching a FET was gate charge, but how does gate capacitance come in to play? |
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| cliff |
The two are related.
It is Gate voltage which controls the D/S channel conductivity, but to get the gate to required voltage requires charging up the gate capacitance.
A useful formula is q = CV = IT (q = charge)
So if there is a high gate C, (large geometry) either Time is required (slow) or a large Current to charge it.
Think about the CV=IT bit.
It is very useful in understanding the relationships between C, V, I, T. linked by the concept of charge. |
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