MOSFET Question: Vgs(th) vs. Drive Voltage

Can anyone tell me the difference between the drive voltage and the gate-to-source threshold voltage (Vgs,th) of a MOSFET, if any?

I was under the impression that these refer to the same voltage - the voltage that is needed to turn the MOSFET 'on'. However, if you look at the following datasheet for a Fairchild MOSFET...

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you'll see that the title says "2.5V Specified", which I understand refers to the drive voltage. However, under the "On Characteristics," you'll see Vgs(th) min. = 0.4V and Vgs(th) max. = 1.5V. Why isn't Vgs(th) max. = 2.5V, as the title suggests? Is there a difference between Vgs(th) and the "specified voltage"?


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Vgs(th) is the threshold of conduction, usually is defined as the voltage necessary to turn the FET barely on, that is at some defined small current like 100uA.

The drive voltage is the voltage necessary to turn the FET *really* ON. Saturated and able to carry the rated current and exhibit the rated RDSon.

Is all in the datasheet.


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