FET Transistors

[Rene Schmitz]

>Most jfets are symmetrical regions of semiconductive N or P type
>material, the "source" and "drain" being nominal designations of
>the ends of the region. The gate is an abutting region of the
>opposite type of material.
>
>USUALLY ... the gate will conduct like a diode when forward
>biased to either source or drain. No surprise - it IS a forward
>biased diode.
>[...]
>So. Find a lead that conducts to both others. That's the gate.
>If there is one that has a higher resistance from the gate, that
>is likely to be the drain.

That is true for Junction FET's like the BF245,
but absolutely non true for MOS-FET's like the BUZ10, BS250.
In case of the MOS-FET there is an isolating layer between the 
Gate and the part where drain and source are connected to.

(BTW: Thats where the name metal (=gate) oxide (=isolator) semiconductor
came from)

In that case you will find one lead of the FET that will have a high resistance
measured to the others.
You can (mostly) determine which of the leads is the drain and which one is the 
source because most of the MOS-FET's have backward diodes, that means the
cathode of the
diode is connected to drain.(Assuming the FET is an N-type)


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