Andre Abelian wrote:
> Based on my understanding bipolar transistors pnp or npn they are
> normally off until apply voltage to the base to turn it on

No, it take current thru the base to turn on a bipolar transistor.

> but FET
> transistors are opposite they are normally on until apply power to the
> Gate and Source to turn it off.

First, it doesn't make sense to talk about power applied to the gate.  The
gate mostly looks like a capacitor to the rest of the circuit, so draws no
power at a steady voltage.  Second, even if you had said voltage it still
makes no sense to talk about applying it.  There is no such thing as no
voltage.  The question is only what voltage, and measured with respect to
what other circuit point.  Therefore "applying" a voltage doesn't tell me
what the voltage is, what it was before, and measured with respect to what.

FETs are controlled by the voltage on the gate with respect to the source.
Whether a high voltage is on and a low voltage off or the other way around
depends on whether it is a N or P channel FET and whether it is a
enhancement mode or depletion mode part.

Most ordinary N channel MOSFETs are off at 0V G-S and on at 12V or so G-S.
Some, sometimes called "logic level" are designed to turn on well with 5V
G-S or even lower.


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