Re: FETs and MOSFETs

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Justin Hays by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pyrotrons2000-at-yahoo-dot-com>

Hi All,

FET is short for Field Effect Transistor, they are generally used for
small-signal (tiny signals from an antenna) amplification purposes in
radio circuits. There are many other uses, however. An example of a
common FET is an MPF102, which Radio Shack stocks.

A MOSFET is a different kind of FET, and stands for Metal Oxide
Semiconductor Field Effect Transistor. Generally speaking, MOSFET's
can handle more power than FET's or JFET's ("J" for Junction), and
are commonly used in linear amplifier circuits and switching
applications. If you need a bounceless switc that will go from "open
circuit" to "short circuit" in less than 20 nanoseconds, a MOSFET
will do it. Common MOSFET's are the IRF840 (500V 8amps) and the
IRF740 (400V 10amps).

All types of field effect transistor have at least 3 leads, one is
gate (the "control" pin), source, and drain. Some RF (high frequency)
transistors have two gate pins to ease circuit design.

But it does go deeper, there are different types of FET's, depending
on their internal silicon structure. They are N-channel, P-channel,
enhancement mode, and depletion mode types....it all depends on what
your circuit requires as to what FET type to use. For instance, if
you want to turn the transistor ON with some positive voltage (most
common application), you use an N-channel enhancement mode FET. 

It's very important to note that all types of FET are controlled by
voltage, and not current. 

The input impedance (gate to source) of a FET is extremely high,
making them very easy to work with because their input won't load
(pull current from) your circuit.

----

MMC's are the best capacitors for Tesla Coils, comparable to
commercially available pulsed-discharge rated capacitors such as
those made by Maxwell. MMC's consist of many small capacitors tied
together to get the required voltage/capacitance rating. By far the
best dialectric to use for pulsed discharge use (tesla coils) is
polypropylene.

And so ends my spiel...

Take care,

Justin Hays
KC5PNP
Email: justin-at-hvguy-dot-com
Website: www.hvguy-dot-com