[Elecraft] K2 transistor questions

Fri Jan 16 20:56:01 2004

They are two different technologies, John:

A "bipolar" transistor has two diode junctions: one between the base and =
the
collector that is normally reverse biased and one between the base and =
the
emitter that is normally forward biased. A small amount of current is
allowed to flow into the base, through the junction to the emitter and =
back
to the supply. As this current increases, a surprising thing happens to =
the
collector current. As the base current increases a corresponding but =
much
LARGER change in current through the collector-emitter path occurs, so =
the
bi-polar transistor amplifies.=20

A "field effect" transistor has a current flow between the drain and =
source.
This current flow is controlled by a VOLTAGE at the "gate" which acts =
like a
gate. As the voltage on the gate changes, it controls the current flow
between drain and source. There are several types of "field effect"
transistors, but they all feature very low gate current, so they are a
"voltage-controlled" device rather like a vacuum tube. The amount of =
current
flowing in the gate is miniscule. Many FET's show an input impedance
(resistance) in the tens or hundreds of megohms. By comparison, a =
bi-polar
transistor might show a base impedance (or resistance to the d-c bias) =
of
only a few tens or few hundreds of ohms.=20

They both have significant advantages in various circuits, so it's =
common to
see both used in a typical rig.=20

Ron AC7AC

-----Original Message-----
From: [email protected] =
[mailto:[email protected]]
On Behalf Of John Cooper
Sent: Friday, January 16, 2004 5:17 PM
To: [email protected]
Subject: [Elecraft] K2 transistor questions

Could some one kinda explain why some are collector base and emitter and
some are drain source gate( I think thats what they stand for) ?  Hoping
someone has time to enlighten me. =20

WT5Y