Velleman DCA55 - Manual (Page 18)

Atlas DCA User Guide October 2007 – Rev 7
Page 18
Enhancement Mode MOSFETs
MOSFET stands for
Metal Oxide Semiconductor Field Effect
Transistor. Like bipolar transistors, MOSFETs are available in
two main types, N-Channel and P-Channel. Most modern
MOSFETs are of the Enhancement Mode type, meaning that
the bias of the gate-source voltage is
always positive (For N-Channel types).
The other (rarer) type of MOSFET is the
Depletion Mode type which is described
in a later section.
MOSFETs of all types are sometimes known as IGFETs, meaning
Insulated
Gate Field Effect Transistor. This term describes a key feature of these
devices, an insulated gate region that results in negligible gate current for both
positive and negative gate-source voltages (up to the maximum allowed values
of course, typically ±20V).
The first screen to be displayed gives information on the type of MOSFET
detected. Pressing scroll-off will then
result in the pinout of the MOSFET being
displayed. The gate, source and drain are
each identified.
An important feature of a MOSFET is the
gate-source threshold voltage, the gate-
source voltage at which conduction
between the source and drain starts. The
gate threshold is displayed following the
pinout information.
The Atlas DCA detects that drain-source conduction has started when it
reaches 2.50mA.
Enhancement mode
N-Ch MOSFET
RED GREEN BLUE
Gate Drn Srce
Gate Threshold
Vgs=3.47V
Test current
Id=2.50mA