Velleman DCA75 - Manual (Page 15)

Atlas DCA Pro User Guide December 2012 – Rev 1
Page 15
HFE=167
at IC=5.00mA
Current Gain (H
FE
)
DC current gain (H
FE
) is the ratio of the
collector current (less leakage) to the
base current for a particular operating
condition.
The DCA Pro measures H
FE
at a
collector current of nominally 5.0mA
and a collector-emitter voltage of
between 3V and 9V.
The gain of all transistors can vary
considerably with collector current,
collector voltage and also temperature.
The displayed value for gain therefore
may not represent the gain experienced at other collector currents and voltages.
This is particularly true for large devices.
The displayed value of gain is very useful however for comparing transistors of
a similar type for the purposes of gain matching or fault finding.
Darlington transistors can have very high gain values and more variation of
gain will be evident as a result of this.
The current gain of germanium transistors can vary a large amount
with changes in temperature. Even the warmth from your fingers can
alter the gain of a germanium device.
It is quite normal for transistors of the same type to have a wide range
of gain values. For this reason, transistor circuits are often designed so
that their operation has little dependence on the absolute value of
current gain.
IC=5.0mA
I -I
(I = leakage
current)
C Cleak
Cleak
HFE =
IB
IB