Velleman DCA55 - Manual (Page 15)

Atlas DCA User Guide October 2007 – Rev 7
Page 15
Current Gain (H
FE
)
The DC current gain (H
FE
) is displayed
after any special transistor features
have been displayed.
DC current gain is simply the ratio of
the collector current to the base current
for a particular operating condition.
The Atlas DCA measures H
FE
at a
collector current of 2.50mA and a
collector-emitter voltage of between
2V and 3V.
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.
Darlington transistors can have very
high gain values and more variation of
gain will be evident as a result of this.
Additionally, 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.
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.
Current gain
H
FE
=126
Test current
Ic=2.50mA
IC=2.50mA
IC
HFE =
IB
IB