Velleman DCA55 - Manual (Page 13)

Atlas DCA User Guide October 2007 – Rev 7
Page 13
Additionally, many Darlingtons and a few non-Darlington transistors also have
a resistor shunt network between the base and emitter of the device.
The Atlas DCA can detect the resistor shunt if it has a
resistance of typically less than 60kΩ.
The popular Motorola TIP110 NPN Darlington
transistor contains internal resistors between the base
and emitter.
When the unit detects the presence of a
resistive shunt between the base and
emitter, the display will show:
Additionally, the Atlas DCA will warn
you
that the accuracy of gain
measurement (H
FE
) has been affected by
the shunt resistor.
It is important to note that if a transistor does contain a base-emitter
shunt resistor network, any measurements of current gain (H
FE
) will be
very low at the test currents used by the Atlas DCA. This is due to the
resistors providing an additional path for the base current. The
readings for gain however can still be used for comparing transistors
of a similar type for the purposes of matching or gain band selecting.
The Atlas DCA will warn you if such a condition arises as illustrated
above.
Resistor shunt
between B-E
H
FE
not accurate
due to B-E res