Atlas DCA User Guide
October 2007 – Rev 7
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:
Resistor shunt
between B-E
Additionally, the Atlas DCA will warn
you that the accuracy of gain
measurement (HFE) has been affected by
the shunt resistor.
HFE not accurate
due to B-E res
It is important to note that if a transistor does contain a base-emitter
shunt resistor network, any measurements of current gain (HFE) 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.
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