Manual

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 60k

Ω

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

) 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

) 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

not accurate

due to B-E res