see in the specification sheet for a darlington transistor
It depends on the concept you're trying to understand. If you
simply want to have an idea of the maximum voltage that can be
applied between collector and emitter before breakdown,
assuming
that the polarity is in the usual direction, then it could be
said that they are the same.
However, to be technically correct and also specify the
polarity
at the same time, they are not the same. For example:
The voltage applied to the collector of an NPN transistor is
normally positive with respect to the emitter. Therefore, the
collector-emitter voltage (whether breakdown or normal
operating)
would be given as X volts, whereas for a PNP transistor, it
would
be -X volts.
If you give X volts as the emitter-collector voltage, it would
mean that the emitter is positive with respect to the
collector.
This is the reverse of the way an NPN transistor is normally
operated. The breakdown voltage would also probably be
different
because the base-emitter junction and the base-collector
junctions are made different in practice, although their basic
principles are the same.
Let me add some clarification to my earlier statement.
The darlington transistor is an NPN device used as a low side
switch.
Emitter is tied to ground. I am interested in understanding what
happens when the collector goes negative with respect to ground.
In this instance, wouldn't the emitter to base junction break
down
first (max rating of 10V)? Current would flow from the emitter,
to
the base, then from the base to collector (one diode drop). So,
total
breakdown voltage in the reverse direction (assuning the
connection
scheme listed above) would be approximately 10.7VDC?
Yes, that's what would happen unless the base is prevented from
being pulled below ground by some other circuitry. This can be
qualitatively demonstrated with a single (non-darlington)
transistor and an analog multimeter set at the high ohmmeter
range. The 9V battery generally used to drive the high resistance
range is higher than the e-b breakdown voltage (usually around
5V). In fact, I often use this to identify the leads of an
unknown transistor. The collector-emitter path is essentially
open in one direction, but conducts in the other direction, but
at a lower level than a single p-n junction.
