> > I thought I read collector has to be more positive than
> > base and base has to be more positive than emmitter,
> > or transistor would be off. Apparently I am mistaken.
>
> A saturated transistor's E-C voltage is typically 200mV, while the E-B
> voltage of an "on" transistor is one diode drop, around 700mV.  When the
> transistor is on but not saturated, the collector can be much higher.  In
> any case, it's the base current that decides whether the transistor is
> "on", not the collector current or voltage.

Olin is, of course, correct. But a point of clarification.
When the transistor is on, the collector can be LOWER than the base voltage
under the on conditions mentioned above.
This can be deduced from the above but is somewhat unintuitive and some
people do not realise that this can happen.

As Olin says, when the base is driven on it rises to around 0.6 to 0.7 volts
relative to emitter.
The collector can go essentially to emitter voltage plus saturation voltage.
If the saturation voltage is less than Vbe then collector voltage will be
below base voltage.


        RM

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics