VBC of npn transistor in common collector mode
- From: "John B" <jb@xxxxxxxxxx>
- Date: Thu, 6 Jul 2006 07:55:03 -0700
For a typical npn bipolar transistor, such as the 2N2222A, we can expect a
DC voltage drop of about 0.65 V, from base to emitter ("V BE"). Such is the
case of the ubiquitous "common emitter" configuration.
Suppose we flip the transistor, and use it "backwards." Let's call this,
"common collector." Correct me if I'm wrong, but that sounds like the
accurate description of the configuration, because we are grounding the
collector, driving the base with a controlling current, and attaching a
pulled-up load to the emitter. This is an inverting amplifier...sort of.
Beta can be expected to be "miserable," with a value of less than 1, instead
of roughly 100. So amplification is "in the eye of the beholder." Granted.
Can anyone advise on the forward voltage drop of between base, and ground?
(That is, "V BC") I expect that the collector is very lightly doped,
compared to the emitter, so the barrier should be far less, leading to a
lower threshold voltage to overcome.
Thanks in advance.
.
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