Electronics Forum / Basics / April 2007

Just look at the transistor symbol. Obviously the emitter is heavier,
so it settles down to ground.

But I'm still confused about PNP's. I figure the emitters must be
helium implanted, since they tend to go up.

John

Ahem !

Graham

Man, do you have a lot of wonderful things to learn about
transistors.

Any configuration with more power out than power in has gain.

CE, CB and CC can all have power gain.

I don't know where to start.  CB puts the input impedance in
the output circuit as negative feedback.  This makes the
output more linear (less like a switch).

Good.  And that current gain at unity voltage gain
represents real power gain.

Of course, they do.  CB amplifiers can produce voltage gain
and CC can produce current gain.  That is getting a bigger
signal (in a power sense) out than you put in.

Now this is a roundabout way to force us to do the guy's homework.

Common base are used when one wants to do impedance transformation.  So
when you want to use that 8 ohm speaker as a microphone, you use a common
base amplifier because the low impedance input will better match the
microphone, and you will get some gain as well as a higher output impedance.

One should point out that common base amplifiers are not uncommon in
radio work, because they do that impedance transformation and because
their relatively low gain is a good thing.  If it had more gain, it
would require more effort to ensure that it wasn't unstable.

    Michael

Common-base has the same voltage gain as common-emitter, and it's just
as linear and sometimes more stable.

John

It most certainly is not.  Take a look at the output stage
of most audio amps, and get back to us, OK?

(Hint:  "amplifier" does not necessary equate to "voltage gain.")

Bob M.

Anyone else want to point out my ignorance and that I must have an IQ of -3?
By amplification I ment voltage amplification... I thought it would be clear
because usually that is how they are configured. A unity gain buffer is
unity in voltage but you don't say a unity gain voltage buffer? When you
talk about amplification it is almost always in the context of voltage
amplification? If you talk about current "amplification" it is almost always
talked about as current "gain"?

Also, aren't all transistors configured for power gain? wouldn't it be
worthless if both voltage and current decreased?

I was wrong about the CC and what I ment was a base biased configuration. I
was trying to give the 3 common modes that transistors are used as:
Switching, Amplification, and buffering.

Now amplification means voltage amplification because buffering is current
"amplification".  If not then why call it a unity gain buffer and not a
current amplifier?  Ok, maybe some people do but some of you have acted like
I commited a cardinal sin and it must mean I have no clue about what I was
talking about. In fact I was atleast 2/3 right and if you stop grading me
like a test then I might not be as dumb as some of you want to make me out
to be.  Maybe I got some termiology mixed up but it is enough to point that
out instead of trying to ridicule me.

Obviously if I said a switch it must be the configuration for a switch. i.e.
base biasing.  So just changed CC to Base biased and that fixes that
problem.  Just prefix all amplifications with voltage amplification and then
that fixes the other issue.

I guess 10 more people are going to reply to my original and say the same
stuff the last 10 said and call me a retard?  Now I really feel like a
retard. Thanks guys.

You know, its one thing to point out the mistake like John Larkin did and
its another to try and make the person completely feel like a retard even
when the mistakes are more about terminology than anything else. Maybe I
should have been more clear or re-read my post but its not like I'm writing
a thesis.  Sometimes I jsut get confused on the names cause I don't mess
with transistors much. Actually all I have ever did was a simple *voltage*
amplifier. I have read about them and actually just got finished reading
again... but the details don't stay in my brain when I don't use them.  The
book I was reading only discussed CE and CB and base bias so I assumed CC
was that base bias because I recalled that there were only 3 configurations.
I'm going to have to see exactly how CC works now to see the difference.

On Apr 27, 12:51 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

I only remeber the dual gate fet that had a wire ring around all the
leads that you removed after the fet was installed. And if you wanted
to remove the fet from the circuit you needed to wrap some wire around
the leads to avoid static. But it never worked since the wire would
come loose and the thing was always dead when I got it back in the
circuit.

-Bill