Re: Help with amplifier output!

On Apr 5, 12:17 pm, "Bob" <nimby_NEEDS...@xxxxxxxxxxxxxx> wrote:
"Himlam8484" <creativeperson8...@xxxxxxxxx> wrote in message

news:1175749043.773718.62000@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx



Hi people,

I make a amplifier circuit. In my design, i connect some transistors
( type PNP) to increase the current output by connecting all of them
common base, Emitter to vcc( all transistors were droven by another
transistor). The current output is ok, but the signal output
reversed the phase. I would like to take a signal with the same phase
with input signal.

Can anyone know how to connect transistor together to increase the
current, but not change the phase?

I am looking forward hearing from people,

Lam

If you want current gain and no phase inversion, with one stage of
transistors, then you'll need "common collector" configuration.

For your PNP devices, hook the collectors to your minus supply. Tie the
bases together. Each emitter will need a separate small resistor (to insure
that the current shares equally), and tie the other end of all the resistors
together. This will be your output.

The problem with this simple configuration is that you can only provide
(sink) current from your minus supply. You have two options for being able
to also source current from your positive supply -- add a (high power)
resistor from the emitter resistors to the positive supply, or add another
group of NPN devices, in a similar configuration as your PNPs, with their
collectors to the positive supply.

The (high power) resistor approach will force you to run the amplifier in
what's called "class A" operation. The latter approach can be run "class B"
, "class AB", or "class A".

You should research the available literature describing high power amplifier
configurations and design.

Bob

Hi Bob,

First, thank you for your reply. I forgot to tell you that i added
another
group of NPN devices. Now i will remake it following your idea. If
having any problems, may you help me again?

Thanks,
Lam

.

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