# POWER AMPLIFIERS

Discussion in 'Electronic Basics' started by Paul Burridge, Dec 1, 2005.

1. ### Paul BurridgeGuest

Oh please do. We don't get unsolicited lectures very often. ;-)

2. ### techproGuest

an amplifier circuit which uses power transistor is called power
amplifier .the are classified based on conduction angle.there are four
categorizes of power amplifiers they are
class A- conduction angle 360degrees
class B-conduction angle 180degrees
classC-conduction angle less than 180degrees
classAB-conduction angle more than 180 degrees
further classA is classified into
1.series fed class A power amplifier .
2.transformer coupled class A power amplifier.
SERIES FED CLASSA
it is called series fed because output is connected in series.
*the output signal is the exact replica of the input signal and has
less distortions.
*it has very less efficiency and has maximum efficiency of 25%.
the efficiency is less because in circuit we have resistor at collector
of transistor due to voltage drop across this resistor we have less
efficiency.
to overcome this disadvantage we go for transformer coupled classA
where we use transformer in place of resistor of seriesfed due to which
voltagedrop reduces and efficiency increasesand it has a maximum
efficiency of 50%.
I would like to discuss this topic later.

thank u,

4. ### techproGuest

as discussed earlier we use transformer in place of resistor to improve
impedance matching can be achieved because the transformer has primary
and secondary windings .by adjusting the values of the resistors placed
at input and output say R and R1 the ratio of windings can be achieved
as it depends on the following relation,i.e
R=R1(N\N1).
where N and N1 are primary and secondary windings.
a)the output signal is distorted as id contains
1.)harmonic distortation.
this is due to nonlinearities present is transistor or active
devices(BJT,FET,etc)
2.)phase distortion.
this is due to mismatch of phase angle.
3.)frequency distortion.
this is due to difference in frequency at input and output.
b)less efficiency
To over come these disadvantages we go for CLASS B
power amplifier.

5. ### PeteSGuest

---Rest of self serving lecture snipped-----

For want of a better term, you are full of Excrement of Male Bovine
(EoMB, as suitable acronym).

With credits and apologies to Tim Bray as original author of the term.

Perhaps your pixel persona might better be techdoh.

Cheers

PeteS

6. ### PeteSGuest

Interestingly, this looks suspiciously like a Q&A session from a basics
book

Cheers

PeteS

7. ### Guest

Just go BUY one you like and have a Merry Christmas.
GG

8. ### techproGuest

sorry,
it was the basic knowledge wat i had in this topic .may be it was like
ques and answer section but i felt that it can be disscussed better
only this way,if any more idea please suggest.thank u.

9. ### Charles SchulerGuest

Transformer coupled amplifiers at audio frequencies are obsolete.

Bridge-tied amplifiers are worth looking at as are Class D amplifiers, if
you are after the best efficiency possible.

If you are into linear stuff, the Class AB types with heavy negative
feedback and current limiting are good.

10. ### Bob MyersGuest

Nope; a "power amplifier" is either (a) an amplifier which
is used to obtain a significant gain in power, output vs. input
or (b) more colloquially, the output stage of a circuit, intended
to deliver significant power into the load. Amplifiers are
not classed by the type of devices from which they are
constructed. (I take it the finals at our old college radio
station wouldn't have been considered "power amplifiers"
per the above, since they used tubes rather than "power
transistors"? )
Nope; AB is more than 180 BUT LESS THAN 360;
you can't forget that final qualifier. And actually, the
above classifications are not, strictly speaking, limited to
"power" amplifiers (although they'd most often be seen in
that context.
Why would you think that only Class A amps can be
distinguished in this manner?
With what, Einstein?
The goal of any amplifier (esp. all Class As), not a distinguishing
characteristic.
That max. efficiency is generic to Class As, too.
OK - but find a better book to swipe your material from first.

Bob M.