The
2 opposing diode junctions of the emitter and collector are forward
biased when current flows out of the base in an NPN
and into a PNP transistor.
A small base current controls a much larger E-C current
which drives a load (speaker, solenoid, light, etc.)
The amplifying
action of a transistor starts with a signal from a transducer such
as a microphone, CD player, or process control instrument etc.
This signal is small but when fed to the base is enough to forward bias
the emitter/collector junction and allow current to flow in proportion to
the base current.
There are a variety of amplifier types but they all follow the same
principles.
Gain
is the term used to describe the amount of amplification that an amp is
capable of. (also called Beta or Hfe
)
example: if a 10 milliwatt signal from a microphone is amplified to a
1watt output then... GAIN
= Pout
/ Pin
= 1000mw / 10mw = 100
(no unit they divide out!!)
PUSH PULL AMPLIFIER
The class B Push Pull Amp is a
typical output stage of a power amplifie
Amplifiers
are often built up from 2 or more stages to enhance the
amplification. A preamp stage can be followed by a more powerful driver
output stage. An amp that uses both PNP and NPN transistors is the Push
Pull amplifier. The NPN transistor amplifies the positive side of the
wave and the PNP amplifies the negative side of the wave.
This 2 stage Push Pull Amp has 2 stages. Preamp and Power.
The capacitors at the input and output allow the alternately signal
current to "pass" through while stabilizing the transistor
circuits.
This audio
amplifier has 2 sections (left right channels) each with a
large power transistor.
The
heat sinks are to radiate heat from the
transistors.
transistor
do
you know how speakers work?
