BJT Flashcards
THE BRAINS
OF ELECTRONICS
TRANSISTORS
What was the electronic device of interest and development during 1904 to 1947?
Vacuum tube
What year was the vacuum tube introduce?
1904
Who introduced the vacuum tube?
J.A Fleming
What year did the control grid was added?
1906
What is the third element?
Control grid
Who added the third element?
Lee De Frost
The first amplifier
Triode
What is the negative effects of vacuum tube?
They were indispensable but they were large, short lived and consumed a lot of power.
What is the 1st computer?
ENIAC
How many vacuum tubes were used in e n i a c?
18000
What is the effect of overheating a vacuum tube?
black stain on the inside of the glass tube
Meaning of eniac
Electronic Numerical Integrator and Computer),
Who are the three engineers?
John Bardeen, William Shockley, and Walter Brattain
what principle did the three engineers used?
amplifying an electrical current using a solid semiconducting material, silicon,
When did The 3 demonstrated the amplifying action on the first transistor.
December 23, 1947,
The advantages of transistor over the tube where immediately obvious:
It was smaller and light weight. No heater requirement or heater loss. Had rugged construction. More efficient since less power was absorbed by the device itself
It was instantly available for use, requiring no warm up period.
Low operating voltages were possible.
A Bipolar Junction
Transistor (BJT) is composed of
three terminals connected to three doped semiconductor regions.
In an NPN transistor,a
thin and lightly doped
P-type material
is
sandwiched between two
thicker N-type materials.
While a PNP transistor,
a thin and lightly doped
N-type material is
sandwiched between two
thicker P-type materials.
The term bipolar reflects
the fact that
holes and
electrons participate in the
injection process into the
oppositely polarized
material.
The basic operation of transistor will now be
described using the
NPN transistor.
The figure shows the
proper bias arrangement
for NPN.
Notice that the
base-emitter junction
is
forward-biased
The figure shows the
proper bias arrangement
for NPN.
Notice that the base-collector junction
reverse-biased.
The figure shows the
proper bias arrangement
for PNP.\
Notice that the
base-emitter junction
forward-biased
The figure shows the
proper bias arrangement
for PNP.
the
base-collector junction
is
reverse-biased.
Notice that in both cases, the BE
junction is
forward-biased
Notice that in both cases,Notice that in both cases,
reverse-biased.
What happens inside the NPN transistor?
The forward bias from base to emitter
narrows the BE depletion region, and the
reverse bias from base to collector widens
the BC depletion region.
The heavily doped n-type emitter region is
teeming with conduction band (free)
electrons that easily diffuse through the forward-biased BE junction into the p-type base region where they become minority carriers, just as in a forward-biased diode.
NPN
transistor
The base region is lightly ______ and ______ so that it has a ________
doped, very thin, limited
number of holes.
The base region is lightly
doped and very thin so
that it has a limited
number of holes.
Thus,
only a small
percentage of all the
electrons flowing through
the BE junction can
combine with all the
available holes in the base.
These ______________, forming
the
relatively few
recombined electrons flow
out of the base lead as
valence electrons,small base electron
current.
Most of the electrons
flowing from the emitter
into the thin, lightly doped
base region _________________
do not
recombine but diffuse into
the BC depletion region.
Once in this region they
are pulled through the _________by the electric
field set up by the force of
attraction ______
reverse-biased BC
junction, between the
positive and negative ions.
The electrons now move
through the _____, out through the __________ and into the
collector region,collector lead, positive terminal of the collector voltage source.
Notice that the arrow on the emitter of the transistor symbols points in the
direction of the conventional
current.
These diagrams show that
the emitter current (IE)
is the sum of the collector urrent and the base current
IB is small compared to
IC and IE
DC Beta,
The ratio of the DC
collector current IC to the
DC base current IB
DC Beta,
current gain of a
transistor.
