Post on 29-Dec-2015
transcript
TRANSISTOR
A transistor is a semiconductor device used to
amplify and switch electronic signals and electrical
power.
The transistor is the fundamental building block of
modern electronic devices
There are two types of transistors
Bipolar Junction Transistor Field-effect Transistor
Bipolar Junction Transistor
Bipolar junction transistor (BJTs) is made by three doped semiconductor region
separated by two pn junctions sown in figure 1.
The term bipolar refers to use both the holes and electrons as carriers in the
transistors structure.
There are two types of BJTs
npn (two n-regions separated by a p region)
pnp (two p-regions separated by a n region)
Figure-1 Basic BJTs construction
BASIC BJTs CONSTRUCTION
The pn-junction joining the base region and emitter region is called base
emitter junction
The pn-junction joining the base region and collector region is called base-
collector junction
A wire lead is connected to each of three region. These leads are labeled
E, B and C for emitter, base and collector respectively as shown in figure-1
(b).
The base region is highly doped as compare to heavily doped emitter and
moderately doped collector regions
Figure-2 standard BJTs symbols
BASIC BJTS OPERATION
Base- emitter junction is forward bias Base collector junction is reverse bias
BJTs Currents and Voltages
Voltage across RB is
By Ohms law
The value of IB is then
Voltage at collector
Voltage across RC
Then the voltage at collector
The voltage at reverse bias collector base junction
DC Beta(βDC)b
The ratio of collector current to base current is the current gain of transistors and is given by
Typical values of βDC ranges from 20 to 200.
The ratio of collector current to emitter current is the dc αDC and is given by
The values of αDC range from 0.95- 0.99 but always less than 1.
Dc Alpha (αDC)
Problem-1
Determine IB, IC , IE, VBE, VCE, and VCB in the following circuit (βDC = 150)
Solution-1
Problem-2
Determine IB, IC , IE, VBE, VCE, and VCB for the following circuit values (βDC = 90)
RC = 220 Ω
RB = 22 k Ω
VCC = 9V
VBB = 6V
Problem-3 Determine values of IE and βDC for a transistor whereIC = 3.65 mA IB = 50 µA