1. The document discusses the basic operation of a BJT transistor. It explains that for a BJT to operate as an amplifier, the base-emitter junction must be forward biased and the base-collector junction must be reverse biased, known as forward-reverse bias. 2. It describes how electrons diffuse through the forward-biased base-emitter junction and into the base region, and then into the reverse-biased base-collector depletion region where they are pulled through by the electric field. 3. It shows that the emitter current is the sum of the collector current and the base current, with the base current being much smaller than the collector current.

1. 2017
Technical Trainer
College
Eng.Nawaf
[TRANSISTOR]
MOHAMMAD ALMALKI202633044

2. 1.1 BASIC BJT OPERATION:
Chapter 1
3
1.1 BASIC BJT OPERATION
 In order for a BJT to operate properly as an amplifier, the two pn junctions
must be correctly biased with external dc voltages.
Biasing
The figure shows a bias arrangement for both npn and pnp BJTs for operation as
an amplifier.
Notice that in both cases the base-emitter (BE) junction is forward-biased and
the base-collector (BC) junction is reverse-biased. This condition is called
forward-reverse bias.

3. Chapter 1
Operationof npn transistor BASIC BJT OPERATION
 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,
 electrons can easily diffuse through the forward-biased BE junction into the p-
type base region, just as in a forward-biased diode.
 only a small percentage of all the electrons flowing through the BE
junction can combine with the available holes in the base (base is thin and
lightly doped)
 then electrons diffuse into the BC depletion region. Once in this region
they are
pulled through the reverse-biased BC junction by the electric field set up by the
force of attraction between the positive and negative ions.

4. Chapter 1
Transistor Currents BASIC BJT OPERATION
) is the sum of the collectorE
current (IThese diagrams show that the emitter
), expressed as follows:B
current (Ic) and the base current (I
B
+ IC
= IE
I
letter subscripts indicate-. (The capitalC
or IE
is very small compared to IB
INote:
dc values)

5. 1.2 Transistor Characteristicsandparameters
Chapter 1
1.2 Transistor Characteristics and parameters
Two important parameters are used to analyze transistor circuit:
 ßDC
(dc current gain )
 αDC
The dc current gain of a transistor is typically 20 –
200 and given by:
) to the dc emitter currentC
The ratio of the dc collector current (I
0.99 and is given by:–) is typically ranges from 0.99E
(I
DC
ßNote:
varies with
temperature
.C
and I