INTRO TO TRANSISTORS (study)
Input signals are either :
AC or DC •DC bias
Total current flowing through the transistor circuit (Ie) is found by:
Ie = Ib + Ic
The COLLECTOR is moderately doped.
It collects the current carriers from the base. The collector is the largest of the 3 areas because it has to dissipate most of the heat generated.
Transistors are solid state devices constructed from
N-type and P-type materials just like diodes.
There are two types of transistors:
NPN and PNP
high resistance junction.
Placing a large positive voltage on the collector reverse biases the collector to base PN junction
low resistance junction.
Placing a positive voltage on the base and a negative voltage on the emitter forward biases the emitter to base (EB) PN junction
Transistors are marked with identification numbers. 2N3304
The "2" indicates a transistor (two PN junctions). The "N" indicates a solid state component. The last digits identify the type of transistor.
Most transistors' leads are arranged in a semicircle.
The base lead is in the middle. The emitter is on the left The collector is on the right
The purpose of a transistor is to control signals.
Transistors control a large signal with a small signal.
Transistor bias is accomplished by
forward biasing the emitter to base PN junction (EB) and reverse biasing the collector to base PN junction (CB).
Current flows from the emitter to the collector because
he base is thin and lightly doped.
.The schematic symbol is
is Q.
Current does not flow from the base to the collector; the PN junction is
is reverse biased.
a forward biased diode has a
lower resistance than a reverse biased diode.
Power transistors are different. The collector is connected to the
metal case of the transistor.
The collector receives
most of the current carriers.
In a PNP transistor, the base DC bias voltage must be
negative compared to the emitter
In an NPN transistor, the base DC bias voltage must be
positive compared to the emitter
The input is the signal that is changed to
produce an output
The BASE is very thin and lightly doped
so Its construction allows most of the current carriers to pass from the emitter to the collector.
The EMITTER is heavily doped
so it produces (emits) a large number of current carriers inside the semiconductor material.
Transistors are
solid state devices constructed like diodes.
DC biasing is the signal tha tallows
the transistor to operate.
The emitter voltage is developed by the action of
the transistor. Most bipolar junction transistors require 0.6 V to forward bias the base-emitter PN junction. Ee=Eb - 0.6 V
The arrangement of the elements determines
the type of transistor.
Unlike diodes, transistors have
three elements with two PN junctions.
The emitter produces current carriers.
•Electrons in N-type material •Holes in P-type material
Transistors are used as:
•amplifiers •oscillators •electronic switches
