Download WORKING OF scr….

PARUL INSTITUTE OF ENGINEERING &
TECHNOLOGY
Subject Code : 331101
Name Of Subject : Basic Electronics
Name of Unit : OSCILLATORS & AMPLIFIERS.
Topic :Hartely Oscillator & Colpitt oscillator
By :Mr. Harekrushna Avaiya
Circuit Explanation:






By:-Harekrushna Avaiya
Q is NPN transistor.
R1 and R2 are biasing resistor.
RE is the resistance connected
in the emitter.
CE is the bypass capacitor.
(L1+L2)C form the tank circuit.
RFC is the radio frequency
chocke which allows d.c to pass
through and offers high
impedance to a.c.
Oscillation energy developed
across the choke is coupled to
tank circuit by coupling
capacitor C2.
Working:


When power supply is
given,collector current flows
through the choke.
A.C. energy developed in the
collector circuit given to tank
circuit through coupling
capacitor Cc2.
Voltage developed across L2
is coupled to the base through
coupling capacitor Cc1..
Thus due to positive feedback and sufficient gain and
oscillations are produced.
COLPITTS OSCILLATOR







Q is NPN transistor.
R1 and R2 are biasing
resistor.
RE is the resistance
connected in the emitter.
CE is the bypass capacitor.
(C1+C2)L form the tank
circuit.
RFC is the radio frequency
choke which allows d.c to
pass through and offers high
impedance to a.c.
Oscillation energy
developed across the choke
is coupled to tank circuit by
coupling capacitor C2.
WORKING……



When power supply is
given , collector current
flows through the choke.
A.C. energy developed in
the collector circuit given
comes to tank circuit
through coupling capacitor
Cc2.
Voltage developed across
C2 is coupled to the base
through coupling capacitor
Cc1..
Thus due to positive feedback and sufficient gain and
oscillations are produced.
SILICON CONTROLLED RECTIFIER
SL

CONSTRUCTION:-

SCR is 4-layer,3-junction
and 3-terminal PNPN
semiconductor device.
Here, three terminal is
given as,
-Anode,
-Cathode &
-Gate




WORKING OF SCR….



Working of SCR can be
easily understand by two
transistor analogy.
If we divide the middle
two layers in two parts,
then
construction
becomes as shown in
figure.
Here, one PNP transistor
& other one is NPN
transistor.
WORKIONG OF SCR…

As shown in figure,
collector
of
first
transistor is connected
to base of second
transistor
and
the
collector of second
transistor is connected
to the base of first
transistor.
WORKING OF SCR…..



When anode is connected to positive supply and cathode is
connected to the negative ,and gate is not connected to any
supply, both the transistor are in OFF state , they offer very high
resistance and whole voltage is dropped in the SCR and output is
zero.
When a positive pulse is given to the gate , base current IB1 flows.
So, collector current IC1 flows. But the collector current IC1 of
transistor T1 is the base current IB2 of transistor T2. So, the IB2
flows and as a result , collector current IC1 flows. Now , this
current IC2 flows through the base of transistor T1.So,the
collector current IC1 increases. This is cumulative process. As a
result a large current is conducted by the device in very short
time, the resistance of the device decrease too much.
So ,load can be control by very small positive pulse in SCR.
Thus due to positive feedback and sufficient gain and
oscillations are produced.
THANK YOU