Download T0 Design and Implement astable Multivibrator

To Design and Implement
Astable Multivibrator Circuit
Using IC555
LAB:- CEII (SEM V EXTC)
AIM
To Design and Study the operation of
astable multivibrator using IC555 Timer
LAB:- CEII (SEM V EXTC)
Apparatus
•
•
•
•
•
•
•
555 Timer IC
Resistor ( Values as per design)
Capacitors (Values as per Design)
Function Generator
CRO
Bread Board
Connecting Wires and Probes
LAB:- CEII (SEM V EXTC)
Theory
• Functional Block Diagram of IC555:-
Reference:- www.electronics.dit.ie
LAB:- CEII (SEM V EXTC)
Functional Block Diagram of IC555
• Timer IC consists of two comparators
• A resistive voltage divider generating the
required reference voltage for the two
comparator
• SR flip-flop
• Output Buffer
• Discharging Transistor T1
LAB:- CEII (SEM V EXTC)
Multivibrators
It is a circuit which can have no, one or two
stable states of operation.
Types :1. Astable Multivibrator:- No stable state
2. Monostable Multivibrator:- One stable state
3. Bistable Multivibrator :- Two stable states
LAB:- CEII (SEM V EXTC)
Astable Multivibrator using IC555
Fig 1. :Astable Multivibrator using IC555
Reference:- https://electrosome.com/astable-multivibrator-555-timer/
LAB:- CEII (SEM V EXTC)
Astable Multivibrator Working
• The astable multivibrator is also called as free running
multivibrator and does not require an external trigger for
changing the state
• The time constant of the externally connected two resistors(R1
and R2) and a capacitor C to IC 555 determines the ON and
OFF time of output waveform.
LAB:- CEII (SEM V EXTC)
Astable Multivibrator Working
• When the circuit is switched ON, the capacitor (C)
voltage will be less than 1/3 Vcc. So the output of the
lower comparator will be HIGH and of the higher
comparator will be LOW. This SETs the output of the
SR Flip-flop.
• Thus the discharging transistor will be OFF and the
capacitor C starts charging from Vcc through resistor R1
& R2.
• When the capacitor voltage will become greater than
1/3 Vcc ( less than 2/3 Vcc ), the output of both
comparators will be LOW and the output of SR Flip-flop
will be same as the previous condition. Thus the
capacitor continues to charge.
LAB:- CEII (SEM V EXTC)
Waveforms
Reference:-http://circuitdigest.com/electronic-circuits/555-timer-astablemultivibrator-circuit-diagram
LAB:- CEII (SEM V EXTC)
Design Equations
1.
2.
3.
4.
5.
Ton = 0.69(R1+R2) C
Toff = 0.69R2C
Ttotal= Ton + Toff = 0.69(R1+2R2)C
Frequency of oscillation = f= 1 / Ttotal
= 1.44 / (R1+2R2)C
Duty Cycle= Ton / Ttotal
LAB:- CEII (SEM V EXTC)
Design Statement for Implementation
Design an astable multivibrator using IC555 for f=5KHz
and duty cycle= 50%
Soln:f= 1 / Ttotal = 1.44 / (R1+2R2)C
Let C= 0.047uF
Hence R1+R2 = 6128Ὠ
D= R1/ (R1 + R2)
Hence R1 = 0.5 *6128 = 3064Ὠ
R2= 6128-3064 = 3064Ὠ
Thus the components values are:C= 0.047uF, R1= =R2 = 3064Ὠ
LAB:- CEII (SEM V EXTC)
Procedure
1. Mount the circuit as per design on bread
board.
2. Apply Vcc= 5V
3. Observe the output and capacitor voltage
waveforms on CRO.
4. Compare the obtained results with designed
values.
LAB:- CEII (SEM V EXTC)
Observation
Map out the time period of the output wave form
and compare it with the given one.
Parameter
Designed
Ton
Toff
LAB:- CEII (SEM V EXTC)
Observed
Results and Discussion
The waveform is observed and verified with
required condition.
LAB:- CEII (SEM V EXTC)
Questions
1. What is the working principle of astable
Multivibrator?
2. Why the name is given as astable?
LAB:- CEII (SEM V EXTC)