555 TIMER 1. CONTENTS :-INTRODUCTION PIN DIAGRAM TYPES WORKING 2. INTRODUCTION 3. PIN DIAGRAM 4. PIN FUNCTIONING 5. CIRCUIT DIAGRAM 6. TYPES :-1) MONOSTABLE MULTIVAIBRATOR 2) ASTABLE MULTIVAIBRATOR 3) BISTABLE MULTIVAIBRATOR 7. FOMULAS 8. APPLICATIONS OF MONOSTABLE MULTIVIBRATOR 1) FREQUENCY DIVIDER 2) PULSE STRETCHER 9. APPLICATIONS OF ASTABLE MULTIVIBRATOR 1) SQUARE – WAVE OSCILLATOR 2) FREE- RUNNING RAM GENERATOR 10. THANK YOU

1. GOVERNMENT ENGINEERING
COLLEGE, GANDHINAGAR
Submitted by:-
Tanish Gupta{150130117029}

2. ANALOG SIGNAL PROCESSING

3. TOPIC :-
555
TIMER

4. CONTENTS :-
• INTRODUCTION
• PIN DIAGRAM
• TYPES
• WORKING

5. INTRODUCTION
• 555 timer is and integrated circuit.
• It is used in variety of timer ,pulse
generator ,oscillator .
• It is used to provide delays in
oscillator circuit .
• It was designed in 1971 by hans r.
camenzind .

6. INTRODUCTION
• NE-555 is used at
commercial range of 0˚c to
70˚c .
• SE-555 is used at military
purpose , it range of -55˚c
to 125˚c .

7. PIN DIAGRAM
• PIN1 – GROUND
• PIN2 – TIGEER
• PIN3 – OUTPUT
• PIN4 – RESET
• PIN5 – CONTROL
• PIN6 – THRESHOLD
• PIN7 – DISCHARGE
• PIN8 – SUPPLY +Vcc

8. PIN FUNCTIONING
• pin1 :- Ground , the ground pin connects the
555 timer to the negative (0v) supply rail .
• pin2 :- Trigger ,the negative input to comparator
no. 1. a negative pulse on this pin “sets” the
internal flip-flop when the voltage drops below
1/3 vcc causing the output to switch from a
“low” to a “high” state .
• pin3 :- Output , the output pin can drive any
till circuit and is capable of sourcing or sinking
up to 200ma of current at an output voltage
equal to approximately vcc – 1.5v so small
speaker , leds or motors can be connected directly
to the output .

9. • pin4 :- Reset , this pin is used to “reset” the internal
flip-flop controlling the state of the output ,pin3 . this
is an active-low input and is generally connected to a
logic “1” level when not used to prevent any unwanted
resetting of the output .
• pin5 :- Control voltage , this pin controls the timings
of the 555 by overriding the 2/3 vcc level of the
voltage divider network . by applying a voltage to this
pin the width of the output signal can be varied
independently of the rc timing network . when not used
it is connected to ground via a 10nf capacitor to
eliminate any noise .
• pin6 :- Threshold , the positve input of comparater no.
2 . this pin is used to reset the flip-flop when the
voltage applied to it exceeds 2/3 vcc causing the
output to switch from “high” to “low” state . this pin
connects directly to the rc timing circuit .

10. • pin7 :- Discharge , the discharge pin
isconnected directly to the collector of an
internal npn transistor which is used to
“discharge” the timing capacitor to ground
when the output at pin 3 switches “low” .
• pin8 :- Supply +vcc , this is he power supply
pin and for general purpose ttl 555 timers is
between 4.5v and 15v .

11. CIRCUIT DIAGRAM :-

12. TYPES :-
• 1) MONOSTABLE
MULTIVAIBRATOR
• 2) ASTABLE
MULTIVAIBRATOR
• 3) BISTABLE
MULTIVAIBRATOR

13. 1) MONOSTABLE
MULTIVAIBRATOR

14. WORKING :-
• According to the fig. , initially when the
output is low , that is , circuit is in the stable
state , transistor Q1 is on and the capacitor C
is shorted out to ground . However , upon
application of a negative trigger pulse to pin 2
, transistor Q1 is turned off , which releases
the short circuit the external capacitor C
and driver the output is high .
• The capacitor C now starts charging up toward
Vcc through Ra.

15. • However , when the voltage across the
capacitor equal 2/3 Vcc , comparator 1’s
output switches from low to high ,which in
turn drives the output to its low state via the
output of the flip-flop .
• At the same time , the output of the flip-flop
turns transistor Q1 on and hence capacitor C
rapidly discharges through the transistor .
• The output of the monostable remains low
until a trigger pulse is again applied . The
cycle repeats .
• The time during which the output remains
high is given by Tp = 1.1RC seconds .

16. 2) Astable Multivibrator

17. WORKING :-
• Fig. shows the 555 timer is connected as an astable
multivibrator . Initially , when the output is high
, capacitor C starts charging towards Vcc through
Ra and Rb .
• However , as soon as voltage across the capacitor
equal 2/3 Vcc , comparator 1 triggers the flip-
flop , and the output switches low .
• Now capacitor C starts discharge through Rb and
transistor Q1 .
• When the voltage across C equals 1/3 Vcc ,
comparator 2’s output triggers the flip-flop and the
output goes high .
• The cycle repeats .

18. FOMULAS :-
• CHARING TIME
Tc = 0.69(Ra +Rb)C
• DISCHARGING TIME
Td = 0.69(Rb)C
• TOTAL PERIOD
T = Tc +Td
• FREQUENCY
f = 1/T = 1.45/(Ra + 2Rb)C
• DUTY CYCLE
D = Tc/T = Ra + Rb/Ra + 2Rb

19. 3) BISTABLE
MULTIVIBRATOR

20. APPLICATIONS OF
MONOSTABLE
MULTIVIBRATOR :-
•1) FREQUENCY
DIVIDER
•2) PULSE
STRETCHER

21. A) FREQUENCY
DIVIDER B) PULSE STRETCHER

22. APPLICATIONS OF ASTABLE
MULTIVIBRATOR
•1) SQUARE – WAVE
OSCILLATOR
•2) FREE- RUNNING
RAM GENERATOR

23. A) SQUARE –WAVE
OSCILLATOR
B) FREE- RUNNING RAMP
GENERATOR

24. THANK
YOU