The document presents an overview of the 555 timer, an integrated circuit designed for various timing and pulse generation applications. It includes details on its pin configuration, types (monostable, astable, bistable multivibrators), functioning, and related formulas. Applications of these configurations include frequency dividers, pulse stretchers, square-wave oscillators, and more.

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