555 Timer (detailed presentation)

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. I t is used in variety of timer ,pulse generator ,oscillator . I t is used to provide delays in oscillator circuit . I t 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 :- G round , 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 :- O utput , 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 :- R eset , 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 :- C ontrol 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 :- T hreshold , 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 :- S upply + 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 T p = 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