555 Timer integrated circuit and its applications

A brief description on integrated circuit 555 timer with its applications and states in which it works !

1. 555 TIMER IC MAYANK RAJ SINGH

2. INTRODUCTION The 555 IC was designed in 1971 by Hans Camenzind under contract to SigNetics Corporation. Basically, 555 timer is a highly stable circuit used to generate time delays, or Oscillations. A single 555 timer can provide time delay ranging from microseconds to hours. It operates from a wide range of  power supplies ranging from + 5 Volts to + 18 Volts supply voltage.

3. Pin Configuration The function of each pin of the IC is given below – Pin–1:   Ground Pin–2:   Trigger Pin–3:   Output Pin–4:   Reset Pin–5:   Control Voltage Pin–6:   Threshold Pin–7:   Discharge Pin–8:   Vcc

4. Functional diagram of 555 timer + - Threshold ( 2/3) Vcc R Threshold > (2/ 3) Vcc => R=logic ‘1’ Threshold < (2/3) Vcc => R=logic ‘0’ + - ( 1 /3) Vcc Trigger S Trigger <(1/ 3) Vcc => S=logic ‘1’ Trigger > (1/ 3) Vcc => S=logic ‘0’

5. Modes of Operation 555 IC Timer applications can be classified into two main categories: Monostable Multivibrators : Producing a single pulse when triggered. Astable Multivibrators : Producing a square wave.

6. 1. Monostable Multivibrator Monostable multivibrator is often called as one-shot multivibrator .

7. 1 3 +V CC 7 6 2 8 One-shot operation R C 1/3 V CC The input trigger resets the flip-flop and C then charges until the upper comparator trips and sets the flip-flop. R S input trigger output pulse Discharge transistor Q   Q Inverter

8. + V CC 555 4 8 7 6 1 3 2 R C t = 1.1 RC Output pulse Trigger 1/3 V CC The external components determine the output pulse width.

9. 2 . Astable Multivibrator Astable multivibrators are also known as  Free-running Multivibrator . Astable do not need trigger pulse for external to change the output. The period for LOW and HIGH can be calculated based on resistor and capacitor value that connected at outside of timer. C charges through R A + R B and discharges through R B .

10. 1 3 +V CC 7 6 2 8 Free-running or astable operation R B C R A R S C charges through R A + R B and discharges through R B . Inverter Q   output

11. Applications Schmitt trigger PPM PWM Linear Ramp generator

12. Conclusion Hence 555 IC timer can produce very accurate and stable time delays, from microseconds to hours. It can be used with supply voltage varying from 5 to 18 V. Timer can be used in monostable mode of operation or astable mode of operation. Its various applications include waveform generator, missing pulse detector, frequency divider, pulse width modulator, burglar alarm, FSK generator, ramp generator, pulse position modulator etc.