Topic IC 555 Timer By Prof Farhan Shaikh

Topic: IC 555 Timer By Prof. Farhan Shaikh Subject: Design with Linear Integrated Circuit Branch: ETRX Sem: V Rizvi College of Engineering Prof. Farhan Shaikh DLIC

555 timer IC pin diagram Rizvi College of Engineering Prof. Farhan Shaikh DLIC

Internal structure inside IC 555 Rizvi College of Engineering Prof. Farhan Shaikh DLIC

Internal Structure of 555 timer IC Rizvi College of Engineering Prof. Farhan Shaikh DLIC

555 TIMER AS MONOSTABLE MULTIVIBRATOR Rizvi College of Engineering Prof. Farhan Shaikh DLIC

• • • • • 1. apply a negative trigger on comparator 2’s negative terminal 2 output of c 2 will become high 3 Q bar will become high 4 Q will become low 5. Transistor acts as open circuit 6. Capacitor gets the path to charge through vcc 7. As soon as charge of the capacitor goes above 2/3 vcc, upper comparator will get higher voltage at its positive terminal 8 output of comparator 1 will go high 9 FLIPFLOP will be set 10 hence Q becomes 1 11 Q bar will go low. 12 Q will become high 13. Transistor connected to it, becomes on, acts like a short circuit 14. capacitor gets the path to discharge 15. upper comaparator won’t get its 2/3 vcc anymore 16. upper comparator’s output will go low 17. This state will remain as it is until next trigger is applied. 18. Since we have control over chnge of state from low to high but not from high to low It is called as monostable multivibrator Rizvi College of Engineering Prof. Farhan Shaikh DLIC

555 timer as ASTABLE MULTIVIBRATOR Rizvi College of Engineering Prof. Farhan Shaikh DLIC

Working 1. Assume that flipflop is set initially. 2 This will make q high and Q bar low 3 Transistor acts as short circuit 4. Capacitor gets the path to discharge towards transistor’s ground 5 This would make c 1 go low and c 2 will go high 6 Hence Qbar will go high. 7. Transistor gets open circuit, capacitor starts charginging towards vcc • 8. as voltage of capacitor reaches more than 2/3 vcc, c 1 will give high output, meaning set pin is high. That is cycle will repeat • 9. since we are not giving any trigger name is astable. • • Rizvi College of Engineering Prof. Farhan Shaikh DLIC