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# Ee2 chapter16 astable_operation

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### Ee2 chapter16 astable_operation

1. 1. IT2001PAEngineering Essentials (2/2)Chapter 16 - Astable Operation of the 555IC Timer Lecturer Namelecturer_email@ite.edu.sg Nov 20, 2012Contact Number
2. 2. Chapter 16 - Astable Operation of the 555 IC TimerLesson ObjectivesUpon completion of this topic, you should be able to: Students should be able to calculate the time delay/frequency of a 555 timer circuit with given formula. IT2001PA Engineering Essentials (2/2) 2
3. 3. Chapter 16 - Astable Operation of the 555 IC TimerSpecific Objectives Students should be able to :  Draw the circuit of an astable multivibrator using IC 555.  Calculate the mark and space timing of the astable multivibrator.  Calculate the oscillator frequency using the formula : Fosc = 1.44 /(R1 + 2R2) C IT2001PA Engineering Essentials (2/2)
4. 4. Chapter 16 - Astable Operation of the 555 IC TimerThe Astable Multivibrator  It is a free-running oscillator.  It outputs a rectangular wave and does not require any trigger input. • Application as oscillators, square-wave enerators etc. Input Circuit Output Astable None Multivibrator IT2001PA Engineering Essentials (2/2) 4
5. 5. Chapter 16 - Astable Operation of the 555 IC Timer 555 as Astable Multivibrator +V Output R1 Vcc 8 7 3 Output t1 t2 R2 555 t1 = 0.693 (R1 + R2 ) C 6 5 t2 = 0.693 R2C 2 1 0.01µF C 1.44 fOSC = 0.693 (R1 + R2 ) C IT2001PA Engineering Essentials (2/2) 5
6. 6. Chapter 16 - Astable Operation of the 555 IC TimerExample : To calculate the Mark , Space and the frequency of oscillations of the output waveform. Given that C = 0.001µf, R1 = 4 KΩ and R2 = 100KΩ.Solution : Mark, t1 = 0.693 (R1 + R2)C Output = 0.693 (4 KΩ + 100KΩ) 0.001µf Vcc = 0.693 (4 000 + 100 000) 0.001 x 10-6 = 0.000 0721s = 72.1µs 0 Space, t2 = 0.693 R2C t1 t2 = 0.693 (100KΩ) 0.001µf tosc = 0.693 (100 000) 0.001 x 10-6 = 0.000 0693s = 69.3µs 1.44 Frequency, fosc = (R1 + 2)C 2R 1.44 = (4k + 200 k ) 0.001 x 10-6 = 7059Hz IT2001PA Engineering Essentials (2/2) 6
7. 7. Chapter 16 - Astable Operation of the 555 IC TimerNext Lesson IT2001PA Engineering Essentials (2/2) 7