# working with ic555

Posted on Feb 6, 2014

As we know its on chip multivibrator means with IC555 one can design astable, monostable, bistable multivibrators. Its main applications are to generate timings, clock waveform, generate synchronizing signals, square wave oscillator and many more. So here we are going to discuss some of the applications of IC555. But before that I will start with the basic theory. Here I shall

not discuss the internal block diagram and theory of IC555 that how does it work in astable or monostable operation as everybody is already familiar with that. But here there is a practical approach given to explain how to design different applications of the chip. Here frequency and duty cycle are the design parameters and we have to find out three unknowns R1, R2 & C. For given values of design parameters, we have to find out these three unknown. Here we have to assume the value of C, as from two equation we can not find three unknown. Let us assume C=0. 01 microF. Substituting this value into first equation From the equations (3) and (4) we can find out R1 = 720 ohm and R2 = 1. 44K. The nearest practical values will be 715 ohm and 1. 43K. Substituting these values back into the design equations, we shall get freq = 40 KHz (nearly equal to) and duty cycle = 60%. If we use potentiometer of 4. 7K instead of fixed value of R2 then we can set the exact 40 KHz freq. by tuning value of R2. Now it is not possible to design an astable multivibrator with exact 50% duty cycle using these equations and above circuit. If you want to design an astable multivibrator for exact 50% duty cycle then we have to do slight modification in above circuit by connecting one diode across resistor R2. Here by assuming value of capacitor one can easily find the value of resistor. Duty cycle will be always 50%. For above values of frequency (40 KHz)...

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