# 555 timer astable multivibrator

1. ## 555 timer astable multivibrator

In the following astable multivibrator circuit,

in some books, it is mentioned that the duty cycle id

d=( R1+R2)/(R1+2*R2)

in some other books, it is mentioned

d= R2/(R1+2*R2)

which is correct? which one should i use if i want to design a circuit of particular duty cycle ?

please tell me whether duty cycle is Ton/(Ton+Toff) or Toff/(Ton+Toff)

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3. ## Re: 555 timer astable multivibrator

duty cycle is Ton/(Ton+Toff)

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4. ## Re: 555 timer astable multivibrator

Originally Posted by ckshivaram
i can't understand still sir.. please explain me ..

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5. ## Re: 555 timer astable multivibrator

555 Calculator

Also check 555 and 556 Timer Circuits

Alex

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6. ## Re: 555 timer astable multivibrator

which is correct? which one should i use if i want to design a circuit of particular duty cycle ?
please tell me whether duty cycle is Ton/(Ton+Toff) or Toff/(Ton+Toff)
I think, it's your choice. That's also the reason, why both expressions for d exist.

In my opinion, you would define high output as "on" and duty cycle as Ton/(Ton+Toff).
In this case, the first expression applies: d=( R1+R2)/(R1+2*R2)

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7. ## Re: 555 timer astable multivibrator

Originally Posted by electroboy
please tell me whether duty cycle is Ton/(Ton+Toff) or Toff/(Ton+Toff)
Normally when we say that the duty cycle is 10% we mean then the output is on for 10% of the period time so I think you should use Ton/(Ton+Toff)

Alex

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8. ## Re: 555 timer astable multivibrator

Ton/Ton+Toff

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9. ## Re: 555 timer astable multivibrator

duty cycle is ton/(ton+toff)

http://teeblog.blog.com/archives/66/#as Read this for calculations and basic theory

10. ## Re: 555 timer astable multivibrator

you can also try this link for understanding 555 ic as a-stable multivibrator

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