NE555 astable frquency

1. NE555 astable frquency

Hi,
How do I calculate the frequency of this circuit?

Thanks.

2. Re: NE555 astable frquency

For a rough estimation, assume RV1 in center position, ignore diode voltage drop, use formula for astable operation in data sheet (R1=1k, R2=5k).

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3. Re: NE555 astable frquency

Originally Posted by FvM
For a rough estimation, assume RV1 in center position, ignore diode voltage drop, use formula for astable operation in data sheet (R1=1k, R2=5k).
Why is R2=5k?

4. Re: NE555 astable frquency

RV1 center position, 10k/2 is effective R2 value (ignoring the diode voltage drop).

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5. Re: NE555 astable frquency

Originally Posted by FvM
RV1 center position, 10k/2 is effective R2 value (ignoring the diode voltage drop).
So the frequency is : f = 1.44 / ((R1 + 2*R2)*c) = 13KHz ?

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6. Re: NE555 astable frquency

1/((R2+k*Rv1)+(1-k)*Rv1)

where 'k' as per figure is 0.41

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Originally Posted by srizbf

1/((R2+k*Rv1)+(1-k)*Rv1)

where 'k' as per figure is 0.41

7. Re: NE555 astable frquency

Originally Posted by srizbf

1/((R2+k*Rv1)+(1-k)*Rv1)

where 'k' as per figure is 0.41
But by using your equation the frequency will be : 9 * 10^(-5) Hz !!

8. Re: NE555 astable frquency

Originally Posted by Blue10
But by using your equation the frequency will be : 9 * 10^(-5) Hz !!
again a typo.

the term 'c' is left out in denominator.

so the freq is of the form:

1.44/((R2+kRv1)+(1-k)Rv1)C2

9. Re: NE555 astable frquency

Since the frequency of the 555 doesn't vary much with the setting of the duty-cycle pot, the value you get using 1/2 the pot resistance should be good enough for a reasonable estimate of the frequency.

10. Re: NE555 astable frquency

@Blue10
where did you find that circuit?

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11. Re: NE555 astable frquency

That circuit is all over the internet.