Need equation to calculate frequency of 555

[polashd]

dear all

I need the equation to calculate frequency of timer 555 for the schematic attached.
can any one please provide me the formula for this diagram.

 

[Spudboy488]

It's usually in the datasheet.

https://www.onsemi.com/pub/Collateral/LM555-D.pdf

https://www.ti.com/general/docs/sup...Id=10&gotoUrl=http://www.ti.com/lit/gpn/lm555

 

[gophert]

Not for the circuit he drew! I've never seen that version of a PWM circuit with a 555.

 

[polashd]

It's usually in the datasheet.

As I mentioned, the equation should be applicable for the diagram I attached.
I use this diagram to vary duty% without affecting frequency.

 

[polashd]

Not for the circuit he drew! I've never seen that version of a PWM circuit with a 555.

Thanks for understanding this, which I mentioned in both lines of my post.

In most schematics if you change one (frequency / duty%) the other gets affected (as far I understand (which is very little)).

 

[Nigel Goodwin]

As I mentioned, the equation should be applicable for the diagram I attached.
I use this diagram to vary duty% without affecting frequency.

To do that you have to alter two resistors at the same time (R2/R3), hence the two separate timing resistors and diodes so that one charges and the other discharges. So you would probably need to calculate the timing of each resistor separately, and combine them to give the combined frequency. Presumably the diodes will affect the actual result to some degree?, but calculations are fairly inaccurate anyway.

 

[polashd]

To do that you have to alter two resistors at the same time (R2/R3),

In actual circuit there is a veritable resistor in place of R2 & R3. I showed here separately for the equation to be easily written.