Calculate frequency NE555 sawtooth generator

[Derekk02]

Hi,

I've build this schematic:

I have choosed the C and the R empirical. I have now about 5K resistor and a 10nF C. This give me a 10kHz frequency.

On the website where I found the schematic they use the following formula to calculate the frequency:
https://www.circuitstoday.com/saw-tooth-wave-generator-using-ne555
f = (Vcc-2.7)/(R*C*Vpp).

But when I calculate the frequency with this formula I get a whole other result: f = (12-2.7)/(5k*10nf*10) = 18,6 Hz.
Can someone explain this to me? Is there something wrong with the formula? How can I calculate the frequency?

Thanks.
Derek

 

[goldsmith]

Dear Derek
Hi
The calculation of R and C is pretty simple . see below , please , the way is the same :
https://www.edaboard.com/blog/1576/
Best Wishes
Goldsmith

 

[Derekk02]

Dear Derek
Hi
The calculation of R and C is pretty simple . see below , please , the way is the same :
https://www.edaboard.com/blog/1576/
Best Wishes
Goldsmith

Thank you for your reply. I've tried to calculate it with the calculations from the link, but I cant get the hang of it.
I'm a littble bit confused by the voltage across the zener-diode

 

[goldsmith]

Hi again .
Just consider that IE=VZ/R =Ic . i think now with that formula and this consideration you can calculate it .
Good luck
Goldsmith

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BTW : you can calculate the required IE , according to the out put voltage and then you have the value of zener diode , and you can calculate the value of R , simply , or vice versa .

 

[ayu106]

Hi Derekk, I also face the same problem. I have tried to calculate the R and C values to get 60 Hz. But I can't get that.
Have you found the way to calculate the frequency?
Thanks