# FREQUENCY CALCULATION 3525

#### MATT838383

Joined Jul 31, 2019
144
Hello everybody i am trying to set the frequency of a 3525 with this formula 1/(1,10^-9*(0,7*15000+3*22))=94643HZ
where ct =µf
rt=ohms
my results=-1,05!
thank you for helping me!

#### ronsimpson

Joined Oct 7, 2019
2,261
Your number is close to -1 so there must be at least 2 problems. Should be positive and should be a large number.
"^-9" I think you are not doing that right. 1.10^-9 is a very small number.
Where did you find the formula? What is a 3525?

#### Dodgydave

Joined Jun 22, 2012
10,395
I get 94.643Khz.

15000* 0.7= 10500
+66 = 10566
* 1exp-9 = 1.05exp-5
1/ 1.05exp-5 = 94643..

#### MATT838383

Joined Jul 31, 2019
144
ronsimpson: yes a SG3525!

#### MATT838383

Joined Jul 31, 2019
144
hello dodgydave and thankyou for this formula!
best regards

#### Irving

Joined Jan 30, 2016
3,002
this formula 1/(1,10^-9*(0,7*15000+3*22))=94643HZ
That's not a formula, its a numerical expression. I get 86039Hz if you take 1.1E-9 for the first element in bold, though I can see it could be misread as 1 x 10E-9.. What was your value for $$C_t$$?

The formula is:
$$f(Hz) = 1/C_t (0.7R_t + 3R_d)$$, where $$R_t$$ and $$R_d$$are in ohms and $$C_t$$ in F

With $$R_t$$ and $$R_d$$ in ohms and $$C_t$$ in uF the result is in MHz

#### MATT838383

Joined Jul 31, 2019
144
Hello irving sorry i am late! the value for ct is 1NF
so: 1/0,001*(0.7*15000+3*22)=105660

#### Irving

Joined Jan 30, 2016
3,002
No, you must get the top & bottom right, its:

$$f(MHz)=1/C_t(0.7R_t+3R_d)$$, where $$R_t$$ and $$R_d$$ are in ohms and $$C_t$$ in uF NOT

$$f(MHz) = 1/C_t . (0.7R_t + 3R_d)$$

f = 1/( 0.001 * (0.7 * 15000 + 3 * 22)) = 0.0946431MHz = 94.64kHz

NOT

f = 1/(0.001) * (0.7*15000 + 3 * 22) = 10566000 ???