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Help me solve 555 timer equations

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Fluzer

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Hi everybody.
I have registered hoping to find the answer to my doubts. But far from learning the meaning of life, I only need one simple (or not xD) thing.
I'm studying 555 timer, I know its equations and its two modes, astable and monostable, but the answer is. How can I deduct its equations? Where do they come from? I cannot find the answer. I'd thank you could lend me a hand xD
The equations I am talking about are:

Monostable
Th = 1,1 Ra*C


Astable
t1 = ln2 *(Ra + Rb)*C
t2 = ln2*(Rb)*C
 

555 equations

Hi,

You can just look at the block diagram of 555 timer
then you will get an idea.

you can get BD from internet

Regards,

Analayout.
 

555 timer equation

Hi,
if you know the equations of carging, and discharging a capacitor you will get the equations you mentioned.

the upper and lower limits of the capacitor voltages are 2/3 Vcc, and 1/3 Vcc (from NE555 datasheet).

the equation of discharging a capacitor is Vc(t) =2/3 Vcc * exp-t/Rc substitute Tlow for t and 1/3 Vcc for Vc(t) this will determine Tlow.
As for T high the following equation applies

Vc(t) = (Vc final _ Vc initial) (1- exp-t/rc) + Vc initial

substitute Vc final =Vcc ( the capacitor will try to charge to a final valur of Vcc but the comparator will allow it to charge t to 2/3 Vcc only and will change the output state ), Vc initial = 1/3 Vcc, and t=Thigh
If you do so you will get the equqtions you mentioned.
If I can help you more let me know
regards,
M.Mokhtar
 

equations for 555 timer

for monostable vibrator mode
charging tome constant = ln2 R * C
and ideally discharging time constant is zero
as C charges gradually
Vc increases hence when trigger input is applied the output changes from active low quasi stable state to stable state
hence
duration of QSS = ln2 RC

Added after 1 minutes:

for astable vibrator circuit M.Mokhtar sir has already mentioned

regards teja
 

555 astable equation

The following might help:
cng.ateneo.edu/cng/wyu/works/papers/555.pdf
Regards,
Kral
 

555 circuit equations

The derivation is given in text book "Linear Integrated Circuits" by D. Roy Choudhary. This is an Indian text book. I don't know whether it is available there.

Hope you find that,

SUjO
 

555 timer th formula

Take a look at:
**broken link removed**

There are examples and circuits for all forms.
<als>
 

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