I got a silly question to ask.
I am quite new to electronics and these kind of stuff.
I am trying to calculate the value of resistor use for charging 4700uF cap
from 1/3 to 2/3 of the supply voltage(6 volts) I had tried to figure out how to, but I can't find the way.
Is there any equations or ways to solve this problem?
Simply saying: Any resistor may charge a capacitor from 1/3 to 2/3 of the supply voltage.
Varying the resistor value will vary the time ... and the current.
if you want to stop the charging at 2/3 of the applied volts you will need a resistive divider, e.g. 10 ohm and 20 ohm with the 20 ohm across the grounded cap
this will charge from zero to 2/3 of applied V,
Are you trying to design a long time timer ckt for a 555 by any chance ...?
The time to charge from 1/3 to 2/3 is very roughly half a time constant, which is Rcharge x C ( then divide by 2 )
"Are you trying to design a long time timer ckt for a 555 by any chance ...?"
I am working on different circuits I can do with 555 but I dont really understand the calculation for capacitor
so I searched for some information in my language but there is not much I could find so I try to search in english
but I can't find a good keyword for it
now I come up with this equation "ln(1-V1/Vs)-ln(1-V2/Vs) = t"
not sure if it works but it still work in all of my case
If you want to know the time, you must specify the resistor and the capacitor; they decide together the time constant.
If you want to know the resistance value, you must specify the time.
Now for the details. RC (product of R and C) has the dimension of time. In this story, you will notice R and C will always appear together.
During charging, the voltage increases from 0 to V (the final value) but that takes infinite time. Both charging and discharging are exponential process.
33% charging will take -RC*log(0.66) s and 66% charging will take -RC*log(0.33) s. So the time to charge is RC*0.415s to RC*1.109s.