Capacitor charge time

[Paultergeist]

Hello!

I know how to determine the charge time required for a RC circuit, but I have doubts about how to determine the charge time for a RC circuit with another resistor connected in parallel with the capacitor.

In my case, I have a 24VDC power supply connected to a 56K resistor which is connected is series to a parallel of a 3K3 resistor and a 1µF capacitor.

How can I determine the charge time of the capacitor in this circuit? I know that the voltage in capacitor, when fully charged will be around 1.336V...

If you didn't understand the circuit:




Thank you for your help!

 

[keith1200rs]

Use Thevenins theorem. Ignore the capacitor to begin with and look at the voltage source and resistors. They are equivalent to a 1.336V source with 3.116k resistor in series. So, the CR is 3.116k with 1uF.

Keith

 

[Paultergeist]

Thanks! :-o

 

[LvW]

Paultergeist,

as another simple method imagine that the capacitor would be charged already and let it discharge.
Thus, with a shorted input voltage both resistors act in parallel - and the time constant to discharge is identical to the time constant for charging.