An RC charging circuit has a series R and C connected to a battery of EMF potential VCC. The battery voltage causes a current i to flow through the circuit. The current is not constant because the battery continues to charge the capacitor, and the resulting charge lowers the effective EMF of the circuit leading to a fall in the current flowing through the circuit. It is possible to determine the current as well as the voltages at various points of an RC circuit using integral calculus. However, if you just want to quickly calculate the various parameters, then here is the online calculator.
We shall follow the following circuit. There is an EMF Vcc across the RC series circuit. The voltage across the capacitor changes from Vi to Vf in time t. The equation is: Vf = VCC + (Vi - VCC)e-t/RC
Usually Vi is 0v, but in some switching circuits like an astable multivibrator, the charging starts from an initial negative voltage. So I have given a general solution that includes Vi as a parameter.
Calculate t when VCC, R, C, Vf and Vi are known
Use this form to find the time taken by the voltage to reach Vf.
| VCC: | V | |
| R: | kΩ | |
| C: | μF | |
| Vi: | V | |
| Vf: | V | |
Calculate Vf when VCC, R, C, t and Vi are known
Use this form to find the value of Vf after a time t.
| VCC: | V | |
| R: | kΩ | |
| C: | μF | |
| Vi: | V | |
| t: | milliseconds | |
Calculate R when VCC, Vf, C, t and Vi are known
Use this form to find the value of R that will take the voltage to Vf after a time t.
| VCC: | V | |
| C: | μF | |
| Vi: | V | |
| Vf: | V | |
| t: | milliseconds | |
Calculate C when VCC, Vf, R, t and Vi are known
Use this form to find the value of C that will take the voltage to Vf after a time t.
| VCC: | V | |
| R: | kΩ | |
| Vi: | V | |
| Vf: | V | |
| t: | milliseconds | |
Capacitor Discharging Calculator?
Click here for capacitor discharging circuit calculator: Capacitor Discharging (Online Calculator Free)