>> How does one calculate the charge time of an RC circuit?  I
>> know the voltage, the capacitor value and the resistor value
>> of course.  I am sure it does differ with the temperature also,
>> but for now I am assuming room temperature.  It would be nice
>> to know how the temperature effects (by
>> formula) the charge time also.

Mike said:

Vc(t) = Vo e^(-t/RC )

Where:
Vc(t) is the voltage across the capacitor at time t
Vo is the voltage applied across the resistor/capacitor.
R resistance in Ohms
C capacitance in Farads.
_______________

RM sez:

Also, just in case it's not obvious

    where e = e :-)

      e ~= 2.718282
           = base of natural logarithms

Also, rearranging:

t = -RC * ln(Vc/V0)

______

Also the "time constant" given by the simple product

    T = R * C

is the time taken to charge to 0.632 of the full value.

Exercise for the student:

    Derive the above value using the formula supplied by Mike.

___________________________________

Worked examples

        http://www.tpub.com/neets/book2/3d.htm








            Russell McMahon

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