Transient Response of RC circuits

Objective

Plot the voltage across a capacitor, when it is charged by applying a voltage step through a resistor. Extract the value of RC from the graph by curve fitting.

Procedure

schematics/RCtransient.svg pics/RCtransient-screen.png

Discussion

Applying a 0 to 5V step makes the voltage across the capacitor to rise exponentially as shown in the figure. By fitting the discharge curve with V(t) = V0 × et ⁄ RC, we can extract the RC time constant and find the values of capacitance from it.

The voltage across a capacitor is exponential only when it is charged trough a linear element, a resistor for example. When charged from a constant current source, the voltage shows linear increase, because Q = It = CV , and voltage increases linearly with time as V = (I ⁄ C) × t.

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