Transient Response of RC circuits

Objective

Plot the voltage across a capacitor, when it is charged by applying a voltage step through a resistor. Calculate the value of the capacitance from the graph.

_images/RCtransient.svg _images/RCtransient.png

Procedure

  • From \emphElectrical , select \emphRCTransientresponse
  • Click on 0->5V STEP and 5->0V step Buttons to plot the graphs
  • Adjust the horizontal scale, if required, and repeat.
  • Calculate RC time constant.

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 U(t) = U_0 \times e^{− t/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) \times t.