RC CIRCUIT Step and Pulse Response

Cuthbert Nyack

The RC circuit is shown schematically above with the alternating source replaced by a steady source. If a unit step is applied at time zero, then the capacitor voltage is given by V(C) = 1 - e-t/RC and the resistor voltage by e-t/RC. This is illustrated by the applet below. The capacitor voltage is shown in red and the resistor voltage in green. The resistor voltage also gives an indication of the current in the circuit.




If the voltage after time T is set to zero(s moved from a to b), then the resulting transient response is shown below.



For 0 t T the response is Vc = 1 - e-t/CR
For T < t the response is Vc = e-t/CR (eT/CR - 1 )
For t < T , Vc + Vr = 1 and
fot t > T , Vc + Vr = 0.
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COPYRIGHT 1996 Cuthbert A. Nyack.