# Impedance in pulsed DC circuits???

Discussion in 'General Electronics Chat' started by electronice123, Jul 23, 2010.

1. ### electronice123 Thread Starter Senior Member

Oct 10, 2008
304
0
I have been wondering lately about impedance in pulsed DC circuits...

Since the circuit is a pulsed DC circuit how do you calculate impedance in say a circuit with a 100 Ohms resistance and a 50 ohm inductive reactance...

Do you just add the two together to get Z=150 Ohms?

2. ### debjit625 Well-Known Member

Apr 17, 2010
790
186
If they are in series yes we add it,and for the pulsed DC (non-sinusoidal) its a mixed frequency so the circuit will behave like we have given it different frequency voltage at once.Its like we have connected many AC power source in a series form and each source have different frequency.

So the calculation is quite different you can use superposition theorem.

Good Luck

3. ### timrobbins Active Member

Aug 29, 2009
318
16
If the components are ideal then the steady state 'impedance' is just 100R, because you have no time varying (ie. frequency related) voltage component for the inductance to contribute an effective 'impedance' to. The series RL impedance is always there, and exhibits itself as the time constant of the transient waveform between stepped steady state DC levels - as described by the standard exponential equation characteristic.

As debjit indicated, a pulse has a characteristic frequency spectrum, so if you don't have an ideal stepped dc waveform then the standard exponential equation characteristic is not valid and you need to collate the response from all the frequency components of the driving waveform. And you need to use load impedance values that relate to those frequencies (ie. non-ideal loads). The joy of being able to do a transient sim!

Ciao, Tim