# Combination of RC circuit in DC and AC?

Discussion in 'General Electronics Chat' started by vead, Aug 12, 2016.

1. ### vead Thread Starter Well-Known Member

Nov 24, 2011
621
8
Hello
I am trying to understand the basic concepts of RC combination in AC and DC supply. I draw below circuit for basic understanding
I did Google search and I found that all combination of RC circuit are the filter circuit, That is used in AC and DC circuit. Combination of RC circuit is use to pass or block frequency in AC. And the capacitor with parallel resistor used in DC power supplies.
I just need to understand where and which type of combination is used in circuit

2. ### CEJones New Member

Feb 12, 2016
13
3
AC and DC combinations are all the same. The way this works is you convert the impact using a la pace transform. For a capacitor we know i=c (dv/dt). For a resistor v=i*r and for an inductor v=L(di/dt). Laplace changes derivatives into s (j*omega in terms of frequency) and integrals to 1/s.
Using this the resistor is v/I. We want the same relation for the others.
Inductors L=s*v/I
Capacitors C=v/I * 1/s
Based on this inductors combine similarly to resistors and capacitors combine inversely (indicated by the 1/s).
This is where the theory comes from and so it is always possible to combine your filters as phasers (ac resistors) and treat everything as DC. If you have the two put together you can treat the two cases separately and due to superposition the combine result is the sum of both solutions.
Hope this helps. I'm sure it was probably more than you were looking for.