# Currents in RLC circuit

#### neptunemassif

Joined Apr 30, 2004
1
HOMEWORK DILEMMA
I'm a beginner so be gentle.
Attached is an image of a circuit I'm trying to figure out - no need to analyze any values, but I'm simply trying to tell what kind of current (AC or DC) runs in each component.

More importantly, HOW on earth can one tell if the current is AC or DC just by looking at the circuit, without regard to the values of the components?

I have a basic understanding of dc and ac circuit analysis, but kind of shaky in the whole series & parallel RLC circuuit area.

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#### Battousai

Joined Nov 14, 2003
141
There is only one voltage/current source in this circuit and it is an AC voltage source. Hence all the currents and voltages must be AC signals.

If you have DC supply voltages/currents then you will have DC signals. If you have AC supplies, you will have AC signals. And if you have both, then you'll have both types of signals.

The technique to use when analyzing a circuit is superposition. That is, analyze all the DC currents/voltages first, and then analyze the AC signals seperatley by themselves.

#### Mjollnir

Joined Apr 22, 2004
27
well convert everything in that circuit to phasors and impedances

#### beenthere

Joined Apr 20, 2004
15,819
Hi,

You do have a DC source and path. V1 will source current through L1 and R1. All other paths are through capacitors, which are renowned for the ability to block DC.

The 1k resistor will hold your max DC current to 12 mills. The choke effect of the coil L1 will doubtless knock off a bit, but very little.

Problems like this always wierd me out. Nobody designs crap like this. Of course, figuring out how a "real" circuit was supposed to work after several components are reduced to charcoal can be a bit tedious, too.

#### nktvnvn

Joined May 21, 2004
2
Hi everyone
I am a total novice. So please pardon me if my questions seem silly to ask.

What is the condition of resonance? The inductive reactance = the resistive reactance? Or is the circuit in resonance when the current reaches its maximum value?

I'm trying to solve a problem that asks "Find a formula for the resonance frequency for the circuit C--(R // L)." and don't know where to begin.

Thanks for your help.

#### nktvnvn

Joined May 21, 2004
2
Thanks for pointing out. I've checked the link, but am still not clear. I saw all SPICE analyses but no general formula for the resonance frequency. My case is C--(L//R), which is not included in the link.