EXPLANATION OF RLC PARALLEL WITH NON IDEAL INDUCTOR(having series R)

[nishanchettri]

RLC Circuit(Inductor with series Resistance):

Frequency Response:

RLC Parallel Circuit:

Frequency Response:

Question:
1. Why the difference in behavior at low Frequencies in the ideal RLC parallel circuit and the RLC parallel circuit with Series Resistance in L branch?
2. Why there is Dip in the Impedance at Resonant frequency from ideal to non ideal case seen at the frequency plot?

 

[BigBoss]

Because Inductive Reactance approaches to zero while the frequency goes down. So Voltage also approaches to zero ( near )

 

[nishanchettri]

Because Inductive Reactance approaches to zero while the frequency goes down. So Voltage also approaches to zero ( near )

But in normal RLC parallel too there is an inductor. It doesn't happen there?

 

[G4BCH]

The resistance of the ideal inductor is zero. If you pass a DC current through it the current is infinite and the voltage across it is zero.
The first circuit you show has a resistor in series with the inductor so there will be a voltage at vlrpc. Almost 1V if the current is 1A.

 

[BigBoss]

But in normal RLC parallel too there is an inductor. It doesn't happen there?

\[ X_{L}=\lim\limits_{f \to 0} 2\pi f L \rightarrow 0 \]

 

[biff44]

this might be an interesting theoretical question you are asking.
but it does not have any practical real world application! All physical components have parasitics. An inductor will have series resistance, and possibly some distributed capacitance where coils come close to a ground plane.
capacitors can have series resistance too, but more importantly there is a parallel resistance to worry about. and capacitors can have series inductance too.

An obvious example of parasitics having a big effect, if you needed a DC blocking capacitor (that passes a 2 GHz signal thru it), you would do well with a 100 pF ceramic 0603 size chip capacitor, but you would do very poorly using a 1 uf tantalum leaded capacitor.

at microwave frequencies, these tiny parasitic capacitances, inductances, and resistances can really screw up circuit operation. For instance, if you try to physically build a bandpass filter, but do not pay attention to chosing low parasitic components that have high Q factors, your bandpass filter will be:
1) centered at the wrong frequency
2) have the wrong bandwidht
3) have excess unexpected insertion loss in the passband
4) have poor out of band rejection

a good exercise is to go to a website like Digikey, choose actual surface mount capacitors and inductors, carefully look over the data sheets to see these capacitances, and design the circuit with a good model of them. If you can not find useful info on the data sheet for a component, you either measure the components one-at-a-time to learn the parasitics....or use a service like Modelithics provides where they already measured commonly used chip components and have accurate models to use.