Question about voltage of series RLC circuit in resonace

[lordsathish]

Hi.... Usually in a series RLC circuit in resonance... the voltage across the inductor and that across the capacitor are opposite to each other and is it that it might be more than the total applied across the entire RLC circuit...if so how could the voltage across the components in series is higher than the applied voltage...

 

[A.Anand Srinivasan]

Re: RLC in resonace

in series RLC circuit the voltage across the RLC components is equal to that of the supply.... The L and C components have voltage in opposite and hence the difference only occurs and the remaining voltage part is taken care by the Resistor....


Here you have to keep in mind that using a dc supply is useless.. here only a ac supply is used and hence the instantaneous current varies to make the voltage across RLC equal to supply voltage....

 

[abhikohli]

RLC in resonace

@Satish Frm what I understand you want to know how in RLC ckt at any time voltage across any element can be greater than applied voltage ? (BTW this can happen in many ckts, in just a L also) The reason is somewhat same as in case of transformer. Remember this can't happen in a steady state current (Uninterupted DC) this happens when there is change in flux which induces voltage in iinductive element. (This is just a pointer to remind things.)

 

[vivek_bahire]

Re: RLC in resonace

In AC circuit KVL is not valid, which is good only for DC ckt.

In DC ckt the voltage across the loop is zero and in AC the total phase angle is zero.

 

[zeeshanzia84]

Re: RLC in resonace

In AC circuit KVL is not valid, which is good only for DC ckt.

That's completely wrong!

KVL is always valid. In case of AC voltages, KVL has to be applied on the instantaneous voltages. At any instant, the algebraic sum of voltages in the loop is equal to zero.

 

[Fahmy]

RLC in resonace

I agree with zeeshanzia84.
The principle that you could always trust is the energy conservation principle.You can not ever obtain output power greater than the total input power .
But when you talk about votages or current you can get output voltage/current greater than the input and there is many examples for that.

 

[abhikohli]

RLC in resonace

Yes, I too agree with zeeshanzia84 as well as Fahmy Its jst that in case of AC we have different V/I values (for theory) we need to b carefull as to which eq which V/I value needs to be applied. (Instantanious, RMS etc)

 

[aledaniel]

Re: RLC in resonace

Well, here is a missconcept betwen power and enegy. We should remember that power is dE/dt so, what is conserved is the energy provided by the power source across the time (well..., if we dismiss joule effect loss). This enery can be integrated by the L or C components (in the first case it takes the form of electromgnetic field and in the second on q on the capacitor plates), so if a circuit switches the resistence in the L or C path, then that energy can be drain in a faster manner wich means HIGHER instant power and of course higher V or I.

 

[Fahmy]

RLC in resonace

I agree with aledaniel .
One thing I remembered. what lordsathish said is right for zero-order or first order systems only . But for second or higher order systems (as ciruits containing both L and C) the transfer function of the system exhibts what is called peaking which means that the output could be larger than the input.

 

[The Joy of Electronics]

Re: RLC in resonace

Hi...

I've explained a similar problem here:

 

[Kral]

Re: RLC in resonace

lordsathish,
It is true that the voltage across either reactive element can be greater than the applied voltage. For a series resonant circuit, the capacitive reactance exactly cancels the inductive reactance (they are 90 degrees out of phase with each other) for a net reactance of zero. The current, therfore is equal to Vin/R, where Vin is the applied sinusoidal voltage. The magnitude of the voltage is, therefore equal to the current times the reactance. If R = 0, then the current is infinite, and the voltage across each reactive element is infinite. Of course, this situation never happens in the real world.
Regards,
Kral

 

[satyasri]

RLC in resonace

here some amplification is going to take place the output is Q times the applied voltage.

 

[Fahmy]

Re: RLC in resonace

lordsathish,
It is true that the voltage across either reactive element can be greater than the applied voltage. For a series resonant circuit, the capacitive reactance exactly cancels the inductive reactance (they are 90 degrees out of phase with each other) for a net reactance of zero. The current, therfore is equal to Vin/R, where Vin is the applied sinusoidal voltage. The magnitude of the voltage is, therefore equal to the current times the reactance. If R = 0, then the current is infinite, and the voltage across each reactive element is infinite. Of course, this situation never happens in the real world.
Regards,
Kral

I think they are 180 degrees from each other.