Talk:RLC circuit

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Questions and comments about some images[edit]

1. What is the purpose of circuits like the ones in figures 7 and 8? Would they be used in low-pass, high-pass, notch, bandpass or some other filters?

2. I don't think figures 12 and 13 are correct. I think figure 12 should have the resistor in series with the tank and I think figure 13 should have the resistor in series with the inductor and the capacitor. I simulated a variety of combination of LRC circuits in PSpice and I don't see how the output can be where they are shown. The input matches the output and the Bode plots I get are obviously flat.

ICE77 (talk) 08:40, 17 June 2015 (UTC)

Figure 7, as explained in the text, is the equivalent circuit of a practical parallel resonator taking into account the inductor winding resistance. Figure 8, also explained in the text, is the equivalent circuit of a series resonator taking account of the capacitor dielectric loss. Resistors are not commonly deliberately inserted into filter circuits as an actual component, although Zobel networks sometimes do something similar to cvompensate for lossy components and maintain the correct input impedance.
Figure 12 is pretty much the equivalent circuit of the output of a tuned amplifier. There must, of course, be some impedance in the source for the circuit to work into – ideally a constant current source. Similarly for figure 13, which is a configuration used for wave traps, see this book for instance. I daresay you have assumed an ideal voltage source in PSpice, so it is not surprising you get flat responses.
SpinningSpark 19:43, 17 June 2015 (UTC)

Where does the term "fractional bandwidth" and symbol come from?[edit]

I don't think it's a problem using the words "fractional bandwidth" and to express that as , but giving it a mathematical symbol like seems like an ugly neologism. Shouldn't this (in addition to the photoshopped RLC circuit "photo") be removed? (talk) 01:59, 12 November 2015 (UTC)

I don't think it is very important what symbol we use as long as the article is self-consistent, but I have now changed it to per this book. Using B or BW for bandwidth is widespread and this book uses the similar for fractional bandwidth. There is no widely used symbol for fractional bandwidth; this book uses to distinguish it from absolute bandwidth and this book uses . Many authors do not define a symbol at all. SpinningSpark 09:29, 6 July 2017 (UTC)

Questions and comments about an equation[edit]

@Spinningspark: I would like to ask why the lower limit of integration of the second equation in the section "series RLC circuit" RI(t) + LdI(t)dt+∫t-∞I(τ)d(τ)= V(t) is -∞. states that "the capacitor's momentary voltage Vc(t) is equal to the initial voltage of the capacitor, plus 1/C times the integral of the capacitor's momentary current Ic(t) over time t." (see the formula in the link in the section "Capacitor's voltage") Is this conclusion correct? If so, then can I replace the integral term in this equation ∫t-∞I(τ)d(τ) with V(0)+∫t0I(τ)d(τ) since the improper integral may be undefined? Onmaditque (talk) 12:14, 1 July 2017 (UTC)

Yes, the integral from −∞ to 0 will be the initial capacitor voltage at t=0 if we assume that the capacitor had no charge when it was created. SpinningSpark 14:23, 1 July 2017 (UTC)