BOOK_CONTENT
From Network Analysis and Circuits

12.3 PHASOR DIAGRAM OF SERIES RLC CIRCUIT

The nature of the phasor diagram of a series RLC circuit depends on the
frequency f of the applied signal in relation to the frequency of resonance f0.
Three different cases may be considered:

    (i) f = fr,     (ii) f < fr, and     (iii) f > fr.

with f = f0, the reactance XL of inductor L equals the reactance
of capacitor C.

The circuit is then purely resistive and the voltage V across the circuit is
in phase with the current I. The phasor diagram for the series RLC circuit
of Figure 12.4 for the series resonance condition is shown in Figure 12.4(a).


   (a ) f = fr                  (b) f < fr               (c) f > fr

FIGURE 12.4   Phasor diagram of the series RLC circuit.

With f < fr, the negative reactance Xc of capacitor C exceeds the positive
reactance XL of inductor L. Hence, the overall reactance is capacitive.
Current I leads the applied voltage V.


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