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Sec. 2–1 Properties of Signals and Noise 39 Example 2–2 EVALUATION OF POWER Let the circuit of Fig. 2–2 contain a 120-V, 60-Hz fluorescent lamp wired in a high-power–factor configuration. Assume that the voltage and current are both sinusoids and in phase (unity power factor), as shown in Fig. 2–3. † The DC value of this (periodic) voltage waveform is v(t) T 0 V V rms 0 1 –– 2 T 0 T 0 t (a) Voltage i(t) I I rms 0 1 –– 2 T 0 T 0 t (b) Current p(t) VI 0 1 –– T 2 0 T 0 t 1 ––2 VI (c) Instantaneous Power Figure 2–3 Steady-state waveshapes for Example 2–2. † Two-lamp fluorescent circuits can be realized with a high-power–factor ballast that gives an overall power factor greater than 90% [Fink and Beaty, 1978].
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Sec. 2–1 Properties of Signals and Noise 39<br />
Example 2–2 EVALUATION OF POWER<br />
Let the circuit of Fig. 2–2 contain a 120-V, 60-Hz fluorescent lamp wired in a high-power–factor<br />
configuration. Assume that the voltage and current are both sinusoids and in phase (unity power<br />
factor), as shown in Fig. 2–3. † The DC value of this (periodic) voltage waveform is<br />
v(t)<br />
T 0<br />
V<br />
V rms<br />
0<br />
1<br />
–– 2<br />
T 0 T 0 t<br />
(a) Voltage<br />
i(t)<br />
I<br />
I rms<br />
0<br />
1<br />
–– 2<br />
T 0 T 0 t<br />
(b) Current<br />
p(t)<br />
VI<br />
0<br />
1<br />
–– T 2 0 T 0<br />
t<br />
1 ––2 VI<br />
(c) Instantaneous Power<br />
Figure 2–3 Steady-state waveshapes for Example 2–2.<br />
† Two-lamp fluorescent circuits can be realized with a high-power–factor ballast that gives an overall power<br />
factor greater than 90% [Fink and Beaty, 1978].
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