Page 67 - Power Quality in Electrical Systems

50 Chapter Four

i(t) ∆i PP

I 0

t
(a)
D
i(t)

L

± R C
V CC

(b)
Figure 4.9 DC + ripple. (a) Waveform. (b) DC/DC converter circuit that pro-
duces this waveform. In this case, i(t) is the inductor current.

DC waveform ripple
A DC waveform with a finite peak-peak ripple (Figure 4.9) is generated
by a variety of switching circuits, including motor drives and DC/DC
converters. This waveform has a DC value I and a peak-peak ripple of
o
∆i . The rms value of this waveform is
pp

1 i pp 2
I rms 5 I o Å 1 1 a ba 2I o b
3

Triangular ripple
A triangular ripple waveform (Figure 4.10) is typical of the capacitor cur-
rent in a variety of switching circuits. In this case, the rms value of the
current is

i pp
I rms 5
2!3