3-29
Figure 3-35.—DC component in an LC choke-input filter.
As you may have noticed, both the ac and the dc components flow through L1, and because the coil
is frequency sensitive, it provides a large resistance to ac and a small resistance to dc. In other words, the
coil opposes any change in current. This property makes the coil a highly desirable filter component. Note
that the filtering action of the LC capacitor input filter is improved when the filter is used in conjunction
with a full-wave rectifier as shown in figure 3-36. This is due to the decrease in the XC of the filter
capacitor and the increase in the XL of the choke. Remember, the ripple frequency of a full-wave rectifier
is twice that of a half-wave rectifier. For a 60-hertz input, the ripple will be 120 Hertz. Let's briefly
calculate the X
C
of C1 and the XL of L1:
