4-29 Now let's discuss the dc component of the applied voltage. Remember, a capacitor offers an infinite () impedance to the flow of direct current. The dc component, therefore, must flow through R_{L} and L1. As far as the dc is concerned, the capacitor does not exist. The coil and the load are therefore in series with each other. The dc resistance of a filter choke is very low (50 ohms average). Consequently, most of the dc component is developed across the load and a very small amount of the dc voltage is dropped across the coil, as shown in figure 4-26. Figure 4-26.—Dc component in an LC choke-input filter. As you may have noticed, both the ac and the dc components flow through L1. Because it is frequency sensitive, the coil 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 choke-input filter is improved when the filter is used in conjunction with a full-wave rectifier, as shown in figure 4-27. This is due to the decrease in the XCof the filter capacitor and the increase in the X_{L }of the choke. Remember, ripple frequency of a full-wave rectifier is twice that of a half-wave rectifier. For 60-hertz input, the ripple will be 120 hertz. The X_{C} of C1 and the X_{L} of L1 are calculated as follows: