3-25 As a result, when the pulsating voltage is first applied to the LC choke-input filter, the inductor or filter choke (L1) produces a counter emf that opposes the constantly increasing input voltage. The net result is to effectively prevent the rapid charging of the filter capacitor (C1). Thus, instead of reaching the peak value of the input voltage, C1 only charges to the average value of the input voltage. After the input voltage reaches its peak and decreases sufficiently, the capacitor (C1) attempts to discharge through the load resistance (R_{L}). C1 will attempt to discharge as indicated in figure 3-29. Because of its relatively long discharge time constant, C1 can only partially discharge. Figure 3-29.—LC choke-input filter (discharge path). The larger the value of the filter capacitor, the better the filtering action. However, due to the physical size, there is a practical limitation to the maximum value of the capacitor. The inductor or filter choke (L1) maintains the current flow to the filter output (capacitor C1 and load resistance R_{L}) at a nearly constant level during the charge and discharge periods of the filter capacitor. The series inductor (L1) and the capacitor (C1) form a voltage divider for the ac component (ripple) of the applied input voltage. This is shown in figure 3-30. As far as the ripple component is concerned, the inductor offers a high impedance (Z) and the capacitor offers a low impedance. As a result, the ripple component (E_{r}) appearing across the load resistance is greatly attenuated (reduced). Since the inductanceof the filter choke opposes changes in the value of the current flowing through it, the average value of the voltage produced across the capacitor contains a much smaller value of ripple component (E_{r}), as compared with the value of ripple produced across the coil. Figure 3-30.—LC choke-input filter (as voltage divider).

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