Series Inductor Filter

Series Inductor Filter.

series-inductor-filter

In this arrange­ment a high value inductor or choke L is connected in series with the rectifier element and the load, as illustrated in figure. The filtering action of an inductor filter de­pends upon its property of opposing any change in the current flowing through it. When the output current of the rectifier increases above a certain value, energy is stored in it in the form of magnetic field and this energy is given up when the output current falls below the average value. Thus by placing a choke coil in series with the rectifier output and load, any sudden change in current that might have occurred in the circuit without an inductor is smoothed out by the presence of the inductor L.

The function of the inductor filter may be viewed in terms of impedances. The choke offers high impedance to the ac components but offers almost zero resistance to the desired dc components. Thus ripples are removed to a large extent. Nature of the output voltage without filter and with choke filter is shown in figure.

For dc (zero frequency), the choke resistance R_c in series with the load resistance R_L forms a voltage divider and dc voltage across the load is given as

where V_dc is dc voltage output from a full-wave rectifier. Usually choke coil resistance Rc, is much small than R_L and, therefore, almost entire of the dc voltage is available across the load resistance R_L.

Since the reactance of inductor increases with the increase in frequency, better filter­ing of the higher harmonic components takes place, so effect of third and higher harmonic voltages can be neglected.

As obvious from equation , if choke coil resistance R_c is negligible in comparison to load resistance R_L, then the entire dc component of rectifier output is available across 2 R_L and is equal to — V_L max. The ac voltage partly drops across X_L and partly over R_L