FILTERS|Capacitor filter|Inductor filter| LC FILTER|(Pi) FILTER|

 FILTERS

The filter is a circuit that contains only passive components. It is used to convert pulsating DC signal into a steady (pure) DC signal. Generally, the output of the rectifier contains DC components as well as AC components. The presence of AC components in the DC signal is undesirable. So it must be removed by using filters. The filter circuit removes (or minimizes) the unwanted AC signal present in the rectified output DC signal.

The various types of filters are

(i) Capacitor filter. 

(ii) Inductor filter

 (iii) LC (Inductor Capacitor filter)

 (iv) pi filter

(v) RC filter

CAPACITOR FILTER

The circuit diagram of a capacitor filter is shown in fig. The capacitor C is placed across the rectifier output and also parallel to the load resistor RL. The pulsating DC voltage of the rectifier output is applied across the capacitor. The capacitor opposes the sudden variation of the voltage applied across to it. During the rising voltage of the input; the capacitor charges, and during the falling voltage of the input the capacitor discharges through RL.

capacitor filter: capacitor C is placed across the rectifier output and also parallel to the load resistor RL

At the maximum input voltage, the capacitor charges to a maximum voltage Vm. In between the input voltage levels, the capacitor does not discharge the full Vm voltage. The next cycle of the input again charges the capacitor to Vm voltage. So it will reduce the amount of AC components present in the DC signal. The input and output signal waveforms are shown in fig.

Optput of capacitor filter:At the maximum input voltage, the capacitor charges to a maximum voltage Vm. In between the input voltage levels, the capacitor does not discharge the full Vm voltage

Inductor filter

The circuit diagram of an Inductor filter is shown in fig. The inductor opposes the sudden variation of current which is connected in series with the load resistor RL. So the inductor reduces the number of variations of ripple current. Hence AC ripple will be reduced. The input and output waveforms are shown in fig.

        

Inductor filter:The circuit diagram and output of inductor filter

 LC FILTER

This filter is a combination of capacitor and inductor filters. It provides low ripples than capacitor and inductor filters. The circuit diagram of the LC filter is shown in fig.

LC filter:the circuit diagram and output waveform of LC filter.

The inductor provides high reactance to the AC components of the rectified output and it also blocks the AC components. It passes the DC components to the load. The AC component is also once again filtered by capacitor C. So the output contains almost only pure DC components. The input and output signal waveforms are shown in fig.

 (Pi) FILTER

The pi filter contains two capacitors and only one inductor, form a symbol of it. It is also called capacitor input filter, as shown in fig. The capacitor C 1 offers low reactance to the ac components of the rectified output. So the AC components are bypassed to ground through C,.

The inductor L provides high reactance to the AC components. So the AC components are dropped across the inductor, it passes only the DC components.

Pi filter:the circuit diagram of Pi filter.

The capacitor C again removes the AC components present in the DC signal. As a result, the output contains only pure DC components. The large values of capacitors produce high DC output voltage.