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@Prajakta Kelapure • 20 Oct, 2016
1. The output from the rectifier circuits is not purely DC but consist of some amount of AC component into it. This AC component is known ripples.

2. These ripples are more in half wave rectifiers and comparatively less in full wave rectifier. The amount of ripples reduces if the number of phases is increased.

3. Such supply which consists of ripples is not suitable for driving sophisticated electronic devices. Thus the output for such devices should be purely DC.

4. This is achieved by using filter circuit or smoothing circuit which removes the AC component.

5. This means that a filter circuit should be placed in between the rectifier and the load.

6. Thus a filter circuit is a device that converts pulsating output of the rectifier into steady DC level.

7. Filter Circuits consist of the combination of inductors L and the capacitors C.

8. L allows only the DC component to pass will the C allow only the AC to pass


9. Filter circuits are divided into Active and Passive:

Active filter
consist of active and passive components and it requires external power supply. Operational Amplifiers consisting of transistor(active component) are used in the making of Active filters.

Passive filters
consist of all passive elements such as Resistor, Capacitors and Inductors which does not depend on External power supply.
  • Series Inductor
  • Shunt Capacitor
  • Choke Input or L section
  • Capacitor Input or π filter
  • R-C filter
10. Filters are also classified as Analog and digital filter. Analog filter is much used in signal processing. Digital filter is a system used to perform mathematical operation to reduce or enhance certain aspect of the signal.

11. Filter are also classified as -
  • High Pass: Allows all frequencies above the certain limit specified called as the cut off level
  • Low Pass: Aloows all frequencies below the cut off
  • Band pass: Allows the frequencies within that particular band
  • Band Stop: Rejects the frequencies within that particular band
  • All Pass : Pass all the frequencies.
12. They are also classified into linear filter which obeys superposition theorm and shift invariance while Non linear filter does not obey this principle that is the result vary in non intuitive manner.

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