Question

Describe two ways to smooth the signal from a rectifier , which one is preferred ?

Answer 1

Firstly , we will define rectifier ,rectifier is a device which is used to convert a AC signal into the pulsating DC and this process is known as rectification.There are two type of rectifier on the basis of phases i.e single phase and three phase rectifier .And further these rectifier are classified into two types i.e half and full wave rectifier.which may controlled ,uncontrolled or semi-controlled.After rectification we still don't get the perfect DC .Therefore we do smoothing to get approximately constant DC.hence we use Filter circuits.There are two methods, In first method filter circuits is connected in series with the load and in other method filter circuit are connected in parallel to the load.

To get a steady  voltage we need a circuit ,which will allow the passage of dc current and avoid the flow of ac current through the load.There are two ways

1)To drop the ac-voltage component at a part of the circuit - this means at a component connected in series to the load .

2) To bypass the ac-component of the current via a component connected in parallel to the load.

Method I :- It  requires something with a low resistance for dc and a high one for ac-components. Fitting therefore it is obviously an inductor.

Method II:- It requires something with a high resistance for dc and a low one for ac components. Fitting therefore it is obviously a capacitance.

The best smoothing can be achieved , if we use both methods in the same smoothing circuit. Therefore in power supplies for very high quality, you will find the circuit ,which is called as LC-smoothing circuits containing inductors and capacitors.

But inductors are bulky and are also known as chokes ,which are heavy and expensive. Therefore they are in most of the cases replaced by a resistor and then together with the capacitor so called RC-smoothing circuits.

But the resistors do not have to increased impedance for an ac-components (compared with their resistance for dc).Therefor R-C circuit is used that is Capacitor Smoothing.

Capacitor Smoothing

In capacitor smoothing ,we use capacitor for current smoothing ,which are called as smoothing capacitors .These capacitor are connected in parallel with the load ,across the output of the rectifier.And this filter circuit increases ,the average DC output level, because the capacitor acts like a storage device. The smoothing capacitor converts the rippled DC output of the rectifier into a smoother DC output .