RECTIFIER WITH FILTER CAPACITOR BY AARTHI.M(221710303001)

We have seen that output of a halfwave or a fullwave rectifier circuit is not pure dc but it contains fluctuations or ripple, which are undesired.To minimise this ripple content in the output filters circuits are used.These circuits are connected between the rectifier and load.

An AC input is applied to the rectifier.But the output of the rectifier there will be DC and ripple voltage present which is the input to the filter.Ideally the output of the filter should be pure the whose frequency is zero.Here,the filter circuit will try to minimise the ripple at the output as far as possible .

Basically the ripple is AC, that is varying with time while DC is a constant with time.hence, in order to separate DC from ripple ,the filter circuit should use component which have widely different impedence for ACand DC.Two such components are inductance and capacitance.Ideally , the inductance acts as a short circuit for dc but it has a large impedence for AC.Similarly ,the capacitor acts as open for DC and almost short for DC.If the value of capacitance is sufficiently large enough.  

NOTE: 1.   Hence,in a filter circuit ,the inductance is always connected in series with the load.

             2.The inductance used in filter circuits is also called as "choke".

             3. Similarly since the capacitance is open for DC hence it cannot be connected in series with                  the load.

             4.It is always connected in shunt arm ,parallel to the load.

There are basically two types of filter circuits:

1. capacitor input filter
2. choke input filter

OPERATION OF FILTER WITH HALF WAVE RECTIFIERFilter uses a single capacitor in parallel with the load, represented by the resistance Rl .In order to minimise the ripple in the output the capacitance C used in the filter circuit   is quite large , of the order of tens of micro farads. During the positive quarter cycle of the input signal the diode is forward biased .this charges the capacitor C  to the peak value of input .Practically the capacitor C charges to 0.7 volts,due to diode forward voltage drop.This initial charging happens only once.Immediately when the power is turned on.when the input starts decreasing below its peak value,The capacitor remains charged and the ideal diode gets reverse biased.

OPERATION WITH FULL RECTIFIER

Through the above mentioned process it also works with the full wave rectifier.