LC Filter and pi filter

•  LC FILTER

                                                           

There is not much of an explanation left if you have understood how a inductor and capacitor filter works (working of both filters are given in my previous posts).Let's recapitulate,in an inductor filter the ripple factor is directly proportional to the load resistance but in capacitor filter it is inversely proportional to the load resistance.So the question is what happens if both are present in the same circuit.The answer is that in such a circuit ripple factor becomes almost independent of load resistance.The formula of ripple factor is given by the following expression...............................
                                                           

From the formula it is clear that the ripple factor doesn't depends upon load resistance.

• Pi-Filter
  

As you can see from the figure only an additional capacitor is added to the LC filter making it an pi-filter.This type of filter is used when a high DC voltage at low load current is required .As usual the pulsating voltage from the rectifier circuit is fed into the pi-filter circuit.The capacitor (C1) provides low reactance to the ac components as well as high reactance to dc components.The dc components are passed through the inductor as it provides low reactance to the dc components but high reactance to ac components.The capacitor (C2) operates in a similar way as that of  capacitor C1. As a result of this only dc component is available at the output.The formula for ripple factor is given by the following expression ............

There is one disadvantage in pi-filter which is that ripple factor depends upon load resistance whereas in LC filter it is independent.That's it!!!