Capacitor filter

(picture taken from wikipedia)

The above diagram is the Capacitor filter which generally comprises of a Diode rectifier circuit and a filter circuit where the capacitor is connected in parallel to the load resistance.When a pulasating DC voltage is applied across the capacitor,the capacitor filter removes voltage ripples upto a certain extent but if in addition to it a rectifier circuit is added the output voltage is much better(i.e you can say ripples are removed to a large extent).In order to understand how a capacitor filter works ,you need to have the clear picture of output waveforms in mind .

• Now what happens is that,in the positive half cycle of output voltage,the capacitor gets charged very quickly to the maximum value.The charging is almost instantaneous as there is no resistance.That is why the capacitor follows the charging voltage.When ac voltage starts to decrease from its maximum value ,the capacitor returns its charge.
• During the negetive half cycle,output voltage of the rectifier is zero which you can observe from (a) .So what happens is that the capacitor discharges through the load resistance at that time.The discharging time constant is RLC(i.e. the product of load resistance and capacitance).With the increase in the time constant discharge voltage of the capacitor will be less.In reality, you will be astonished to know that discharging time constant is about 100 times larger than that of charging time.This is the reason why a capacitor can maintain a perfect constant voltage across the load resistance.
• Due to the charging and discharging of the capacitor ,ripples evolve in the output voltage which is much less but still can't be ruled out.The ripple factor is expressed by gamma and is given by the following expression ..........................

                                     

where f is the frequency ,RL is load resistance and C is the capacitance.

In my next post I would explain the working of LC filter(inductor capacitor filter) and pi filter.Stay tuned.If you have any problem just let me know. Happy reading!!