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What is a filter ? With the help of a circuit diagram describe the role of a capacitor in filtering. Draw input and output waveforms too. |
Answer» Solution :In the output obtained from a full-wave rectifier, the output is unidirectional but pulsating one. To get steady output we use a filter circuit which FILTERS the a.c. ripple and gives a pure d.c. VOLTAGE. A capacitor based filter circuit has been shown in . When the voltage across the capacitor is rising, it gets charged. In the absence of external load it remains charged to the peak voltage of the rectified output. But in the presence of a load, the capacitor gets discharged through the load and the voltage across it begins to fall. In the next half-cycle of rectified output it again gets charged to the peak value. If product of capacitance C and load resistance `R_(L)` is LARGE, then rate of fall of the voltage across the capacitor is slow one. HENCE, the output voltage obtained by using capacitor input filter is almost equal to the peak voltage of the rectified output if value of capacitance C and `R_(L)` is high enough. The a.c. input and filtered output waveforms have been shown in. 
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