Question
What is a filter circuit? Explain its functioning.
✓
Answer
→The rectified voltage is in the form of pulses of the shape of half sinusoilds. Though, it is unidirectional it does not have a steady value.
→To get steady dc output from pulsating voltage, the filter circuit is used. Filter circuits consist of only capacitor, only inductor or a combination of both. Since these additional circuits appear to filter out the ac ripple and give a pure dc voltage, so they are called filters.
• Functioning of a Filter Circuit :
→When the voltage across the capacitor is rising, it gets charged. If there is no external load, it remains charged to peak voltage of the rectified output.
→When there is a load, it 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.
→As shown in the fig., the rate of fall of the voltage across capacitor depends on the inverse product of capacitor C and the effective resistance $R_L$ used in the circuit and is called the time constant. To make the time constant large, value of C should be large. So capacitor input filters use large capacitors.
→The output voltage obtained by using capacitor input filter is nearer to the peak voltage of the rectified voltage.
→This type of filter is most widely used in power supplies.
→To get steady dc output from pulsating voltage, the filter circuit is used. Filter circuits consist of only capacitor, only inductor or a combination of both. Since these additional circuits appear to filter out the ac ripple and give a pure dc voltage, so they are called filters.
• Functioning of a Filter Circuit :
→When the voltage across the capacitor is rising, it gets charged. If there is no external load, it remains charged to peak voltage of the rectified output.
→When there is a load, it 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.
→As shown in the fig., the rate of fall of the voltage across capacitor depends on the inverse product of capacitor C and the effective resistance $R_L$ used in the circuit and is called the time constant. To make the time constant large, value of C should be large. So capacitor input filters use large capacitors.
→The output voltage obtained by using capacitor input filter is nearer to the peak voltage of the rectified voltage.
→This type of filter is most widely used in power supplies.
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