Thus for the ripple component with a frequency of ‘f’ megahertz, the capacitor ‘C’ will offer a very low impedance. Through this energy storage and delivery process, the time duration during which the current flows through the load resistor gets increased and the ripples are decreased by a great amount. When the rectifier is not conducting, this energy charged by the capacitor is delivered back to the load. This capacitor, when placed across a rectifier gets charged and stores the charged energy during the conduction period. Shunt Capacitor FilterĪs the name suggests, a capacitor is used as the filter and this high value capacitor is shunted or placed across the load impedance. It is always better to use a shunt capacitor (C) with series inductor (L) to form an LC Filter. A simple series inductor filter may not be properly used. So, the series inductor filter is mostly used in cases of high load current or small load resistance. It should be noted that a decrease in the value of load resistance or an increase in the value of load current will decrease the amount of ripples in the circuit. This is because of the fact that with the increase in frequency, the reactance of the inductor also increases. The effect of higher harmonic voltages can be easily neglected as better filtering for the higher harmonic components take place. In this case, the value of Ri is negligibly small when compared to RL. Vdc is the output from a full wave rectifier. The waveform below shows the use of inductor in the circuit.įrom the circuit, for zero frequency dc voltage, the choke resistance Ri in series with the load resistance RL forms a voltage divider circuit, and thus the dc voltage across the load is Thus all the sudden changes in current that occurs in the circuit will be smoothened by placing the inductor in series between the rectifier and the load. When the rectifier output current increases above a certain value, energy is stored in it in the form of a magnetic field and this energy is given up when the output current falls below the average value. Thus the ripple components will be eliminated. In other words, the inductor offers high impedance to the ripples and no impedance to the desired dc components. The inductor carries the property of opposing the change in current that flows through it. Series Inductor FilterĪs the name of the filter circuit suggests, the Inductor L is connected in series between the rectifier circuit and the load. The circuit diagram of a full wave rectifier with a series inductor filter is given below. All the combinations and their working are explained in detail below. Capacitor is used so as to block the dc and allows ac to pass. Inductor is used for its property that it allows only dc components to pass and blocks ac signals. The filter circuit can be constructed by the combination of components like capacitors, resistors, and inductors. Thus the output of the filter circuit will be a steady dc voltage. The filter is a device that allows passing the dc component of the load and blocks the ac component of the rectifier output. Thus, the output of the rectifier has to be passed though a filter circuit to filter the ac components. If the rectifier output is smoothened and steady and then passed on as the supply voltage, then the overall operation of the circuit becomes better. For most applications the supply from a rectifier will make the operation of the circuit poor. For most supply purposes constant dc voltage is required than the pulsating output of the rectifier. Such supply is not useful for driving complex electronic circuits. The ripples will be minimum for 3-phase rectifier circuits. These ripples will be the highest for a single-phase half wave rectifier and will reduce further for a single-phase full wave rectifier. Apart from the dc component, this pulsating dc voltage will have unwanted ac components like the components of its supply frequency along with its harmonics (together called ripples). We have learnt in rectifier circuits about converting a sinusoidal ac voltage into its corresponding pulsating dc.
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