Half Wave and Full Wave Rectifier with Capacitor Filter

The filter is one type of electronic device mainly used to perform signal processing. The main function of this filter is to allow the ac components and blocks the dc components of the load. The filter circuit output will be a stable dc voltage. The construction of a filter circuit can be done with the basic electronic components like resistors, inductors, and capacitors. There are different types of filters available namely LPF (low pass filter), BPF (bandpass filter), HPF (high pass filter), capacitor filter, etc. The main function of the capacitor, as well as an inductor in this circuit, is, a capacitor allows the ac and blocks the dc, whereas an inductor permits only DC components to supply and blocks ac. This article discusses capacitor filter using half wave rectifier and full wave rectifier.

What is a Capacitor Filter?

A typical capacitor filter circuit diagram is shown below. The designing of this circuit can be done with a capacitor (C) as well as load resistor (RL). The rectifier’s exciting voltage is given across the terminals of a capacitor. Whenever the voltage of the rectifier enhances then the capacitor will be charged as well as supplies the current to the load.

Capacitor Filter
                                                               Capacitor Filter

At the last part of the quarter phase, the capacitor will be charged to the highest rectifier voltage value that is denoted with Vm, and then the voltage of the rectifier starts to reduce. As this happens, the capacitor starts discharging through the voltage across it and load. The voltage across the load will reduce little only because the next peak voltage occurs instantaneously to charge the capacitor. This procedure will repeat many times and the output waveform will be seen that very slight ripple is missing in the output. Furthermore, the output voltage is superior because it remains significantly close to the highest value of the output voltage of the rectifier.

Capacitor Filter Input
                   Capacitor Filter Input

A capacitor gives an infinite reactance to DC .For DC, f=0

Xc = 1/ 2пfc = 1/2п x 0 x C = infinite

Therefore, a capacitor doesn’t permit DC to flow through it.

Capacitor Filter Output
                    Capacitor Filter Output

The capacitor filter circuit is very famous due to its features like low cost, less weight, small size, & good characteristics. The capacitor filter circuit is applicable for small load currents.

Half Wave Rectifier with Capacitor Filter

The main function of half wave rectifier is to change the AC (Alternating Current) into DC (Direct Current). However, the acquired output DC is not pure and it is an exciting DC. This DC is not constant and varies with time. Whenever this changing DC is given to any type of electronic device, then it may not function correctly, and that may get damaged. Due to this reason, it will not be applicable in most of the applications.

Halfwave Rectifier with Capacitor Filter
              Halfwave Rectifier with Capacitor Filter

Thus, we require a DC that does not change with time. To overcome this problem and to get a smooth DC, there will be solutions namely filter. The energetic DC mainly includes both AC & DC components. So here filter is used to remove or reduce the AC components at the output. The filter can be built with components like resistors, capacitors, and inductors. The circuit diagram of half wave rectifier using a capacitor filter is shown above. This circuit is built with a resistor and capacitor. Here, the connection of the capacitor ‘C’ is in shunt with the ‘RL’ load resistor.

Whenever AC voltage is applied to the circuit throughout the positive half cycle, then the diode lets the flow of current through it. We know that the capacitor gives high-resistive lane to DC components as well as low-resistive lane to AC components. The flow of current always chooses to supply through a low resistance lane. So when the flow of current gets the filter, the ac components experience a low-resistance and dc components experience a high-resistance from the capacitor. The DC components flow through the load resistor (low resistance path).

Throughout the conduction time, the capacitor gets charged to the highest value of the voltage supply. As the voltage among the two plates of the capacitor is equivalent to the voltage supply, then it is said to be completely charged. When it gets charged then it holds the supply until the supply of i/p AC toward the rectifier achieves the negative half cycle.

Once the rectifier reaches to negative half cycle, the diode acquires reverse biased & stops letting the flow of current through it. Throughout this, the supply voltage is low then the voltage of a capacitor. Thus the capacitor releases all the stored current through the RL. This stops the o/p load voltage from falling to nil.

The charging and discharging of the capacitor mainly depends on when the input voltage supply is less or greater than the capacitor voltage. Once the rectifier reaches the positive half cycle, then the diode acquires forward biased & allows the flow of current to make the capacitor charge again. The capacitor filter through a huge discharge will generate an extremely smooth DC voltage. Therefore, a smooth DC voltage can be attained with this filter.

Full Wave Rectifier with Capacitor Filter

The main function of full wave rectifier is to convert an AC into DC. As the name implies, this rectifier rectifies both the half cycles of the i/p AC signal, but the DC signal acquired at the o/p still have some waves. To decrease these waves at the o/p this filter is used.

In the full wave rectifier circuit using a capacitor filter, the capacitor C is located across the RL load resistor. The working of this rectifier is almost the same as a half wave rectifier. The only dissimilarity is half wave rectifier has just one-half cycles (positive or negative) whereas in full wave rectifier has two cycles (positive and negative).

Fullwave Rectifier with Capacitor Filter
                    Full-wave Rectifier with Capacitor Filter

Once the i/p AC voltage is applied throughout the positive half cycle, then the D1 diode gets forward biased and permits flow of current while the D2 diode gets reverse biased & blocks the flow of current.

Throughout the above half cycle, the current in the D1 diode gets the filter and energizes the capacitor. But, the capacitor charging will occur just when the voltage which is applied is superior to the capacitor voltage. Firstly, the capacitor will not charge, as no voltage will stay among the capacitor plates. So when the voltage is switched on, then the capacitor will get charged immediately.

Throughout this transmission time, the capacitor gets charged to the highest value of the i/p voltage supply. The capacitor includes a highest charge at the quarter waveform in the positive half cycle. At this end, the voltage supply is equivalent to the voltage of the capacitor. Once the AC voltage begins falling & turns into less than the voltage of the capacitor, after that the capacitor begins discharging gradually.

As the i/p AC voltage supply gets the negative half-cycle, then the D1 diode gets reverse biased but the D2 diode is forward biased. Throughout the negative half cycle, the flow of current in the second diode gets the filter to charge the capacitor. But, the capacitor charging occurs simply while the applied AC voltage is superior to the voltage of the capacitor.

The capacitor in the circuit is not charged fully, so the charging of this does not occur instantly. Once the voltage supply becomes superior to the voltage of the capacitor, the capacitor gets charging. In both the half cycles, the flow of current will be in the similar direction across the RL load resistor. Thus we acquire either whole positive half cycle otherwise negative half cycle. In this case, we can get the total positive half cycle.

Halfwave & Fullwave Rectifier with Capacitor Filter Outputs
   Halfwave & Full-wave Rectifier with Capacitor Filter Outputs

Thus, this is all about what is a filter and capacitor filter, halfwave rectifier with capacitor filter and full wave rectifier with capacitor filter and its input as well as output waveforms. Furthermore, any queries regarding this concept or any technical information, please give your feedback by commenting in the comment section below. Here is a question for you, what are the applications of capacitor filter?

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