The main function of a Full Wave Rectifier is to convert a pulsating AC signal into a DC signal. As the name suggests, this full wave rectifier rectifies both the half cycles of the input AC signal. Today we will discuss a detailed description of the full wave rectifier. Here we will learn about its connection, working principle. But the DC signal acquired at the output still has some waves which are called ripples. To decrease these ripples at the output a filter (Capacitor Filter) is used.
What is a Full Wave Rectifier with Filter?
In the full wave rectifier circuit using a capacitor filter, capacitor C is situated across the RL load resistor. The working of this rectifier is almost the same as a half wave rectifier. The only difference is half wave rectifier has just one half-cycle (positive or negative) whereas in full wave rectifier has two half-cycles (positive and negative).
As the input AC voltage is applied throughout the positive half cycle, then the diode D1 gets forward biased and permits current flow while the diode D2 gets reverse biased & blocks the current flow.
Throughout the above half cycle, the current in the diode D1 gets the filter and make active the capacitor. But, the capacitor charging will occur just when the voltage which is applied is upper 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 in the circuit, then the capacitor will get charged immediately.
Throughout this transmission time, the capacitor gets charged to the highest value of the input voltage supply. The capacitor includes a highest charge at the quarter waveform in the positive half cycle. In the end, the voltage supply is equivalent to the voltage of the capacitor. Once the AC voltage begins falling and turns into less than the voltage of the capacitor, after that the capacitor begins discharging gradually.
As the input AC voltage supply gets the negative half cycle, then the diode D1 gets reverse biased but the diode D2 is forward biased. Throughout the negative half cycle, the current flow in the diode D2 gets the filter to charge the capacitor. But, the capacitor charging occurs simply while the applied AC voltage is higher than 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 higher than the voltage of the capacitor, the capacitor gets charging. In both the half cycles, the flow of current will be in the same 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.
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Full Wave Rectifier Working And Operation
The working and operation of a full wave rectifier is too simple. In the below circuit diagram, four diodes are arranged in the form of a bridge. During full wave rectification, the two diodes become forward biased and another two diodes get reverse biased. The load resistance RL is connected to the bridge through points B and D.
During the positive half cycle, diodes D2 and D4 are in forward bias while diodes D1 and D3 are reverse biased and the current flow respectively through the output terminal D2, and D4. During the negative half cycle, diodes D1 and D3 are in forward bias, and diodes D4 and D2 are in reverse biased and the current flows through D1 and D3. The direction of both current ways is the same.
Filtering is the process of the DC signal done by using a capacitor. The output from the full wave rectifier is not a pure DC voltage. This will be mixed with some noises called ripples. Therefore, it needs to be filtered by connecting a capacitor in parallel to the output of the full wave rectifier. The capacitor charges and discharges during a cycle giving a pure and rectified DC voltage as output. But we can’t remove all the ripples from the rectifier. So, a capacitor of 100 uF/25V is connected to the output of the rectifier circuit. This capacitor acts as a filtering capacitor which diverts all the AC through it to the ground. At the output, the mean DC voltage left is filtered and ripples free. A capacitor of 0.1 uF is used for filtering the AC signal.
Full Working Principle Read Full Wave Rectifier Working
Peak Inverse Voltage of a Full Wave Rectifier
Now let’s discuss peak inverse voltage (PIV) of a full wave rectifier by analyzing the above circuit. At any instant when the transformer secondary voltage attains positive peak value Vmax, diodes D1 and D3 will be forward biased and the diodes D2 and D4 will be reverse biased. As we consider ideal diodes, the forward biased diodes D1 and D3 will have zero resistance. This means the voltage drop across the diodes D1 and D3 will be zero. This will result in the entire transformer secondary voltage being developed across the load resistance RL.
Thus PIV of a rectifier = Vmax
Advantages and Disadvantages of Full Wave Rectifier Over Half Wave Rectifier
- Efficiency is double for a full wave rectifier. The reason is that a half wave rectifier makes use of only one half of the input signal. A bridge rectifier makes use of both halves and hence double efficiency.
- The residual ac ripples are very low in the output of a bridge rectifier. The same ripple percentage is very high in the half wave rectifier. A simple filter is enough to get a constant dc voltage from the bridge rectifier.
- We know the efficiency of the full wave bridge rectifier is double that of the half wave rectifier. This means higher output voltage, Higher transformer utilization factor, and higher output power.