The basic half-wave rectifier circuit and the input and output waveforms are shown in the diagram. A half-wave rectifier conducts only during the positive half cycle. It allows only one half of an AC waveform to pass through the load, RL, hence, the name half-wave rectifier. During the positive half cycle, the diode is forward biased and will act as a short circuit, allowing the waveform to pass through the load. During the negative half cycle, the diode is reversed biased and will act as an open circuit.
Efficiency of the Half-wave Rectifier
Rectifier efficiency is defined as the ratio of DC power to the applied input AC power.
Rectifier efficiency, η = DC output power/input AC power
Idc= Im / π
The DC output power is given by: Pdc= I2dc x RL = (Im / π)2 x RL
The AC input power is given by: Pac= I2rms(rf + RL) , where rf is diode resistance.
For a half-wave rectified wave: Irms= Im / 2
Therefore, Pac=(Im/2)2 x (rf+RL)
Thus rectifier efficiency, η = DC output power/AC input power
= [(Im/π)2xRL] / [(Im/2)2x(rf+RL)]
= 0.406 RL/ (rf + RL)
= 0.406 / (1+rf/RL)
The efficiency will be maximum if rf is negligible as compared to RL
Therefore, maximum rectifier efficiency = 40.6%. This means only 40.6% of the input AC power is converted into DC power.