At A, a half-wave rectifier circuit. At B, a full-wave center-tap rectifier circuit. At C, a full-wave bridge rectifier circuit.
The simplest rectifier circuit, called the half-wave rectifier (above figure A), has a single diode that chops off half of the ac cycle. The effective (eff ) output voltage from a power supply that uses a half-wave rectifier is much less than the peak transformer output voltage, as shown in below figure A. The peak voltage across the diode in the reverse direction can be as much as 2.8 times the applied rms ac voltage.
At A, the output of a half-wave rectifier. At B, the output of a fullwave rectifier. Note the difference in how the effective (eff ) voltages compare with the peak voltages.
Most engineers like to use diodes whose PIV ratings are at least 1.5 times the maximum expected peak reverse voltage. Therefore, in a half-wave rectifier circuit, the diodes should be rated for at least 2.8 × 1.5, or 4.2, times the rms ac voltage that appears across the secondary winding of the power transformer.
Half-wave rectification has shortcomings. First, the output is difficult to filter. Second, the output voltage can drop considerably when the supply is required to deliver high current. Third, halfwave rectification puts a strain on the transformer and diodes because it pumps them. The circuit works the diodes hard during half the ac cycle, and lets them loaf during the other half.
Half-wave rectification is usually adequate for use in a power supply that is not required to deliver much current, or when the voltage can vary without affecting the behavior of the equipment connected to it. The main advantage of a half-wave circuit is that it costs less than more sophisticated circuits.