CHAPTER 33 APPLIED ELECTRICITY H We will now look at the use of diodes in terms of three types of rectifier.
Rectifier Rectification is the conversion of alternating current (a.c.) to direct current (d.c.).
Half-wave rectifier
A half-wave rectifier consists of a single diode, which allows current in the forward bias only (Fig. 33.22). When the a.c. reverses direction, the diode blocks it in reverse bias. This results in only the forward voltage passing current and presents a pulsing waveform (Fig. 33.23). A half-wave rectifier is inefficient as it loses energy and gives an inconsistent supply.
a.c. input + V
0 V – V
Rectifier output
voltage source
Full-wave rectifier
A full-wave rectifier consists of four diodes in a circuit, forming a bridge network (also known as a bridge rectifier). Figs 33.24 and 33.25 demonstrate how a full-wave rectifier is capable of allowing current to pass while going in both directions.
A
voltage source
a.c. B FIG. 33.24 A full-wave rectifier circuit
• Forward from AãB: Current travels through diode 2, then out through the load resistor, and then back through diode 4.
• Reverse from BãA: Current travels through diode 3, then through load resistor, then back through diode 1.
• The output is now more efficient but it is still of a pulsing nature and not as uniform as a steady d.c. waveform.
4
12 3
load
a.c. input + V
0 V – V
Rectifier output
+ V 0 V – V
Time a.c. load FIG. 33.22 A half-wave rectifier circuit
+ V 0 V – V
Time
Time FIG. 33.23 A half-wave rectifier voltage output
Time FIG. 33.25 A full-wave rectifier voltage output
