4-7
Q6. If the output of a half-wave rectifier is 50-volts peak, what is the average voltage?
Q7. In addition to stepping up or stepping down the input line voltage, what additional purpose does
the transformer serve?
The Conventional Full-Wave Rectifier
A full-wave rectifier is a device that has two or more diodes arranged so that load current flows in
the same direction during each half cycle of the ac supply.
A diagram of a simple full-wave rectifier is shown in figure 4-5. The transformer supplies the source
voltage for two diode rectifiers, D1 and D2. This power transformer has a center-tapped, high-voltage
secondary winding that is divided into two equal parts (W1 and W2). W1 provides the source voltage for
D1, and W2 provides the source voltage for D2. The connections to the diodes are arranged so that the
diodes conduct on alternate half cycles.
During one alternation of the secondary voltage, the polarities are as shown in view A. The source
for D2 is the voltage induced into the lower half of the secondary winding of the transformer (W2). At the
specific instant of time shown in the figure, the anode voltage on D2 is negative, and D2 cannot conduct.
Throughout the period of time during which the anode of D2 is negative, the anode of D1 is positive.
Since the anode of D1 is positive, it conducts, causing current to flow through the load resistor in the
direction shown by the arrow.
Figure 4-5A.—Full-wave rectifier. POSITIVE ALTERNATION
View B shows the next half cycle of secondary voltage. Now the polarities across W1 and W2 are
reversed. During this alternation, the anode of D1 is driven negative and D1 cannot conduct. For the
period of time that the anode of D1 is negative, the anode of D2 is positive, permitting D2 to conduct.
Notice that the anode current of D2 passes through the load resistor in the same direction as the current of
D1 did. In this circuit arrangement, a pulse of load current flows during each alternation of the input
cycle. Since both alternations of the input voltage cycle are used, the circuit is called a FULL-WAVE
RECTIFIER.
