Half-Wave and Full-Wave Rectification
Because the reservoir capacitor recharge current must replace the current drawn from it during the nonconducting portion of the input cycle, both the peak recharge current and the residual ripple will be twice as large if half-wave rectification is employed, such as that shown in the circuit of Figure 5.1(h), in which the rectifier diode only conducts during every other half cycle of the secondary output voltage rather than on both cycles, as would be the case in Figure 5.1(b). A drawback with the layouts of both Figures 5.1(a) and 5.1(b) is that the transformer secondary windings only deliver power to the load every other half cycle, which means that when they do conduct, they must pass twice the current they would have had to supply in, for example, the bridge rectifier circuit shown in Figure 5.1(e). The importance of this is that the winding losses are related to the square of the output current (P i=R) so that the transformer copper losses would be four times as great in the circuit of Figure 5.1(b) as they would be for either of the bridge rectifier circuits of Figure 5.1(f). However, in the layout of Figure 5.1(b), during the conduction cycle in which the reservoir capacitor is recharged, only one conducting diode is in the current path, as compared with two in the bridge rectifier setups.
Many contemporary audio amplifier systems require symmetrical +ve and -ve power supply rails. If a mains transformer with a center-tapped secondary winding is available, such a pair of split-rail supplies can be provided by the layout of Figure 5.1(e) or, if component cost is of no importance, by the double bridge circuit of Figure 5.1(f). The half-wave voltage doubler circuit shown in Figure 5.1(g) is used mainly in low current applications where its output voltage characteristic is of value, such as perhaps a higher voltage, low-current source for a three-terminal voltage regulator.