3-9
Figure 3-10.—Complete full-wave rectifier.
During the first half-cycle (as indicated by solid arrows) the plate of V1 is positive with respect to
ground and the plate of V2 is negative. As shown, current flows from ground (center tap), up through the
load resistor (RL), through diode V1 to point A. In the transformer, current flows from point A, through
the upper winding and back to ground (center tap). When V1 conducts, it acts like a closed switch so that
the positive half-cycle is felt across the load.
During the second half-cycle (broken lines), the polarity of the applied voltage has reversed Now the
plate of V2 is positive with respect to ground and the plate of V1 is negative. Only V2 can conduct.
Current now flows, as shown, from ground (center tap), up through the load resistor (R
L), through diode
V2 to point B of T1. In the transformer, current flows from point B up through the lower windings and
back to ground (center tap). Notice that the current flows across the load resistor (R
L) in the SAME
DIRECTION for both halves of the input cycles.
The output waveform from the full-wave rectifier consists of two pulses of current (or voltage) for
each cycle of input voltage. The ripple frequency at the output of the full-wave rectifier is therefore
TWICE THE LINE FREQUENCY.
The higher ripple frequency at the output of a full-wave rectifier has a distinct advantage: Because of
the higher pulse frequency, the output is closely approximate to pure dc. This higher frequency also
makes filtering much easier than the output of the half-wave rectifier.
In terms of peak value, the average value of current and voltage at the output of the full-wave
rectifier is twice as great as the average current or voltage at the output of the half-wave rectifier. The
relationship between peak and average values is illustrated in figure 3-11.
Figure 3-11.—Peak and average values for a full-wave rectifier.
