______________________________________________________________ Solid State Power Supplies
rectifier. This is because the secondary of the power transformer in the full-wave rectifier
is center tapped; therefore, only half the source voltage goes to each diode.
4-23. There is also a rectifier that produces the same peak voltage as a half-wave rectifier
and the same ripple frequency as a full-wave rectifier. When four diodes are connected as
shown in Figure 4-8, the circuit is called a BRIDGE RECTIFIER. The input to the circuit
is applied to the diagonally opposite corners of the network and the output is taken from
the remaining two corners.
Figure 4-8. Bridge Rectifier
4-24. One complete cycle of operation will be discussed to help you understand how this
circuit works. We will use a transformer that is working properly and where there is a
positive potential at point A and a negative potential at point B. The positive potential at
point A will forward bias D3 and reverse bias D4. The negative potential at point B will
forward bias Dl and reverse bias D2. At this time D3 and D1 are forward biased and will
allow current flow to pass through them (D4 and D2 are reverse biased and will block
current flow). The path for current flow is from point B through Dl, up through RL,
through D3, through the secondary of the transformer back to point B. The solid arrows
indicate this path. Waveforms (1) and (2) can be observed across Dl and D3.
4-25. One-half cycle later; the polarity across the secondary of the transformer reverses,
forward biasing D2 and D4 and reverse biasing D1 and D3. Current flow will now be from
point A through D4, up through RL, through D2, up through the secondary of T1, and back
to point A. The broken arrows indicate this path. Waveforms (3) and (4) can be observed
across D2 and D4. You should have noted that the current flow through RL is always in the
same direction. In flowing through RL this current develops a voltage corresponding to that
shown in waveform (5). Since current flows through the load (RL) during both half cycles
of the applied voltage, this bridge rectifier is a full-wave rectifier.
4-26. One advantage of a bridge rectifier over a conventional full-wave rectifier is that
with a given transformer, the bridge rectifier produces a voltage output that is nearly twice
23 June 2005