Tab Electronics Guide to Understanding Electricity ... - Sciences Club

126 Chapter Four
Figure 4-10
Two leads of a
center-tapped
transformer 180
degrees out of phase
when ct is used as
the reference.
180° Out of phase
Center-tapped reference
Figure 4-11
Dual-voltage
rectification circuit.
D1
Bridge rectifier module
D3 R 1
D2
D4
R 2
The circuit in Fig. 4-12 utilizes this unused portion of the secondary
output to form another DC output of the opposite polarity. This can be
more easily understood by referring back to Figs. 4-11 and 4-8. Figure 4-12
is exactly the same circuit (with the same component labeling) as illustrated
in Fig. 4-11. Compare Fig. 4-12 with Fig. 4-8. Notice how the positive fullwave
rectification section of Fig. 4-12 is identical to the circuit illustrated
in Fig. 4-8. The circuit of Fig. 4-12 incorporates two additional diodes (D4
and D2) to form another full-wave output from the unused half-cycles.
Because of the orientation of the diodes, it will be negative in respect to
the circuit common. Dual-polarity power supplies are very common because
of their extensive use in operational amplifier and audio circuits; both of
which will be discussed later in this book. As in the case of the centertapped
full-wave rectifier circuit of Fig. 4-8, the voltages across R1 and R2
will be only half of the amplitude of the secondary rating.
Referencing
By now, you might be beginning to appreciate the importance of waveshapes
in the electrical and electronics fields. All of the waveshapes