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

122 Chapter Four
always assumed to be V rms values unless otherwise stated). Therefore,
the peak voltage output from the T1 secondary is
Peak (rms value )1.414 (12 volts AC)1.414 16.968 volts peak
For discussion purposes, the 16.968 volts can be rounded off to 17 volts.
The previous calculation tells us that for each full cycle, the T1 secondary
will output one positive 17-volt peak half-cycle, and one negative
17 volt peak half-cycle. The negative half-cycles are blocked by D1, allowing
R load
to receive only the positive half-cycles. The actual peak voltage
across R load
will be the 17-volt positive peak, minus the 0.7-volt forward
threshold voltage being dropped by D1. In other words, 16.3-volt positive
peaks will be applied to R load
, as shown in Fig. 4-5.
The diode circuit illustrated in Fig. 4-4 is called a half-wave rectifier,
because only one-half of the full AC cycle is actually applied to the
load. However, it would be much more desirable to utilize the full AC
cycle. The circuits shown in Fig. 4-6 are designed to accomplish this, and
they are called full-wave rectifiers.
The full-wave bridge rectifier illustrated in Fig. 4-6 is the more common
type of AC rectifier. It consists of four diodes. The operation of a fullwave
bridge rectifier can be examined by referring to Fig. 4-7. When the
transformer secondary outputs a half-cycle with the polarity shown in
Figure 4-6
Two types of
full-wave rectifiers.
R L
Full-wave bridge rectifiers
(two common methods
of illustration)
R L
Full-wave rectifier
utilizing a center-tapped
transformer
R L