(1) At time (t1) the voltage with respect to ground will be positive (+)
and an electron current will be flowing upward through the resistor.
(2) At time (t3) the voltage with respect to ground will be negative
(-) and an electron current will be flowing downward through the resistor.
(3) Here we can see that the direction of the voltage is controlling the
direction of electron current through the resistor. So the current first flows in
an upward direction; then, as time passes, it reverses. It alternates once each
cycle or revolution of the rotor.
c. The amount of current through the resistor is determined by its value of
resistance. With a very large resistive value, only a small current will flow.
With a very small resistive value, a large current will flow. The values of
resistance lay between two extremes. The maximum value of resistance is an open
circuit; the minimum value of resistance is a short circuit. These extreme values
of resistance are approached in the rectifying diode. When the diode is forward
biased, it exhibits nearly a short circuit. When it is reverse biased, it
approximates an open circuit.
d. Figure 28 shows an AC potential being applied to a resistor and diode
connected in series. Since the voltage potential is alternating above and below
ground or zero potential, the diode will experience times of forward bias at (t1)
and reverse bias at (t2). The diode becomes forward biased any time after the
voltage potential leaves zero and goes positive. The diode becomes reverse biased
any time after the voltage potential leaves zero and goes negative.
Figure 28.
Half-wave rectifier.
(1) When the diode is forward biased, maximum current will be allowed to
flow through the resistor thereby developing a positive half cycle.
(2) When the diode is reversed biased, minimum current will be allowed
to flow through the resistor. If the minimum current approaches zero, then the
voltage developed across the resistor will also approach zero. For all practical
purposes it is said to be zero, since the value of positive voltage is much greater
than negative.
(3) This circuit is called a half-wave rectifier because only half of
the entire cycle of AC voltage is allowed to be developed across the resistor (fig
29).
OS 010, 1-P15
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