1-22
Figure 1-19.—Reverse-biased PN junction.
Therefore, when a PN junction is reverse biased, there will be no current flow because of majority
carriers but a very small amount of current because of minority carriers crossing the junction. However, at
normal operating temperatures, this small current may be neglected.
In summary, the most important point to remember about the PN junction diode is its ability to offer
very little resistance to current flow in the forward-bias direction but maximum resistance to current flow
when reverse biased. A good way of illustrating this point is by plotting a graph of the applied voltage
versus the measured current. Figure 1-20 shows a plot of this voltage-current relationship (characteristic
curve) for a typical PN junction diode.
Figure 1-20.—PN junction diode characteristic curve.
To determine the resistance from the curve in this figure we can use Ohm’s law:
