2-13
Figure 2-9.—The forward-biased junction in a PNP transistor.
PNP REVERSE-BIASED JUNCTION.—In the reverse-biased junction (fig. 2-10), the negative
voltage on the collector and the positive voltage on the base block the majority current carriers from crossing
the junction. However, this same negative collector voltage acts as forward bias for the minority current
holes in the base, which cross the junction and enter the collector. The minority current electrons in the
collector also sense forward bias-the positive base voltage-and move into the base. The holes in the collector
are filled by electrons that flow from the negative terminal of the battery. At the same time the electrons
leave the negative terminal of the battery, other electrons in the base break their covalent bonds and enter the
positive terminal of the battery. Although there is only minority current flow in the reverse-biased junction,
it is still very small because of the limited number of minority current carriers.
