___________________________________________________________________________ Transistors
terminal of the battery. This movement of electrons into the base and out of the emitter
constitutes base current flow (IB) and the path these electrons take is referred to as the
emitter-base circuit.
Figure 2-11. Forward-biased Junction in a PNP Transistor
2-29. PNP REVERSE-BIASED JUNCTION - In the reverse-biased junction (see Figure
2-12), 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. Electrons that flow from
the negative terminal of the battery fill the holes in the collector. 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 due to the limited
number of minority current carriers.
Figure 2-12. Reversed-biased Junction in a PNP Transistor
23 June 2005
TC 9-62
2-11
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