Part 1: NPN Transistors
transistor is formed by sandwiching a layer of P-type semiconductor
between two layers of N-type semiconductor.
and emitter of the transistor can be connected in series with a
power source and a load, much as a switch would be in a simple electrical
circuit. In this case the switch is operated by a small current
flowing from the emitter to the base (the base current). No current
will flow from the emitter to the collector until a small voltage
(at least 0.7 volts) is applied to the base of the transistor.
from the emitter to the collector (collector current) is much larger
than the base current. The collector current is also proportional
to the base current: that is, as the base current increases, the
collector current increases, until the transistor reaches is maximum
Note that the
emitter is signified by an arrow on the symbol.