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Transistors
Figure 8.1 How to recognise the location of the base, emitter and collector
connections on a common transistor body
For the previous two chapters, we’ve looked closely at diodes
— the simplest of the group of components known as semiconductors.
The many different types of diodes are all formed
by combining doped layers of semiconductor material at a
junction. The PN junction (as one layer is N-type semiconductor
material and the other layer is P-type) forms the basis of
all other semiconductor-based electronic components. The
transistor — the component we’re going to look at now — is,
in fact, made of two PN junctions, back to back. Figure 8.2
shows how we may simply consider a transistor as being two
back-to-back diodes, and we can verify this using our multimeter
to check resistances between the three terminals of a
transistor: the base, emitter and collector.
To do the experiment, put a transistor into your breadboard,
then use the meter to test the resistance between transistor
terminals. Using our brains here (I know it’s hard) we can
work out that if there are three terminals there must be six
different ways the meter leads can connect to pairs of the
terminals. Table 8.1 lists all six ways, but the results column
is left blank for you to fill in as you perform the experiment.
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