Biasing a transistor
A transistor in a circuit needs the right voltages on its terminals: it must be biased.
Biasing
As an amplifier, the emitter-base junction must be forward biased and the base-collector junction reverse biased by a larger voltage. For an npn transistor, C goes to the positive terminal and E to the negative; the base gets a smaller voltage the same way round as the collector's.
For a pnp transistor it is the other way: E to + and C to −.
Only npn transistors are used in the circuits of the O/L syllabus.
Identifying the leads
There is no general rule for recognising a transistor's leads, and transistors are numbered to tell them apart — for example 2SC828 (C828), 2SD400 (D400), 2SC1061 (C1061), 2SD313 (D313). Data books show the leads as seen from below, pointing towards you. All four are npn silicon transistors.
Figure to be added