17

Amplifying circuits

In this chapter we describe how transistors together with a few other components are used to build simple amplifier circuits. The amplifying action of a bipolar junction transistor was described on page 82, but now we look at this more closely.

Transistor characteristics

There are various test circuits that are used to measure the way in which a transistor behaves. The results of one of the more useful of such tests is illustrated opposite. The transistor is set up in the common emitter connection as on page 98 with additions to allow the base current and the collector emitter p.d. to be controlled and with meters to measure the base and collector currents. First look at the lowest curve in the figure. The base current IB

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