Semiconductor Fundamentals Unit 6 – Transistor Load Lines and Gain
UNIT 6 – TRANSISTOR LOAD LINES AND GAIN
UNIT OBJECTIVE
At the completion of this unit, you will be able to demonstrate how operating conditions and gain
affect transistor circuit currents by using a transistor dc or load line.
UNIT FUNDAMENTALS
A transistor is a current-controlling device. A small base current (IB)controls a large collector
current (IC).The collector current equals the emitter current minus the base current: IC = IE - IB.
The base-emitter junction must be forward biased for base current to flow. When the base-
emitter volt-age (VBE) is in the range of0.5 Vdc to 0.75 Vdc, the base current (IB) starts to
increase very rapidly with small increases in VBE.When the base-emitter junction is forward
biased and the base-collector junction is reverse biased, the collector current (IC) is proportional
to the base current (IB).The ratio of the collector current (IC) to the base current (IB) is the
current gain (βDC).The current gain (βDC) for a transistor can be in the range from50 to 300.