Basic Electronics Paper 2, May/June 2015

Question 3

  1. State the rule for biasing a BJT to operate in the active mode.
  2. Draw the circuit diagram dor a BJT transistor connected in common
  3. (a) emitter mode; (b) collector mode; (a) base mode.



 The expected answers were:
(a)        The general rule for turning on a BJT states that the base-emitter junction must be forward-biased and the collector-base junction must be reverse-biased.

For question 3(a), the correct answer is forward bias the emitter-base (NOT EMITTER, as some candidates suggested) junction, and reverse bias the collector base junction. In the case of question 3(b), most candidates correctly gave the illustrations for the common-base and common-emitter configurations (though some could not correctly identify the input and output terminal pairs), only a few could give the common collector configuration.