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 Electronics Paper 2, Nov/Dec. 2009
 Questions: 1 2 3 4 5 6 7 8 9 10 Main
Weakness/Remedies
Strength

Question 1

State the relationship between common base current gain (a) and common emitter current gain (β) for a bipolar junction transistor.

• In Figure 4, calculate
• IB;
• IC;
• VCE.
_____________________________________________________________________________________________________
OBSERVATION

• For a bipolar junction transistor

β  =      α
1  - α

α  =       β
1+ β
Given that    VBE = 0.6V
α= 0.98
VCC = IBRB + VBE +IERE
VCC = VCE + IcRC + IERE

β  =      α
1  - α
=
=   49

= 25.9µA
=  26µA

VCE = VCC - ICRC -ICRE
= VCC –IC(RC+RE)
= 12 – 1.27mA(5.6K + 1K)
VCE = 3.62V
IC = βIB = 49 x 25.9µA = 1.27µA

The question was on establishing the d.c. (operating point) parameters of a BJT connected in the common-emitter mode. It was quite popular with the candidates. However, the performance was about average.