Question

An n-p-n transistor in a common - emitter mode is used as a simple voltage amplifier with a collector current of 4 mA. The positive terminal of a 8 V battery is connected to the collector through a load resistance ` R_L ` and to the base through a resistance ` R_B ` . The collector - emitter voltage ` V_(CE) = 4 V` , the base - emitter voltage ` V_(BE) = 0.6 V` and the current amplification factor ` beta = 100 ` . Calculate the values of ` R_L ` and `R_B` .

Answer 1

Potential difference across `R_(L)`
=`8V - V_(CE) = 8V -4V = 4V`
Now `I_(C)R_(L) =4V`
`R_(L)=(4)/(4 xx10^(-3)) =10^(3) Omega = 1k Omega`
Further for base emitter equation
`V_(C C) = I_(B) R_(B) + V_(BE)`
or `I_(B) R_(B)` = Potential difference across`R_(B)`
`= V_(C C) - V_(BE) = 8,-0.6 = 7.4 V`
Again, `I_(B)=(I_(C))/(beta) =(4 xx 10^(-3))/(100) = 4 xx 10^(-5) A`
`:. R_(B)=(7.4)/(4 xx 10^(-5)) = 1.85 xx 10^(5)Omega = 185 k Omega`.