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 terminal of a 8 V battery is connected to the collector through a load res

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 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 base-emitter voltage V BE = 0 . 6 V and base current amplification factor β d . c . = 100 . Find the values of R L and R B .

TestHub · Accepted Answer

See figure. Potential difference across $R_{L}$

$I_{c} R_{L} = 8 V - V_{CE}$

$= 8 V - 4 V = 4 V$

Now $I_{C} R_{L} = 4 V$

$R_{L} = \frac{4}{4 \times 10^{- 3}} = 10^{3} Ω = 1 kΩ$

Further, for base-emitter equation,

$V_{CC} = I_{B} R_{B} + V_{BE}$

or $I_{B} R_{B} =$ Potential difference across $R_{B}$

$= V_{CC} - V_{BE} = 8 - 0.6 = 7.4 V$

Again $I_{B} = \frac{I_{C}}{β} = \frac{4 \times 10^{- 3}}{100} = 4 \times 10^{- 5} A$

$R_{B} = \frac{7.4}{4 \times 10^{- 5}} = 1.85 \times 10^{5} Ω = 185 kΩ$

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