An npn transistor in a common emitter mode is used as a simple voltage – amplifier with a collector current of 4 mA. The terminal of 8 V battery is connected to the collector through a load resistance $R_{L}$ and base through load resistance $R_{B}$ . The collector emitter voltage $V_{C E} = 4 V$ , base emitter voltage $V_{B E} = 0.6 V$ and current amplification factor $β$ = 100. Find $R_{B}$ (in ohm).

Question

Infinity Learn · Accepted Answer

$$Ic=4mA=4$$×$$10$$−$$3A$$, $$Vcc=8V$$, $$VCE=4V$$, $$VBE=0.6V$$, β$$=100$$, $$RB=$$?Using KVL in outer loop ,  $$Vcc-VBE$$ $$-IbRB$$ $$=$$ $$0$$, ⇒$$RB=Vcc$$−VBEIb,Also , β$$=IcIb$$, ⇒$$Ib=Ic$$β,∴$$RB=Vcc$$−VBEIcβ$$=$$βVCC−$$VBEIc=100(8$$−$$0.64$$×$$10$$−$$3)=25(7.410$$−$$3)=25$$×$$7.4$$×$$103=25$$×$$74$$×$$102=1850$$×$$102=18.50$$×$$104$$Ω

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