GATE 2017 EE (EE2) – Question 47

Analog and Digital Electronics · Amplifiers: biasing, equivalent circuit and frequency response · 2 marks · Multiple choice

In the transistor circuit, $V_{CE}=V_{CC}/2$, $V_{CC}=10$ V, β=29 and forward $V_{BE}=0.7$ V. Find $R_B/R$.

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Correct answer: (D) 129

Explanation

The collector resistor carries both collector and base currents because RB is connected from collector to base. Its current is therefore IE, the same current as through the emitter resistor R.

The voltage equation is $10=4RI_E+5+RI_E$, giving IE R=1 V. Since IE=(β+1)IB=30IB, it follows that IB R=1/30 V.

The base resistor voltage is VC−VB=VCE−VBE=4.3 V. Thus RB/R=4.3/(1/30)=**129, D**.

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