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Electronics Engineering Objective Questions { Bipolar Junction Transistor }

211. The neutral base width of a bipolar transistor, biased in the active region, is 0.5 gm. The maximum electron concentration and the diffusion constant in the base are I014/cm3 and Dn = 25 cm2/sec respectively. Assuming negligible recombination in the base, the collector current density is (the electron charge is 1.6 x 10-19 coulomb)
A. 800 A/cm2
B. 8 A/cm2
C. 200 A/cm2
D. 2 A/cm2
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212. A bipolar transistor is operating in the active region with a collector current of I mA. Assuming that the 13 of the transistor is 100 and the thermal voltage (VT) is 25 mV, the transconductance (gm) and the input resistance (rx) of the transistor in the common emitter configuration, are
A. gm = 25 mA/V and ric = 15.625 Ic.Q
B. gm = 40 inAN and r 4.0 k.C2
C. gm = 25 mAN and rn = 2.5 kg2
D. gm = 40 mAN and r, = 2.5 Id/
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213. The phenomenon known as "Early Effect" in a bipolar transistor refers to a reduction of the effective base width caused by
A. electron-hole recombination at the base
B. the reverse biasing of the base-collector junction
C. the forward biasing of emitter-base junction
D. the early removal of stored base charge during saturation-to-cutoff switching
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214. The DC current gain (P) of a BJT is 50. Assuming that the emitter injection efficiency is 0.995, the base transport factor is
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215. For the BJT circuit shown, assume that the of the transistor is very large and VBE = 0.7 V. The mode of operation of the BJT is
A. cut-off
B. saturation
C. normal active
D. reverse active
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