Test: Operating Point of Transistor - Electronics and Communication Engineering (ECE) MCQ

Reverse saturation current is the collector current when emitter is open circuited and base-collector junction is reverse bias mode. In this mode of operation collector-base junction act as a reverse biased diode. The current in this reverse biased junction is known as reverse saturation current.

 Reverse collector current ICBO is collector-base current when emitter is open. This is same as reverse saturation current in ideal but have slight difference in practical.

One of the reasons why reverse collector current exceeds the reverse saturation current is
Introduction of avalanche multiplication current in the base collector junction. This happens when high energy electron collides in the lattice it creates more number of electron and thus a greater current.

One of the reasons why reverse collector current exceeds the reverse saturation current is
Introduction of avalanche multiplication current in the base collector junction. This happens when high energy electron collides in the lattice it creates more number of electron and thus a greater current.
Another reason is leakage current flowing through junction and surface. The ICBO also counts leakage current flowing through junction and surface.

Common base transistor has very low input resistance (20Ω). It also has very high output resistance. Its current gain is less than unity and it has a medium voltage gain.

Common emitter transistor has high output resistance (about 40k). It has low input resistance (about 1k). Current gain is high (20 to few hundreds). Voltage gain is medium.

 common collector configuration has high input impedance and low output impedance. The current gain is high but voltage gain is low.

Since input resistance is low and output resistance is high common base configuration is used as input stage of multistage amplifier. Common emitter configuration is used for audio signal amplification. Common collector is used for impedance matching.

Common base configuration is used as input stage of multistage amplifier. Since voltage gain is high, common emitter configuration is used for audio signal amplification. Common collector is used for impedance matching.

Common base configuration is used as input stage of multistage amplifier. Common emitter configuration is used for audio signal amplification. Since input impedance is high and output impedance is low, common collector is used for impedance matching.