Test: BJTs Current-Voltage Characteristics - Electrical Engineering (EE) MCQ

The natural logarithm of the collector current depends directly on the the potential difference between the base and the emitter.

The collector current depends directly on the saturation current.

kT/q is the correct mathematical expression for the thermal voltage.

Only expression α = ß/ß + 1 is the correct expression that relates α and ß.

Ie = Ic/α or Ic = α Ie

Thermal voltage is given by kT/q which at T = 25 degrees Celsius is approximately 25 mV.

The correct mathematical expression are Ie = (1 – ß) Ib and Ib = (1 – α) Ie respectively.

 At a given value of vBE, increasing vCE increases the reverse-bias voltage on the collector–base junction, and thus increases the width of the depletion region of this junction. This in turn results in a decrease in the effective base width W. Also the saturation current is inversely proportional to the width, the saturation current will increase and also makes collector current increases proportionally. This is the Early Effect. For the reasons mentioned above, it is also known as the base-width modulation effect.

The BJT operates in active mode when the collector-Base junction is reversed bias. Also doping cannot prevent saturation of the transistor.

 Ic = Is exp (Vbe/Vt) – Isc exp(Vbc/Vt). In this expression put ic = 0 and simplify.