Test: BJTs Device Structures & Physical Operations - Electrical Engineering (EE) MCQ

BJT consists of three semiconductor regions, base region, emitter region and collector region.

 There are two pn junctions, base-emitter junction and collector-emitter junction respectively.

These three are the defined regions in which a BJT operates.

A BJT operates as an amplifiers in active mode and as a switch in cut-off or saturation mode.

 A BJT operates as an amplifiers in active mode and as a switch in cut-off or saturation mode.

 In cut-off mode there is no current flowing through the BJT hence both junctions must be reversed biased else if either of them is forward biased then the current will flow.

 In cut-off mode there is no current flowing through the BJT hence both junctions must be reversed biased else if either of them is forward biased then the current will flow.

The saturation current does not depends upon the volume of the base-emitter junction. Instead it depends upon the area of the cross section of the base-emitter junction in a direction perpendicular to the flow of current.

Collector current depends linearly of the saturation current and exponentially to the ratio of the voltage difference between the base and collector and thermal voltage.

 Most commonly used transistors have a voltage gain of in the range of 50-200. Only some specially designed transistors have a transistor parameter in the range of 1000.

Ic = k Ie (given) and also Ie = (b + 1)/b Ic (standard result). Equating these two results we get k = b/(b + 1).