transistor biasing are given below. Forward Active: In this bias, the emitter-base junction is forward biased and the collector-base junction is reverse biased. The transistor is in the active mode of operation. In this mode, the transistor functions as an amplifier.
Saturation: Here, the emitter-base junction and collector-base junction are forward biased. The transistor has a very large flow of currents across the junctions. In this mode, transistor is used as a closed switch. Cut-off: In this bias, the emitter-base junction and collector-base junction are reverse biased.
Transistor in this mode acts an open switch. - - - - - - - - Unit electronics and Communication V BC V EC C I B I E I C E – – N N P (a) V EC R E V BC C I C I B I E E – – (b) Figure . NPN transistor in common collector configuration (a) Schematic circuit diagram (b) Circuit symbol . .
Transistor action in the common base mode The operation of an NPN transistor in the common base mode is explained below. The current flow in a common base NPN transistor in the forward active mode is shown in Figure . . C i B1 i B2 I B I E I C n ++ n + P E V EB V CB Electrons Recombination Figure .
Flow of current in a NPN transistor Basically, a BJT can be considered as two p-n junction diodes connected back- to-back. In the forward active bias of the ii) Common-Emitter (CE) configuration In this configuration, the emitter is common to both the input and output circuits as shown in Figure . . The base current I B is the input current and the collector current I C is the output current.
The input signal is applied between emitter and base while the output is measured between collector and emitter. V CE V BE C I C I B I E E – – P N N (a) V CE V BE C I C I B I E E – – (b) Figure .