Transistors are widely used in switching operations. In the Fig, NPN transistor is connected in common emitter configuration and a resistor RB is connected in series with the base. The load resistance Rc is connected in series with the collector.
Transistor as a switch
Transistors are widely used in switching operations. In the Fig, NPN
transistor is connected in common emitter configuration and a resistor RB
is connected in series with the base. The load resistance Rc is connected in
series with the collector. A pulse type waveform is applied as the input to the
transistor through RB. When the input is high, base emitter junction
is forward biased and current flows through RB into the base. The
values of RB and RC are chosen in such a manner that that the base current
flowing, is enough to saturate the transistor. When the transistor is
saturated, it is said to be ON (maximum current). When the input is low (i.e.)
at 0 V, the base emitter junction is not forward biased. So, no base current
flows. Hence the transistor is said to be OFF.
Transistor circuit configurations
There are three types of circuit
connections (called configurations or modes) for operating a transistor. They
are (i) common base (CB) mode (ii) common emitter (CE) mode and (iii) common
collector (CC) mode.
Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail
11th 12th std standard Class Physics sciense Higher secondary school College Notes : Transistor as a switch |