is in cut off region. As a result, the collector current is zero and correspondingly the voltage drop across R C also becomes nearly zero. The output voltage is high and is equal to V CC . It means that the no current flows through the transistor and it is said to be switched off.
The transistor acts as an open switch. kΩ kΩ V R B V i R C E C V R V i k Ω µ V BE = 0V V R C CC C V k mA Ω V CE = 0V β µ C mA . . Operating Point The operating point is a point where the transistor can be operated efficiently.
A straight line drawn by joining the points A ( V CC , ) and B ( , V CC / R C ) is called the DC load line. The DC load line superimposed on the output characteristics of a transistor is used to learn the concept of operating point of the transistor as shown in Figure . . V CE V CE V CC P Q I C I C = R C V CC I = μA I = μA I = μA I = μA I = DC load line (mA) (V) R Figure .
Output characteristics of a transistor in common emitter mode with the DC load line In Figure . , the points P, Q, R are called Q points or quiescent points - - - - - - - - Unit electronics and Communication We know that β = I C (or) I C = βI B = × μA = μA = mA V V I R CE CC C C mA k = 10V (mA) (V) B ( , 5mA) A (25V, ) Q I C V CE . . Transistor as an amplifier A transistor operating in