WORKING OF BJT AMPLIFIER

                   

                     Have  your tried to know ,How BJT transistor acts as an amplifier?If you dont know ,Then Don't worry we will explain it to you.

                The first thing everyone needs to know is  ,The voltage applied at the base of the transistor is very small when compared to the collector voltage and  dDC voltage at base should be  of the order of around 0.7 volts                

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                           Second thing you need to know is,the base voltage controls the collector terminal voltage.

                          Next ,the third thing you need to know is ,the small A.C signal is applied at the baseterminal voltage only and the amplified AC signal is taken out at Collector terminal.

From the figure,we can see the notations of the teriminals of a bjt transitor.

                     

     When the voltage of the AC signal applied at the base terminal is increased or Let us take the voltage at the peak then the whole current will flow  from collector to emitter terminal and reach the ground,and the ouput current taken at collector terminal becomes zero.Hence voltage  will appear zero or minimum at collector terminal.let us say it is connected to ground virtually at that time.

                           When the voltage across base terminal decreases  i.e let us take at zero crossing point of the waveform,then the  current from collector to emitter  will decrease  which will increase the voltage at collector  eventually.

                                   " since voltage drop  is directly proportional to current"So voltage drop will be small i.e high voltage from Vcc will appear at collector terminal.Hence the output collector voltage will be high.

                             when the base voltage values are taken at permmisible intervals we can observe the exact replica of the input signal but of the higher values ,since the input Dc voltage at the collector is high i.e of the order of 10 volts.

conclusion :"In other words ,We can say that  the alternating small input signal is controlling the collector terminal voltage and also shaping the  collector terminal High DC voltage to large sinusoidal signal waveform, JUST LIKE POTTERY MAN SHAPING THE POT." 

Here ,we can also say that the phase difference between input signal and output signal is 180 DEGREES ,(which is used in the generation of oscillations to produce completely 360 or 0 degrees phase shift.)