HOW TO AMPLIFY ELECTRIC CURRENT :-

WHAT IS AN AMPLIFIER?

An Amplifier is a device that can increase or decrease a signal.We can make an amplifier with a TRANSISTOR. A Transistor operated in CE mode can be useful for the purpose.

  

TRANSISTOR : Transistors are of two types- 1.npn & 2. pnp. Transistors are made imposing impurity to pure semiconductor.If we can impose p-type impurity from both sides to a n-type semiconductor we get a pnp type transistor ; and if we can impose n-type impurity from both side to a p-type semiconductor we get a npn  transistor.

  

 OPERATION of a TRANSISTOR : There are three modes of operations of a transistor :1.CE 2.CB 3.CC. To make an Amplifier we use CE mode operation.The circuit configuration is shown below :

Here we have two types of important characteristics of which output characteristic is needed for Amplifier.

OUTPUT CHARACTERISTICS :

    The output characteristic is the graphical representation of Collector current (Ic) Vs Collector-Emitter Voltage (Vce) keeping the input current (The Base current) fixed or constant.The following figure shows such a characteristic :

    The black st. line AB is called a load line .Using the biasing of the load line we prepare an Amplifier.The colored lines represent different input currents.If a small AC signal is fed to input bias then it slightly changes the input current as a result output current also changes.Input current is of the order micro-Ampere but the output current is of the order of milli-Ampere 1000 times of the input.So if take out put we get Amplified current that was fed to the input.