darlington pair amplifier experiment lab manual

Where is the efficiency, P out is the power output and P s is the power drawn from the power supply.

The input signal to an amplifier will be a current or voltage and the output will be an amplified version of the input signal.

Transistors amplifiers are commonly used in applications like RF (radio frequency), audio, OFC (optic fibre communication) etc.

Anyway the most common application we see in our day to day life is the usage of transistor as an audio amplifier.

As you know there are three transistor configurations that are used commonly i.e.

In common base configuration has a gain less than unity and common collector configuration (emitter follower) has a gain almost equal to unity).

Common emitter follower has a gain that is positive and greater than unity.

So, common emitter configuration is most commonly used in audio amplifier applications.

Input impedance: Input impedance is the impedance seen by the input voltage source when it is connected to the input of the transistor amplifier.

In order to prevent the transistor amplifier circuit from loading the input voltage source, the transistor amplifier circuit must have high input impedance.

Usually the bandwidth is measured based on the half power points i.e.

Vs output graph.

In simple words, bandwidth is the difference between the lower and upper half power points.

The band width of a good audio amplifier must be from 20 Hz to 20 KHz because that is the frequency range that is audible to the human ear.

The frequency response of a single stage RC coupled transistor is shown in the figure below (Fig 3).

Points tagged P1 and P2 are the lower and upper half power points respectively.

It represents how much an amplifier can amplify a given signal.

In decibel the gain is expressed by the equation Gain in dB 10 log (P out P in ).

Gain can be also expressed in terms of output voltage input voltage or output current input current.

Voltage gain in decibel can be expressed using the equation, Av in dB 20 log ( V out V in ) and current gain in dB can be expressed using the equation Ai 20 log (I out I in ).

Where V out is the output voltage V in is the input voltage, Pout is the output power, P in is the input power, R in is the input voltage and R out is the output resistance.

Substituting this in equation 1 we have G 10log ( V out R out ) (V in R in ).(2).

In simple words it is a measure of how much power from the power supply is usefully converted to the output.

Efficiency is usually expressed in percentage and the equation is (P out P s ) x 100.

Darlington Pair Amplifier Experiment Lab Manual