The Operational Amplifier is probably the most versatile Integrated Circuit available. The most common Op-Amp is the 741 and it is used in many circuits, as it is very cheap. Its main purpose is to amplify (increase) a weak signal.
The OP-AMP has two inputs, INVERTING ( - ) and NON-INVERTING (+), and one output at pin 6. The chip can be used in a circuit in two ways. If the voltage goes into pin 2 then it is known as an INVERTING AMPLIFIER (it reverses the polarity of the input signal).
If the voltage goes into pin 3 then the circuit becomes a NON-INVERTING AMPLIFIER, the onj that we are going to build now.
Step 1: Theory of Operation and Simulation
As you may see from the schematic, only a few components are needed to build the circuit.
The circuits accepts as input a small signal, and gives the amplified signal (with same frequency and same polarity of the original) at the output. The gain is controlled by the two resistors R1 and R2, by this simple law:
GAIN (AV) = 1+(R2 / R1)
Example : if R2 is 1000 kilo-ohm and R1 is 100 kilo-ohm the gain would be :
GAIN (AV) = 1+ (1000/100) = 1 + 10 = 11
So if the input voltage is 0.5v the output voltage would be :
0.5 X 11 = 5.5v
Note that you may not amplify the input signal as you want: the output signal is limited by the two IC's power sources: in this case the output signal cannot be greater than +12V.
Also note that the output signal may be altered even if the input signal's frequency and amplitude is too high (try searching for "Slew Rate").
Step 2: UA741 on a Breadboard
To build this circuit you'll need:
1x 1.2KOhm resistor
1x 47KOhm resistor
1x UA741CD OpAmp
1x Function Generator
1x Oscilloscope (even a multimeter would be fine, but you cannot see the waveform)
1x +- 12V Power Source
1x Breadboard (even a small one)
After you assembled the circuit as in the picture, we are ready to see the results of our amplifier!
Step 3: Final Results
As you may see from the picture, the input signal(the one at the top of the oscilloscope) is a Sinewave with 5KHz frequency and 250mV amplitude.
The gain of our amplifier is:
So, the peak output signal,should be:
Vout=0.25V*40= 10 V
The output signal (the one at the bottom of the oscciloscope) is still a Sinewave, with frequency and polarity untouched (the waves' peaks meet each other), but with an amplitude of 10V !
If the input signal is too big, the output sinewave would be distorced, with the maximum peak at 12 V and then a continuous line on the oscilloscope....