The operational amplifier is one of the most useful electronic components, because of it's ability to compare, add and subtract (voltages), amplifiy (or multiply) voltages, or integrate/differentiate using additional components, such as a capacitor in a circuit with an op – amp.
The operational amplifier has a very high open loop voltage gain – up to
for dc. If ac is used, this gain typically decreases with frequency.It has a very high imput resistanace, drawing close to zero current from the supply, a very low output resistance. It can act as a differential amplifier by multiplying the different between the voltages to the two input termainal, if this different is less than about 150 micro Volts.
A common op – amp is an eight pin dual (type 741) in line form, shown below.
We are interested in only five of the eight pins.
-
The inverting pin 2 above with input voltage
Inputs are changed in sign or polarity. -
The non - inverting pin 3 above with input voltage
Inputs are not changed in sign or polarity. -
The out put pin (6 above).
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The positive supply (7 above).
-
The negative supply (4 above).
We treat the op – amp as an amplifier with an open loop gain
given by