OPAMP
The operational amplifier is arguably the most useful single device in analog electronic circuitry. With only a handful of external components, it can be made to perform a wide variety of analog signal processing tasks. It is also quite affordable, most general-purpose amplifiers selling for under a dollar apiece. Modern designs have been engineered with durability in mind as well: several "op-amps" are manufactured that can sustain direct short-circuits on their outputs without damage.
The Operational Amplifier is probably the most versatile Integrated Circuit available. It is very cheap especially keeping in mind the fact that it contains several hundred components. The most common Op-Amp is the 741 and it is used in many circuits.
The OP AMP is a ‘Linear Amplifier’ with an amazing variety of uses. Its main purpose is to amplify (increase) a weak signal - a little like a Darlington Pair.
The OP-AMP has two inputs, INVERTING ( - ) and NON-INVERTING (+), and one output.
Working in 2 ways
1. An inverting amplifier. Leg two is the input and the output is always reversed.
In an inverting amplifier the voltage enters the 741 chip through leg two and comes out of the 741 chip at leg six.If the polarity is positive going into the chip, it negative by the time it comes out through leg six.The polarity has been ‘inverted’.
GAIN (AV) = -R2 / R1
2. A non-inverting amplifier. Leg three is the input and the output is not reversed.
In a non-inverting amplifier the voltage enters the 741 chip through leg three and leaves the 741 chip through leg six. This time if it is positive going into the 741 then it is still positive coming out. Polarity remains the same.
GAIN (AV) = 1+(R2 / R1)
OPAMP AS COMPARATOR
However, this time the 741 is used as a comparator and not an amplifier. The difference between the two is small but significant. Even if used as a comparator the 741 still detects weak signals so that they can be recognised more easily. It is important to understand these circuits as they very regularly appear in examinations.
A ‘comparator’ is an circuit that compares two input voltages. One voltage is called the reference voltage (Vref) and the other is called the input voltage (Vin).When Vin rises above or falls below Vref the output changes polarity (+ becomes -).
Positive is sometimes called HIGH. Negative is sometimes called LOW
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