Application of operational amplifier

Real Life Application of
Operational Amplifier
Ahmad Raza 4/13/17 Electronics II

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Operational Amplifier
The operational amplifier is an extremely efficient and versatile device. Its applications span the
broad electronic industry filling requirements for signal conditioning, special transfer functions,
analog instrumentation, analog computation, and special systems design. The analog assets of
simplicity and precision characterize circuits utilizing operational amplifiers.
There are two type of application.
Linear application:
In linear application of operation amplifier, the output signal is related with the input signal linearly.
some of the linear application of operation amplifier are as follows: -
▪ Adder or summing
▪ Subtractor or difference
▪ Voltage to current convertor
▪ Current to voltage convertor
▪ Instrumentation amplifier
▪ Analog computation
▪ Power amplifier
Nonlinear application:
In nonlinear application, the relation between input and output signals of operational amplifier is
nonlinear. Nonlinear applications of operational amplifier are given below.
▪ Comparator
▪ logarithmic and antilogarithmic amplifier
▪ Multiplier
▪ Divider
▪ Integrator
▪ Differentiator
▪ Rectifier
▪ Pear detector
▪ Clipper
▪ Clamper
▪ Sample and hold circuit

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• Adder or summing:
The summing amplifier is a one kind of circuit and the configuration of this circuit is based upon the standard
inverting op-amp. The name of this circuit suggests the summing amplifier, that is used to combine the
voltage existing on many inputs into a single output voltage.
The term summing amplifier is also named as adder, which is used to add two signal voltages. The circuit of
the voltage adder is so simple to construct and it enables to add many signals together. These kind of
amplifiers is used in a wide range of electronic circuits. For instance, on a precise amplifier you have to add
a small voltage to terminate the offset error of the operational amplifier. An audio mixer is another example to
add the waveforms together from various channels before sending the mixed signal to a recorder. You can
add or change the input or the gain without messing up with the input of the gain. Just recollect that the
circuit of the inverting summing amplifier changes the input signals.
Here are the circuits.
Summing amplifier is a versatile device, used to combine the signals. These amplifiers add the signals
directly or scale them to fit some prearranged combination rule.
• These amplifiers are used in an audio mixer to add different signals with equal gains
• There are various resistors are used at the input of the summing amplifier to give a weighted sum.
This can be used to change a binary number to a voltage in an AC (digital to analog converter)
• This amplifier is used to apply a DC offset voltage with an AC signal voltage. This process can be
done in an LED modulation circuit to maintain the LED in its linear operating range.
Summing Amplifier Based Audio Mixer
The sounds from various musical devices can be changed to an exact voltage level by using transducers,
and linked as input to a summing amplifier. The sounds from various musical devices can be changed to an
Inverting Summing Amplifier Non-inverting Summing Amplifier

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exact voltage level by using transducers, and linked as input to a summing amplifier
Summing Amplifier based DAC:
A DAC converts the binary data which is applied to its input into an analogue voltage value. Digital to analog
conversion is mainly used in Real-time industrial control applications like microcomputers. The o/p of the
microcomputers is digital data that needs to be changed to an analogue voltage to drive the relays,
actuators, motors, etc. The simplest DAC circuit includes a summing amplifier and also a weighted resistor.
The exactness of such a DA (digital to analogue converter) circuit is imperfect by the accuracy of the values
of the resistor employed and the differences in denoting the logic levels.
Summing Amplifier Audio Mixer
These different signal
sources will be added
together by this amplifier,
and the added signal is
directed to an audio
amplifier..The working
principle of the summing
amplifier is like a multi-
channel audio mixer for
several audio channels
Circuit Diagram
Convertor with 4 resistor
Practical Example
Digital to Analog Convertor

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• Adder and Subtractor
Operational amplifier is used to perform addition and subtraction simultaneously.
Here is its circuit diagram.
This is used in different electronics devices where the addition and subtraction is required simultaneously.
• Voltage to Current Converter
Following Figure shows a classic voltage to current (V-to-I) converter. The resistor values can be selected
such that the output current in the load, varies only with the input voltage, VIN, and is independent of the
load. The circuit is widely used in industrial instruments for supplying a 4 to 20 mA signal.
The circuit has its limitations due in part to the requirement that the resistor ratios must be quite accurate to
obtain a near ideal current source

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Voltage to current converter are commonly used for analog system, meter and relays etc.
• Integrator
Operational amplifier can be configured to perform calculus operations such as differentiation and
integration. In an integrating circuit, the output is the integration of the input voltage with respect to time. A
passive integrator is a circuit which does not use any active devices like op-amps or transistors.
An integrator circuit which consists of active devices is called an Active integrator. An active integrator
provides a much lower output resistance and higher output voltage than is possible with a simple RC circuit.
non-inverting voltage to
current converter
Relay
Relay
Analog to Gigital
Analog to Gigital

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The practical integrator is used in
▪ Analog computation
▪ Ramp wave form generator
o Also, known as sweep generator
o Basic building block of cathode ray oscilloscope and analog to digital convertor
o linear current ramp generator is used in television deflection system
▪ ADC (Analog to digital convertor)
▪ Different wave shape circuit
Inverting
Integrator
Noninverting
integrator
Practial
integrator
Summing
integrator

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• Comparator
The Op-amp comparator compares one analogue voltage level with another analogue voltage level,
or some preset reference voltage, VREF and produces an output signal based on this voltage
comparison. In other words, the op-amp voltage comparator compares the magnitudes of two voltage
inputs and determines which is the largest of the two.
Comparators are commonly used in.
• Zero crossing detecting circuits (A zero crossing detector or ZCD is a one type of voltage comparator,
used to detect a sine waveform transition from positive and negative, that coincides when the i/p crosses
the zero-voltage condition.)
Comparator Circuit Inverting coparator
Non inverting comparator Window Comparator

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Zero cross detector circuit
• window detector circuits (A window detector circuit, also called window comparator circuit or dual edge
limit detector circuits is used to determine whether an unknown input is between two precise reference
threshold voltages. It employs two comparators to detect over-voltage or under-voltage)
• Multivibrators
• Time maker generators
• Phase meters
• Schmitt Triggers

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Some important operational amplifier circuits
Here are some circuits that are used as in our daily life electronics appliance
1. Sensitive Intruder Alarm Circuit
In this circuit, apart from the 741 op-amp IC, a Light Dependent Resistor (LDR) is also used. The
main use of the LDR is to sense the presence of a person through his shadow falling on the sensor.
As soon as the shadow falls on it, the resistance of the device begins to increase.
A 555 timer IC is also used to be triggered by a transistor and thus to drive the alarm load.
2. . Transistor Amplifier Circuit-12 Watts
This circuit is very simple and inexpensive. Only one uA741 op-amp and four transistors are required
for the working of this circuit. The op-amp produces the gain required and the transistors are
connected to work as the speaker driver.
The circuit is highly stable and is
also known to produce a
reasonable output of 12 Watts on
a 4 Ohm speaker. Such a simple
but stable circuit as this can
produce a reasonable output of
12W on a 4 Ohm speaker.

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3. Sound Operated Flip Flop
This circuit is used to toggle the output pins status of a flip-flop IC, using a sound. The op-amp used
here is the IC LM324. Two op-amps from the chip are selected and are used to amplify the sound
picked by the condenser microphone.
The third op-amp inside
the IC is used as a level
detector. The flip-flop IC
used here is the IC
CD4027.
4. Active Crossover Circuit
Crossover circuits are of two types, active and passive. Passive crossover circuit uses passive
components only and they are very simple, but they waste a considerable amount of energy and also
induce distortion. Active crossovers do not have the above said draw backs and they are a better
option for HiFi audio systems. Active crossovers split the incoming complex audio signal into to two
bands, a low frequency out and a high frequency out.
These two bands a separately amplified by two power amplifier stages, one tuned to the low
frequency band and the other tuned to high frequency stage respectively (bi-amping).

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5. Preamplifier for Dynamic Microphones
Here is a low noise preamplifier design for dynamic microphones. The circuit is based on the uA739 IC
from Fairchild Semiconductors. uA739 is a dual audio operational amplifier with high gain and excellent
stability. Out of the two op-amps available in the IC, only one is used here. The audio signals from the
microphone are coupled to the non-inverting input of IC1 through the capacitor C1 and resistor R1. C1
performs input DC decoupling. The R1, C2 network bypasses the unwanted high frequency signals from
the microphone.
A fraction of the output is fed back to the inverting input in order to prevent oscillations and ensure better
stability. The input impedance of this circuit is around 50K.This amplifier can handle signal from 20Hz to
20 KHz, which makes it excellent for audio applications.

Application of operational amplifier

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