Op Amp IC 741 Basics, Characteristics, Pins & Applications

Introduction to Op Amp IC 741

Op-Amp IC 741 or LM741 is one of the most used operational amplifier integrated circuits that perform both mathematical operations and amplification functions. This small chip mainly performs mathematical operations like addition, subtraction, multiplication, division, differentiation, integration, etc. in various circuits.

It is a high gain amplifier made up of BJT or FETS, which is often powered by both positive and negative supply voltage. It was first designed by Fairchild Semiconductor in the year 1963.

In this guide, we will learn about the Operational Amplifier IC or Op-Amp 741 or LM741 basics, characteristics, circuits, pins configuration & Applications. You can also check the LM358 Dual Audio Amplifier IC which has a pair of Op-Amp Circuit.

Characteristics

Followings are the main characteristics of Op-Amp IC 741:

Input impedance is more than 100KΩ.
Output impedance is less than 100Ω.
The frequency range is between 0HZ to 1MZ.
Low offset voltage and current.
Voltage gain is about 2,00,000.

Specifications

The followings are the main specifications of op-amp IC 741:

Power Supply: For proper functionality, it requires a minimum supply of 5V and can handle up to 18V.
Input Impedance: About 2 MΩ.
Output Impedance: About 75 Ω.
Voltage Gain: 2,00,000 for a minimal range of frequency.
Slew Rate (Rate at which op-amp can detect voltage change) : 0.5V/µs.
Input offset: In a range of 2mV-6mV.
Output Load: Recommended greater than 2KΩ.
Maximum Output Current: 20 mA.

Note: For the operational amplifier to function as a voltage amplifier, high input impedance and low output impedance values are recommended. This impedance makes op-amp IC 741 a near-ideal voltage amplifier. The above-mentioned specifications are generic and may vary as per the manufacturer.

Op Amp IC 741 Pin Configuration

The symbol and pin configuration of op-amp 741 is shown below. The diagram comprises eight pins. Among these, pins 2,3, and 6 are the most significant pins, where pins 2 and 3 represent inverting and non-inverting terminals respectively, and pin 6 represents output voltage. Pin 8 is inactive in the circuit.

The number 741 in the name indicates that there are 7 active pins, 4 pins (pin 2,3,4,7) are capable of taking input and 1 pin ( pin 6) is an output pin. The triangular form in the IC represents an op-amp integrated circuit.

The functionality of each pin is as follows:

Power Supply Pins (Pin 4 and Pin 7):

Pin 4 and Pin 7 are negative and positive voltage supply terminals respectively. The power required for IC to operate is received from both these pins. The voltage level between these pins can be in the range of 5V to 18V.

Input Pins (Pin 2 and Pin 3):

Pin 2 and pin 3 are input pins for the op-amp IC. Pin 2 is considered as inverting input and pin 3 is considered as non-inverting input. When the voltage at pin 2 is greater than the voltage at pin 3, i.e. the voltage at inverting input is higher, then the output signal is low. Similarly, when the voltage at pin 3 is greater than the voltage at pin 2, i.e. the voltage at the non-inverting input is higher, then the output signal is high.

Output Pin (Pin 6):

Pin 6 is the output pin of op-amp IC 741. The output voltage at this pin depends on the voltage level on input pins and the feedback approach used. When the voltage at this pin is high, this means that the output voltage is similar to the positive supply voltage. Similarly, when the voltage at this pin is low, this means that the output voltage is similar to the negative output voltage.

Offset Null Pin (Pin 1 and Pin 5):

Pin 1 and pin 5 are used for offset voltage in op-amp IC 741. Because of the higher voltage gain of op-amp IC 741, even minimal variation of voltage at inverting and non-inverting inputs caused due to abnormalities in construction procedure or other external disturbances can influence the output voltage. To overcome this effect, an offset value of voltage can be applied at pin 1 and pin 5, and this is generally done by using a potentiometer.

Not Connected Pin (Pin 8):

Pin 8 is not connected to any circuit inside op-amp IC 741. It is just a pin used to fill the void space in 8-pin standard packages.

Working & Internal Schematics Op-Amp IC 741

A standard op-amp IC 741 is constructed with a circuit containing 20 transistors and 11 resistors. All these transistors and resistors are integrated into a single monolithic chip. The internal connections of these components are illustrated in the figure shown below.

Here, inverting and non-inverting terminals are connected to transistors Q1 and Q2 respectively. Both transistors Q1 and Q2 function as NPN emitters. The output of transistors Q1 and Q2 are connected to a couple of Q3 and Q4 transistors. This type of configuration isolates both inputs to the transistors Q3 & Q4 and prevents possible feedback which might take place.

The voltage fluctuation at the input of op-amp can impact current flow in the internal circuit and also impact the effective functional range of the transistor in the circuit. To prevent from happening this, two current mirrors are used. The transistor pair (Q8, Q9) and (Q12, Q13) are connected in a way to form two mirror circuits.

Transistors Q8 and Q12 are used as regulating transistors which sets the voltage level at the emitter-base (EB) junction for the corresponding pair of transistors. This voltage level can be regulated accurately to some decimal of millivolts in order to allow the required amount of current flow.

The first mirror circuit developed by Q8 and Q9 is coupled to the input circuit and the second mirror circuit developed by Q12 and Q13 is coupled to the output circuit. Also, the third mirror circuit developed by Q10and Q11 function as a high impedance connection between input and negative supply. It provides the reference voltage showing no loading effect on the input circuit.

The transistor Q16 along with resistors 4.5KΩ and 7.5KΩ form a voltage level shifter circuit which decreases the voltage level from the amplifier circuit at the input section by Vin before it gets passed to the next circuit. This is done to prevent signal distortion at the output amplifier section.

Transistors Q15, Q19, and Q22 are designed to function as class A amplifier, and the transistors Q14, Q17, and Q20 form the output stage of the operational amplifier IC 741.

In order to balance any irregularities at the input phase of the differential circuit, transistors Q5, Q6, and Q7 are to form a configuration that has Offset null +ve and –ve and balances both the inverting and non-inverting inputs correspondingly.

Open Loop Configuration

The simplest approach for implementing operational amplifier IC 741 is to operate it on an open loop configuration. The open loop configuration is in inverting and non-inverting modes.

Inverting Operational Amplifier

In inverting operational amplifier IC 741, Pin 2 and pin 6 are used as input and output pins. The input voltage is given through pin 2 and output is taken from pin 6 resulting in reversal polarity. When the input voltage is positive, the output will be negative and when the input voltage is negative, the output will be positive. Hence the amplifier is named as inverting amplifier.

The circuit diagram and Input Output waveform for inverting the operational amplifier are shown in the figure below.

The Gain of the inverting Amplifier is given by the formula:

Gain (Av) = -(R2/R1) ; where, R2 is feedback resistor

Use the Op-Amp Gain Calculator to calculate the Op-Amp Gain.

Here, the Negative sign indicates that the polarity of the output voltage is reversed. By adjusting the value of R1 and R2, desired amplification can be achieved.

Non-inverting Operational Amplifier

In the Non-inverting operational amplifier IC 741, Pin 3 and pin 6 are used as input and output pins. The input voltage is given through pin 3 and output is taken from pin 6 retaining the same polarity as in input voltage. When the input voltage is positive, the output will be positive and when the input voltage is negative, the output will also be negative. Hence the amplifier is named a non-inverting amplifier.

The circuit diagram and Input Output waveform for inverting the operational amplifier is shown in the figure below.

The Gain of the non-inverting amplifier is given by the formula

Gain (Av) = 1 + (R2/R1) ; where, R2 is feedback resistor

By adjusting the value of R1 and R2, desired amplification can be achieved. When the feedback resistor R2 is Zero, The gain comes out one and the operational amplifier behaves as a Voltage follower or unity gain buffer.

Applications of Op Amp IC 741

There are many electronics circuits designed by using an op-amp IC 741. Some of the important applications of op-amp IC 741 are given below.

It is used in various amplifiers like log and antilog amplifiers, differential amplifiers, etc. to amplify signals of varying frequencies ranging from DC to higher radio frequencies.
It is used to compute various mathematical operations like addition, subtraction, division, multiplication, differentiation, integration, etc.
It is used in voltage comparators to compare voltage signals.
It is used in oscillators to generate different waveforms like sinusoidal, square, triangular, etc. It is also used in Pulse Width Modulators (PWM generators).
It is used in regulated power supply.
It is used in an active filter.
It is used in ADCs and DACs to create converters that convert analog signals to binary forms and binary forms to analog signals.
It is used to convert current to voltage and voltage to current.