Op amplifier 741: Features, Pinout, Circuit, and Applications

Introduction to Op Amp IC 741

The Op-Amp IC 741, also known as the LM741, is a widely used operational amplifier integrated circuit. It is designed to perform mathematical operations and amplification functions, such as addition, subtraction, multiplication, division, differentiation, and integration in various circuits.

The IC 741 is a high-gain amplifier composed of BJTs or FETs, typically powered by both positive and negative supply voltages. Initially developed by Fairchild Semiconductor in 1963, it remains a fundamental component in many electronic applications.

In this guide, we will explore the basics, characteristics, circuit configurations, pin layouts, and applications of the Op-Amp IC 741. For further exploration, consider checking out the LM358 Dual Audio Amplifier IC, which includes a pair of Op-Amp circuits.

Characteristics

Key characteristics of the Op-Amp IC 741 include:

• Input Impedance: > 100 KΩ
• Output Impedance: < 100 Ω
• Frequency Range: 0 Hz to 1 MHz
• Low Offset Voltage and Current
• Voltage Gain: Approximately 200,000

Specifications

The primary specifications of the Op-Amp IC 741 are:

• Power Supply: Requires a minimum of 5V, with a maximum of 18V.
• Input Impedance: Around 2 MΩ.
• Output Impedance: Approximately 75 Ω.
• Voltage Gain: 200,000 for a minimal frequency range.
• Slew Rate: 0.5V/µs.
• Input Offset Voltage: Between 2 mV and 6 mV.
• Output Load: Recommended > 2 KΩ.
• Maximum Output Current: 20 mA.

For optimal performance as a voltage amplifier, the IC 741 should have high input impedance and low output impedance. These values make the Op-Amp IC 741 nearly ideal for voltage amplification.

Op Amp IC 741 Pin Configuration

The Op-Amp 741 has an eight-pin configuration. Pins 2, 3, and 6 are the most critical, representing the inverting input, non-inverting input, and output voltage, respectively. Pin 8 is inactive.

The number 741 signifies seven active pins. Pins 2, 3, 4, and 7 are input pins, while pin 6 is the output pin. The IC is often depicted as a triangle, representing the op-amp integrated circuit.

Pin Functions:

• Power Supply Pins (Pin 4 and Pin 7): Provide negative and positive supply voltages, respectively. The voltage range is 5V to 18V.
• Input Pins (Pin 2 and Pin 3): Pin 2 is the inverting input, and pin 3 is the non-inverting input. Voltage at pin 2 higher than pin 3 results in a low output signal and vice versa.
• Output Pin (Pin 6): The output voltage at this pin varies based on the input pins and feedback configuration.
• Offset Null Pins (Pin 1 and Pin 5): Used for offset voltage adjustment to counteract voltage variations.
• Not Connected Pin (Pin 8): Unused in the circuit.

Working & Internal Schematics of Op-Amp IC 741

In the Op-Amp IC 741, the inverting and non-inverting terminals are connected to transistors Q1 and Q2, respectively. Both Q1 and Q2 function as NPN emitters. The outputs of these transistors are connected to transistors Q3 and Q4, which help isolate the inputs and prevent possible feedback.

Voltage fluctuations at the input can affect current flow within the internal circuit, impacting the transistor’s effective functional range. To mitigate this, two current mirrors are used. The transistor pairs Q8 and Q9, and Q12 and Q13, form these mirror circuits.

Q8 and Q12 act as regulating transistors, setting the voltage level at the emitter-base junction for their corresponding pairs. This voltage level is regulated accurately to allow the required current flow. The first mirror circuit (Q8 and Q9) is linked to the input circuit, while the second mirror circuit (Q12 and Q13) is linked to the output circuit. Additionally, the third mirror circuit (Q10 and Q11) functions as a high impedance connection between the input and negative supply, providing a reference voltage without loading the input circuit.

Transistor Q16, along with resistors 4.5KΩ and 7.5KΩ, forms a voltage level shifter circuit. This circuit decreases the voltage level from the amplifier’s input section by Vin before passing it to the next circuit, preventing signal distortion at the output stage.

Transistors Q15, Q19, and Q22 are designed to function as a class A amplifier, while Q14, Q17, and Q20 form the output stage of the Op-Amp IC 741. To balance irregularities at the input phase of the differential circuit, transistors Q5, Q6, and Q7 form a configuration that includes offset null adjustments, balancing both inverting and non-inverting inputs.

Open Loop Configuration

The Op-Amp IC 741 can be used in open loop configurations, operating in either inverting or non-inverting modes.

Inverting Operational Amplifier

In the inverting operational amplifier configuration of the IC 741, pin 2 serves as the input and pin 6 as the output. When you apply a positive input voltage to pin 2, the output at pin 6 becomes negative, and vice versa. This reversal of polarity is why it’s called an inverting amplifier.

The gain is given by:

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

The negative sign indicates reversed polarity.

Non-Inverting Operational Amplifier

In the non-inverting operational amplifier configuration of the IC 741, pin 3 is used as the input and pin 6 as the output. The input voltage applied to pin 3 results in an output at pin 6 with the same polarity. So, a positive input voltage yields a positive output, and a negative input voltage yields a negative output. This direct polarity relationship is why it’s called a non-inverting amplifier.

The gain is given by:

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

When R2 set to zero, the gain is one, making the amplifier a voltage follower.

Applications of Op Amp IC 741

The Op-Amp IC 741 is used in various applications:

• Amplifiers (log, antilog, differential) for signals from DC to high radio frequencies.
• Mathematical operations (addition, subtraction, multiplication, division, differentiation, integration).
• Voltage comparators.
• Oscillators generating sinusoidal, square, and triangular waveforms.
• Pulse Width Modulators (PWM).
• Regulated power supplies.
• Active filters.
• Analog-to-Digital Converters (ADCs) and Digital-to-Analog Converters (DACs).
• Current-to-voltage and voltage-to-current converters.