The LM358 Dual OP-AMP IC contains two independent op-amps in one package, which helps reduce circuit size and component count. Because it can work from a single power supply and accepts input signals close to ground, it is easier to use in many low-voltage and battery-powered circuits. This article explains the LM358 in a complete but easy-to-understand way. It covers the IC’s pinout, internal structure, features, specifications, working circuits, and more.

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LM358 Dual OP-AMP IC Basic

The LM358 is a dual operational amplifier IC that contains two independent op-amps in one package. It is designed for low power consumption and can operate from a single power supply. The LM358 series also supports a common-mode input voltage range that includes ground, making it easier to use in single-supply circuit designs.

The LM358 can operate at supply voltages as low as 3.0 V and as high as 32 V. It also has low quiescent current compared with older standard op-amp ICs. Its output voltage range includes the negative supply voltage, which helps reduce the need for extra biasing components.

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LM358 Dual OP-AMP IC Pinout Details

Alternatives & Equivalent Model

LM358 Schematic Block Diagram

The LM358 uses a differential input stage formed by transistors Q1 through Q4. This stage compares the voltages applied to the inverting and non-inverting inputs and converts the difference into an internal control signal. The current-source transistors provide stable bias currents that help maintain consistent operation over different supply voltages and temperatures.

The amplified signal from the input stage is then processed by the voltage gain stage, which includes transistors such as Q10 and Q11. This section provides most of the voltage amplification required by the operational amplifier. The compensation capacitor (Cc) is integrated into the design to improve stability and prevent unwanted oscillations during operation.

The output stage consists of transistors Q5, Q6, Q7, and Q13. This stage boosts the current-driving capability of the amplifier and delivers the final output signal to the load. The output can swing close to the ground rail, making the LM358 well suited for single-supply operation.

LM358 Features and Specifications

LM358 Working in Circuit

LM358 Temperature Controller Circuit

In this circuit, the LM358 operates as a voltage comparator for temperature monitoring and control. An NTC thermistor senses temperature changes by varying its resistance. As the temperature increases, the resistance of the NTC decreases, causing the voltage at one LM358 input to change.

A potentiometer provides an adjustable reference voltage to the other input of the LM358. The amplifier continuously compares the thermistor voltage with the reference voltage. When the measured temperature crosses the preset threshold, the LM358 output changes state.

The output drives transistor Q1 through resistor R1. When Q1 turns on, it energizes relay K1, allowing power to be supplied to the heater. Diode D4 protects the transistor from voltage spikes generated by the relay coil. This arrangement enables automatic temperature regulation based on the user-defined setpoint.

LM358 Two-Stage Signal Amplifier Circuit

This circuit uses both operational amplifiers inside the LM358 to provide two stages of signal amplification. The input signal first passes through capacitor C2, which blocks DC components and allows only the AC signal to enter the amplifier.

The first amplifier stage (U1A) amplifies the incoming signal using a feedback network formed by R1 and C1. The amplified output is then passed through potentiometer R5, which allows adjustment of the signal level before it reaches the second stage.

The second amplifier stage (U1B) provides additional amplification and filtering. Components R9 and C3 determine the gain and frequency response of this stage. Capacitor C4 couples the two stages while preventing unwanted DC voltage transfer.

The LED and resistor R10 serve as a power indicator. Together, both LM358 amplifiers increase signal strength, improve conditioning, and provide a controlled output suitable for further analog processing.

Applications of LM358

Sensor Signal Conditioning

The LM358 is used to strengthen weak sensor signals before they are read by controllers, meters, or processing circuits. It is suitable for sensors that produce small voltage changes, such as temperature, light, pressure, and gas sensors.

Voltage Comparison

The LM358 can compare an input voltage with a reference voltage and change its output when the input reaches a set level. This makes it useful for threshold detection, low-battery warning, and protection circuits.

Active Filter Circuits

The LM358 can be used in active filter circuits to separate useful signals from unwanted frequencies. It supports low-pass, high-pass, and band-pass filter designs for audio, measurement, and control systems.

Audio Preamplification

The LM358 can boost low-level audio signals before they enter another amplifier stage. It is commonly used in simple microphone, tone control, and basic audio preamplifier circuits.

Oscillator and Waveform Generation

The LM358 can be configured to generate repeated waveforms such as square waves and triangular waves. These circuits are useful for timing, signal testing, and basic control functions.

Current Sensing

The LM358 can amplify the small voltage across a shunt resistor to help measure current flow. This is useful in battery chargers, motor drivers, power supplies, and load monitoring circuits.

Power Supply Monitoring

The LM358 can monitor supply voltage levels and detect abnormal conditions such as undervoltage or overvoltage. It helps improve circuit safety by triggering alarms, shutdown signals, or control actions.

Temperature Control

The LM358 can work with thermistors or temperature sensors to control heaters, fans, or alarms. It compares the sensed temperature with a set reference voltage and switches the output when the limit is reached.

LM358 vs Other Operational Amplifiers

LM358 Mechanical Dimensions

Manufacturer

ON Semiconductor (onsemi) manufactures the LM358 using mature analog semiconductor fabrication processes optimized for high-volume, cost-effective production. The company supports a wide range of package options, including through-hole and surface-mount variants, to meet the needs of consumer, industrial, automotive, and power-management applications. onsemi's manufacturing capabilities include automated wafer fabrication, assembly, testing, and quality-control procedures that ensure consistent electrical performance and long-term reliability. Through its global production and supply chain network, onsemi can provide LM358 devices in large quantities while maintaining compliance with industry quality and environmental standards.