The 74LS04 is one of the most reliable and widely used ICs in the 7400-series TTL (Transistor-Transistor Logic) logic family, known for its durability and performance in digital systems. As a specific model within the 74LS series, it integrates six independent NOT gates (inverters) that provide clean and accurate signal inversion. This article will discuss the features, specifications, working principles, circuit examples, and practical applications of the 74LS04 Hex Inverter IC.

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What is 74LS04?

The 74LS04 is a high-speed hex inverter IC and a specific model within the 74LS series, which itself belongs to the larger 7400-series TTL (Transistor-Transistor Logic) logic family. This family is widely recognized for its reliability and efficiency in digital electronics. The 74LS04 contains six independent NOT gates, each designed to invert digital signals - converting a HIGH input into a LOW output and vice versa.

Operating on a standard 5V supply, the 74LS04 offers fast switching speeds, low power consumption, and TTL-compatible inputs and outputs, making it ideal for waveform shaping, signal conditioning, and digital system design. It is a fundamental component in circuits requiring signal inversion or timing control.

Available in various package options - PDIP-14 for through-hole use, SOIC-14, and SOP (Narrow Surface Mount Package) for compact layouts - the 74LS04 suits both prototype development and mass production.

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74LS04 Pinout Configuration

74LS04 CAD Models

74LS04 Alternatives and Equivalents

74LS04 Schematic Diagram

The schematic diagram of the 74LS04 shows the internal transistor-transistor logic (TTL) structure of a single inverter gate. It demonstrates how an input signal is inverted to produce an opposite output.

At the input stage, a multi-emitter transistor and resistors (12 kΩ, 1.5 kΩ, and 20 kΩ) form a differential amplifier that senses whether the input voltage represents a logic HIGH or LOW. The diode at the input provides protection and ensures proper biasing.

The middle stage uses transistors and resistors (8 kΩ, 4 kΩ, and 3 kΩ) to amplify and invert the signal. When the input is HIGH, the transistors switch in such a way that the output transistor at the end is turned OFF, producing a HIGH output. Conversely, when the input is LOW, the transistors drive the output transistor ON, pulling the output to LOW.

Finally, the output stage, with a totem-pole configuration (two transistors and a 120 Ω resistor), provides strong sourcing and sinking capability, allowing fast switching and stable logic levels. This entire setup makes the 74LS04 a reliable high-speed inverter used in digital logic circuits.

74LS04 Logic Diagram

The 74LS04 logic diagram shows six independent NOT gates, or inverters, each labeled from 1A to 6A for inputs and 1Y to 6Y for outputs. Each gate performs a logical inversion, meaning it outputs the opposite logic level of its input. When an input signal (A) is high (logic “1”), the corresponding output (Y) becomes low (logic “0”), and when the input is low, the output becomes high.

This configuration allows one chip to handle six separate inversion functions, making it highly useful in digital circuits that require signal conditioning, logic control, or waveform shaping. The simple design and clear logic relationship—Y = ¬A—make the 74LS04 an essential component in many electronic systems for implementing logic negation or signal inversion tasks.