74HC74

Updated: 2026-10-22

Overview

The 74HC74 is a dual positive-edge-triggered D-type flip-flop integrated circuit from the 74HC logic family. Each IC contains two independent flip-flops with individual data (D), clock (CP), set (SD), and reset (RD) inputs, along with complementary outputs (Q and Q̅). As a member of the high-speed CMOS (HC) series, it combines low power consumption with TTL compatibility, making it suitable for interfacing between older TTL systems and modern CMOS circuits. The device operates across a wide voltage range (2V to 6V) and finds extensive use in digital systems for data synchronization and temporary storage applications.

Structure and Working Principle

Each D-type flip-flop in the 74HC74 consists of synchronous data storage elements that transfer the D input's state to the Q output upon receiving a low-to-high clock transition. The set and reset inputs function asynchronously, overriding the clock when activated (active LOW). The internal structure uses CMOS technology with buffered inputs for improved noise immunity. The flip-flops remain transparent while the clock is high in basic configurations, though edge-triggered operation ensures reliable state capture only at the clock's rising edge. This behavior makes the IC particularly useful for clock domain crossing and pipeline implementations in digital designs.

Key Features

The 74HC74 delivers typical propagation delays of 13ns at 5V supply, with a maximum toggle frequency around 77MHz. It features balanced propagation delays between high-to-low and low-to-high transitions for predictable timing. Notably, the IC maintains extremely low static power consumption (under 1μA) when not switching, while dynamic power scales with clock frequency. Inputs include Schmitt-trigger characteristics for improved noise rejection. The outputs can source or sink up to 5.2mA while maintaining voltage compliance with both TTL and CMOS logic standards.

Application Areas

Primary applications include register banks, shift registers, and simple state machines in embedded systems. The 74HC74 serves as a fundamental building block for clock dividers, synchronizers, and debounce circuits. In communication systems, it finds use in data packet framing and signal retiming. Industrial applications include rotary encoder interfaces and process control sequencing. Consumer electronics employ these flip-flops for button debouncing, mode switching logic, and display multiplexing in appliances and digital devices.

Maintenance and Precautions

Proper handling requires ESD protection during installation, as the CMOS inputs can be damaged by static discharge. Designers should include bypass capacitors (0.1μF) near the power pins to prevent noise issues. Operating temperatures typically range from -40°C to +125°C for industrial-grade variants. Input voltages must not exceed the supply rail, and unused inputs should be tied high or low rather than left floating. For hot-plug scenarios, consider series current-limiting resistors on all signal lines.

B2B Procurement Guide

When sourcing 74HC74 ICs, verify production date codes to avoid obsolete versions. Major manufacturers include NXP, Texas Instruments, and ON Semiconductor, each offering slightly different parametric specifications. Industrial buyers should request characterization reports for critical parameters like setup/hold times and clock-to-output delays. Consider alternative packaging (SOIC, TSSOP) for space-constrained applications. MOQ typically starts at 1,000 pieces for competitive pricing, with lead times varying from 4-12 weeks depending on market conditions and packaging options.