Classification and Differences of 74 Series Digital Integrated Circuits

74 Series Digital Integrated Circuits can be roughly divided into six main categories:

74×× (Standard type);

74LS×× (Low-power Schottky);

74S×× (Schottky);

74ALS×× (Advanced Low-power Schottky);

74AS×× (Advanced Schottky);

74F×× (Fast).

HC denotes CMOS logic level;
HCT denotes TTL logic level, interchangeable with the 74LS series;

HCU is suitable for CMOS circuits without buffer stages.

These 9 types of 74 Series Digital Integrated Circuits have the same logic function and pin layout as long as the suffix number is the same. Based on different conditions and requirements, one can select different types of 74 Series Digital Integrated Circuits. For example, if the power supply voltage is 3V, the 74HC series is recommended.

74 – Series
This is an early product series that is still in use but is gradually being phased out.

74H – Series
An improved version of the 74 – Series, classified as high-speed TTL products. The average propagation delay for NAND gates is around 10ns, but the static power consumption is relatively high. Usage is decreasing, and the series is being phased out.

74S – Series
This is the high-speed Schottky version of TTL. It uses saturation-resistant Schottky diodes for higher speed but has limited variety.

74LS – Series
This is currently the main product line within TTL types. It has a wide range of models and manufacturers. With a high performance-to-cost ratio, it is widely used in small and medium-scale circuits.

74ALS – Series
This is the “Advanced Low-power Schottky” series and a successor to the 74LS – Series. It shows significant improvements in speed (typical 4ns) and power consumption (typical 1mW), though it is more expensive.

74AS – Series
This is the successor to the 74S – Series, with significant speed improvements (typical 1.5ns), also known as the “Advanced Super High-speed Schottky” series.

74HC – Series
The 54/74HC – Series is a high-speed CMOS standard logic circuit series. It offers the same operating speed as the 74LS – Series, along with the low power consumption and wide power supply range typical of CMOS circuits.
74HCxxx is a direct counterpart to 74LSxxx, with the same model number suffix indicating identical logic functions and pin arrangements, making it easy to replace 74LS with 74HC.

74AC – Series
Also known as “Advanced CMOS Integrated Circuits,” the 54/74AC series offers the same speed as the 74AS series while maintaining the inherent low power and wide voltage range of CMOS technology.

ACT – High-performance CMOS logic gate series (TTL-compatible inputs with buffering)

AC – High-performance CMOS logic gate series (with buffering)

ALS – High-performance low-power logic gate series (TTL-compatible with buffering)

AS – High-performance logic gate series (TTL-compatible with buffering)

C – CMOS logic gate series

FCT – Fast CMOS logic gate series

F – Fast logic gate series (TTL-compatible)

HC-4XX – High-speed CMOS logic gate series (TTL-compatible)

HCT-4XX – High-speed CMOS logic gate series (TTL-compatible)

HCT – High-speed CMOS logic gate series (TTL-compatible)

HC – Logic gate series using CMOS interfaces

LS – Low-power logic gate series (TTL-compatible)

S – High-speed logic gate series (TTL-compatible)

VHCT – TTL-compatible logic gate series with TTL interface