7400 Series Guide: 74LS31 Delay Elements

The 74×31 (ex 74LS31) is a chip that has six delay elements. The delays are created as gates and buffers with typical delays of 6ns, 27.5ns, and 46.5ns.

In this guide, you will learn everything you need to know about this chip and how you can use these delay elements in your own projects.

74HC31 / 74LS31 Package And Pinout

What does the 74HC31 / 74LS31 do?

The 74×31 gives you six delay elements. Typical delays are 27.5ns (1,6), 46.5ns (2,5), 6ns (3,4). The logic applied to each element is:

  • Gates 1 and 6: Inverting (Typical delay between 23ns and 32ns)
  • Gates 2 and 5: Non-Inverting (Typical delay between 45ns and 48ns)
  • Buffers 3 and 4: 2-input NAND (Typical delay of 6ns)

How To Use This Chip

The 74LS31 comes in a 16-pin package, and you need to connect it to power before you can use it. It supports a VCC voltage of 5V.

The 27.5ns and 46.5ns delay element outputs can provide an output current of 8mA when low (sinking), and 0.4 mA when high.

While the 6ns delay elements have improved current capability and provide up to 24mA when low (sinking) and 1.2mA when high.

Once you’ve connected it to power, you can use any of the six delay elements inside.

7400 series IC connected to 5V on a breadboard
The 74HC31/74LS31 IC connected to power

74LS31 Pinout

The 74LS31 has 16 pins and contains six delay elements laid out as shown in the pinout diagram below:

74SL31 pinout
Pin NamePin #TypeDescription
1A1InputInput to the first delay element of typically 27.5ns.
/1Y2OutputOutput from the first delay element (inverted).
2A3InputInput to the second delay element of typically 46.5ns.
2Y4OutputOutput from the second delay element.
3A5InputInput 1 to the third delay element of typically 6ns.
3B6InputInput 2 to the third delay element of typically 6ns.
/3Y7OutputOutput from the third delay element (NAND gate).
GND8PowerConnect to ground (GND).
/4Y9OutputOutput from the fourth delay element (NAND gate).
4A10InputInput 1 to the fourth delay element of typically 6ns.
4B11InputInput 2 to the fourth delay element of typically 6ns.
5Y12OutputOutput from the fifth delay element.
5A13InputInput to the fifth delay element of typically 46.5ns.
/6Y14OutputOutput from the sixth delay element (inverted).
6A15InputInput to the sixth delay element of typically 27.5ns.
VCC16PowerPositive power supply (VCC). Connect to +5V power.
Pin overview for the 74LS31 IC

Alternatives and Equivalents for 74LS31

As far as I know, there are no equivalents to the 74LS31, except for the 54LS31 which is the same chip with military grade specs.

If you can’t find the 74LS31 IC in your local electronics store, don’t worry, you’ll most likely find it in one of the stores listed on this page of online stores where you’ll find components and tools for all your electronics projects.

Datasheet for the 74LS31 and 74HC31 chips

Download the PDF datasheet for your version of the 74×31 here:

Leave a Comment