7400 Series Guide: 74HC27/74LS27 (Triple 3-input NOR gates)

The 74×27 (ex 74HC27) is a chip with three 3-input NOR gates.

In this guide, you’ll learn the things you need to know about this chip to use these 3-input NOR gates in your projects.

Package and pinout for the 74HC27/74LS27

What does the 74HC27 / 74LS27 do?

The 74×27 gives you three 3-input NOR gates.

A NOR gate is a logic gate that outputs 1 (HIGH) if all of its inputs are 0 (LOW). Therefore, if you input a HIGH in any of the inputs, the output will become LOW. Otherwise, the output will be HIGH.

3-input NOR gate symbol
3-input NOR gate symbol
Input AInput BInput COutput Q
Truth Table for the 3-input NOR gate

How To Use This Chip

The 74HC27 comes in a 14-pin package, and you need to connect it to power before you can use it. Most 7400 ICs support a VCC voltage of 5V. One difference between the HC and LS version of the chip is that the 74HC27 supports 2V to 6V, while the 74LS27 only supports 5V.

The maximum current you can pull out of one output pin is 4 mA when the pin is high (sourcing) or 16 mA when the pin is low (sinking). This can differ between models, so check the datasheet of your model to verify.

Once you’ve connected it to power, you can use any of the three 3-input NOR gates inside.

7400 series IC connected to 5V on a breadboard
The 74HC27/74LS27 IC connected to power

74×27 Pinout

The 74×27 has 14 pins and contains three 3-input NOR gates laid out as shown in the pinout diagram below:

74HC27/74LS27 Pinout
Pin #TypeDescription
1InputInput to the first NOR gate.
2InputInput to the first NOR gate.
3InputInput to the second NOR gate.
4InputInput to the second NOR gate.
5InputInput to the second NOR gate.
6OutputOutput from the second NOR gate.
7PowerConnect to ground (GND).
8OutputOutput from the third NOR gate.
9InputInput to the third NOR gate.
10InputInput to the third NOR gate.
11InputInput to the third NOR gate.
12OutputOutput from the first NOR gate.
13InputInput to the first NOR gate.
14PowerPositive power supply (VCC). Connect to +5V power.
Pin overview for the 74×27 IC

Alternatives and Equivalents for 74HC27 / 74LS27

There are many versions of the 74×27 chip. They all have the same functionality but with different specifications such as supported voltages and maximum current output.

Here’s a list of a few equivalents of this chip:

  • 74HC27 (High-speed CMOS)
  • 74HCT27 (High-speed CMOS, TTL compatible)
  • 74LS27 (High-speed TTL)
  • 74LVC27 (Low Voltage TTL)
  • 74AC27 (Advanced CMOS)
  • 74ALS27 (Advanced Low-Power Schottky TTL)
  • 74F27 (Very High Speed)
  • 74C27 (CMOS, similar to the 4000-series)

Some manufacturers also add a prefix, such as the SN74HC27 and SN74LS27 by Texas Instruments.

Can’t find the 74×27 anywhere? Then try one of the following IC alternatives:

  • CD4075 – Triple 3-input NOR gates

If you can’t find the 74×27 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 74LS27 and 74HC27 chips

Download the PDF datasheet for your version of the 74×27 here:

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