7400 Series Guide: 74HC03/74LS03 (NAND gates)

The 74×03 (ex 74HC03) is a chip that’s got four open-collector NAND gates. This type of output makes it simple to connect it to other chips that use different logic levels. However, it also means you can’t just swap it out with a regular NAND gate chip.

In this guide, you’ll learn everything you need to know about the 74HC03 and how you can use its NAND gates in your own circuit.

Chip package and pinout for the 74HC03/74LS03
74HC03 chip and pinout

What does the 74HC03 / 74LS03 do?

The 74×03 gives you four open-collector NAND gates that can be used individually. A NAND gate is a logic gate that outputs 0 (LOW) only if all of its inputs are 1 (HIGH). In the truth table below, you can see what the output will be for any given input:

NAND truth table
Truth table for the NAND gate

How To Use This Chip

The 74HC03 comes in a 14-pin package and needs to be hooked up to power before you can use it. Most 7400 ICs like this one support 5 volts. But there’s a difference between the HC and LS version – the 74HC03 can handle 2 to 6 volts, while the 74LS03 can only do 5 volts.

Once you’ve connected the VCC and GND pins to power, you can use any of the four open-collector NAND gates inside.

7400 series IC connected to 5V on a breadboard
The 74HC03/74LS03 IC connected to power

This chip uses open-collector outputs which means you can only sink current, not source it.

The output of each gate in the 74HC03 can sink around 4 milliamps when it’s powered with 5 volts. On the other hand, the 74LS03 can usually handle about 8 milliamps of current. But, these values might differ depending on the chip manufacturer.

How To Use Open-Collector Outputs

The outputs from the 74HC03 are not your normal high/low outputs. Instead, they use something called open-collector. Open-collector outputs are outputs that are connected via a transistor. And the collector of the transistor is available at the pin. For a NAND gate, it will look like this:

An open-collector NAND gate inside the 74HC03

So when the output from the NAND gate is ‘1’, it turns on the transistor that is connected to the output. When the output from the NAND gate is ‘0’, it means the transistor will be off.

Note: Some chips use MOSFET transistors instead of BJT. In that case, this technique is called open-drain instead, but the concept is exactly the same.

To turn on an LED when the NAND gate output is ‘1’, you must connect the LED from your positive supply, via a resistor, to the open-collector output:

Controlling an LED from an open-collector NAND gate output

If you instead want to get your standard high/low output, you can get this by connecting a resistor from the output up to your positive supply. Then your NAND gate output pin becomes a standard high/low output.

The advantage of using open-collector outputs is that you can choose your HIGH voltage level to make it compatible with whatever the voltage is of the next stage. The resistor acts as a pull-up resistor and makes the HIGH level approximately the same as the VCC voltage that you provide.

Connect a pull-up resistor to use the open-collector NAND gate output as a standard (inverted) high/low output

It’s important to notice that the output will be inverted: A logical HIGH from the NAND gate turns the transistor ON so that the output voltage on the pin becomes low. A logical LOW leaves the transistor OFF so that the output voltage on the pin becomes HIGH.

74×03 Pinout

The 74×03 has 14 pins and contains four open-collector NAND gates laid out as shown in the pinout diagram below. Each gate has the open-collector symbol, reminding you of the type of output:

Pinout for the 74HC03/74LS03 chip
Pin #TypeDescription
1InputInput to the first NAND gate.
2InputInput to the first NAND gate.
3OutputOpen-collector output from the first NAND gate.
4InputInput to the second NAND gate.
5InputInput to the second NAND gate.
6OutputOpen-collector output from the second NAND gate.
7PowerConnect to ground (GND).
8OutputOpen-collector output from the third NAND gate.
9InputInput to the third NAND gate.
10InputInput to the third NAND gate.
11OutputOpen-collector output from the fourth NAND gate.
12InputInput to the fourth NAND gate.
13InputInput to the fourth NAND gate.
14PowerPositive power supply (VCC). Connect to +5V power.
Pin overview for the 74×03 IC

74HC03 Circuit Example: Level Shifter

Here’s a simple example circuit that illustrates how to build a 5V to 3.3V level shifter from a logic NAND gate in the 74HC03 IC. This way you can, for example, connect an Arduino with 5V outputs to an ESP32 microcontroller that only supports 3.3V inputs:

74HC03 level shifter circuit example

To build this circuit, you’ll need the following parts:

  • IC: 74HC03
  • Resistor: 10 kΩ

Alternatives and Equivalents for 74HC03 / 74LS03

There are many versions of the 74×03 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:

  • 74HC03 (High-speed CMOS)
  • 74HCT03 (High-speed CMOS, TTL compatible)
  • 74LS03 (High-speed TTL)
  • 74LVC03 (Low Voltage TTL)
  • 74AC03 (Advanced CMOS)
  • 74ALS03 (Advanced Low-Power Schottky TTL)
  • 74F03 (Very High Speed)
  • 74C03 (CMOS, similar to the 4000-series)

Some manufacturers also add a prefix, such as the SN74HC03 and SN74LS03 by Texas Instruments.

Can’t find the 74×03 anywhere? Then try one of the following IC alternatives:

  • 74×00 – Quad 2-input NAND gates.
  • 74×132 – Quad 2-input NAND gates (with Schmitt-trigger inputs).
  • CD4011 – Quad 2-input NAND gates.
  • CD4093 – Quad 2-input NAND gates (with Schmitt-trigger inputs).

If you can’t find the 74×03 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 74LS03 and 74HC03 chips

Download the PDF datasheet for your version of the 74×03 here:

4 thoughts on “7400 Series Guide: 74HC03/74LS03 (NAND gates)”

  1. For the output of a 74HC03/74LS03 IC does it always use the collector side of a NPN transistor or can it use a PNP transistor ?

  2. What’s the difference between the 7403 and 7401 , they’re both quad 2 input NAND gates with open collector outputs.


Leave a Comment