7400 Series Guide: 74HC145/74LS145 (4-to-10 BCD Decoder)

The 74×145 (ex 74LS145) is a chip that features a 4-to-10 line BCD (Binary-Coded Decimal) decoder with open-collector outputs. This allows you to take four binary inputs and decode them into one of ten outputs.

In this guide, you’ll learn the things you need to know about this chip in order to use BCD decoders in your own projects.

What does the 74HC145 / 74LS145 do?

The 74×145 is a BCD to decimal decoder/driver. BCD stands for Binary-Coded Decimal, which means it takes in a 4-bit input that represents a decimal digit from 0 to 9. This type of decoder is sometimes called 1-of-10 decoder, since it turns on one of the ten inputs.

This chip has four inputs and ten outputs. Based on the BCD input, it activates one of the ten outputs. The outputs are open-collector, which makes it possible to drive bigger loads. This makes it useful for selecting one particular line out of ten, like lighting up a light respresenting one of the numbers between 1 and 10.

It’s especially handy in applications like displays, where you need to convert binary numbers into readable decimal numbers.

How To Use This Chip

The 74HC145 comes in a 16-pin package, and you need to connect its power pins 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 74HC145 supports 2V to 6V, while the 74LS145 only supports 5V.

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

The outputs of the 74×145 can sink around 80 milliamps of current. But, these values might differ depending on the chip manufacturer.

Once powered, you can input any binary number between 0 and 9 on the inputs and the corresponding output will activate. If you input an invalid number, all of the outputs will be inactive.

74×145 Pinout

The 74×145 has 16 pins and contains 1-of-10 open-collector inverting decoder/demultiplexer laid out as shown in the pinout diagram below:

Pin Name	Pin #	Type	Description
Y0	1	Output	Open-collector output from the BCD to Decimal decoder (active low).
Y1	2	Output	Open-collector output from the BCD to Decimal decoder (active low).
Y2	3	Output	Open-collector output from the BCD to Decimal decoder (active low).
Y3	4	Output	Open-collector output from the BCD to Decimal decoder (active low).
Y4	5	Output	Open-collector output from the BCD to Decimal decoder (active low).
Y5	6	Output	Open-collector output from the BCD to Decimal decoder (active low).
Y6	7	Output	Open-collector output from the BCD to Decimal decoder (active low).
GND	8	Power	Connect to ground (GND).
Y7	9	Output	Open-collector output from the BCD to Decimal decoder (active low).
Y8	10	Output	Open-collector output from the BCD to Decimal decoder (active low).
Y9	11	Output	Open-collector output from the BCD to Decimal decoder (active low).
S3	12	Input	Most significant bit of the input select lines.
S2	13	Input	Second-highest bit of the input select lines.
S1	14	Input	Second-lowest bit of the input select lines.
S0	15	Input	Least significant bit of the input select lines.
VCC	16	Power	Positive power supply. Connect to +5V power.

Alternatives and Equivalents for 74HC145 / 74LS145

There are many versions of the 74×145 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:

• 74HC145 (High-speed CMOS)
• 74HCT145 (High-speed CMOS, TTL compatible)
• 74LS145 (High-speed TTL)
• 74LVC145 (Low Voltage TTL)
• 74AC145 (Advanced CMOS)
• 74ALS145 (Advanced Low-Power Schottky TTL)
• 74F145 (Very High Speed)
• 74C145 (CMOS, similar to the 4000-series)

Some manufacturers also add a prefix, such as the SN74HC145 and SN74LS145 by Texas Instruments.

Can’t find the 74×145 anywhere? Then try one of the following IC alternatives:

• 74×42 – BCD to decimal decoder.
• 74×47 – BCD to 7-segment decoder/driver.
• 74×138 – 3-to-8 line decoder/demultiplexer.
• 74×139 – Dual 2-to-4 line decoder/demultiplexer.
• 74×154 – 4-to-16 line decoder/demultiplexer.
• CD4028 – BCD to decimal or binary to octal decoder.
• CD4514 – 4-to-16 line decoder/demultiplexer with latches.

If you can’t find the 74×145 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 74LS145 and 74HC145 chips

Download the PDF datasheet for your version of the 74×145 here:

• SN74LS145 (Texas Instruments)
• 74LS145 (Futurlec)