7400 Series Guide: 74LS57 (Frequency Dividers)

The 74×57 (ex 74LS57) is a frequency divider chip that can generate one second timing pulses from 60 Hz (United Stated standard frequency). See the 74LS56 for the same divider aimed at the European frequency of 50 Hz.

Learn how it works and how to use it with this beginner-friendly guide and start using frequency dividers in your projects!

What does the 74LS57 do?

The 74×57 has three frequency dividers on the inside: A, B, and C.

A divides by 6. B divides by 5 and is internally tied to C which divides by 2. That means the output from counter C is 10-to-1 so that it can generate 1-second timing pulses from 60 Hz.

This is very useful if you want to get 1-second pulses using the the 60 Hz from your mains socket as source.

If you connect two 74×57 devices, you can get a frequency division of 3600 to 1, 1800 to 1, 900 to 1, etc.

How To Use This Chip

The 74LS57 comes in a 8-pin package, and you need to connect it to 5V to power it on.

The maximum current you can pull out of one output pin is 1 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 it to generate one second timing pulses from 60 Hz.

74×57 Pinout

The 74×57 has 8 pins. It has two clock inputs, one reset input, and three divider outputs. The pins are laid out as shown in the pinout diagram below:

Pin Name	Pin #	Type	Description
CLKB	1	Input	Clock Input to the frequency divider B.
VCC	2	Power	Positive power supply (VCC). Connect to +5V power.
QA	3	Output	Output from the frequency divider A.
GND	4	Power	Connect to ground (GND).
CLKA	5	Input	Clock Input to the frequency divider A.
RST	6	Input	Reset signal that resets all the frequency dividers.
QB	7	Output	Output from the frequency divider B.
QC	8	Output	Output from the frequency divider C.

Alternatives and Equivalents for 74LS57

There are many versions of the 74×57 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:

• 74HC57 (High-speed CMOS)
• 74HCT57 (High-speed CMOS, TTL compatible)
• 74LS57 (High-speed TTL)
• 74LVC57 (Low Voltage TTL)
• 74AC57 (Advanced CMOS)
• 74ALS57 (Advanced Low-Power Schottky TTL)
• 74F57 (Very High Speed)
• 74C57 (CMOS, similar to the 4000-series)

Some manufacturers also add a prefix, such as the SN74LS57 by Texas Instruments.

Can’t find the 74×57 anywhere? Then try one of the following IC alternatives:

• 74×56 – Can generate one second timing pulses from 50 Hz (Standard European frequency).

If you can’t find the 74×57 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 74LS57 and 74HC57 chips

Download the PDF datasheet for your version of the 74×57 here:

• SN74LS57 (Texas Instruments)