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Understanding the 74LS47 BCD to 7-Segment Decoder

Understanding the 74LS47 BCD to 7-Segment Decoder

Introduction to the 74LS47

The 74LS47 is a BCD (Binary Coded Decimal) to 7-segment decoder IC. It takes a 4-bit BCD code as input and decodes it to drive a 7-segment display. The 74LS47 is manufactured by various companies like Texas Instruments, NXP, ON Semiconductor etc. It comes in a 16-pin DIP package.

Pin Configuration and Description

The pin configuration of 74LS47 is shown below:

1-7Segment Select lines a-g
8-11BCD Input lines
12Lamp Test input
13Ripple Blanking input
15Supply Voltage
16Overflow output

The BCD inputs represent the number to be displayed and the segment outputs connect to the 7-segment LED display.

How the 74LS47 Works

The 74LS47 contains combinational logic that decodes the 4-bit BCD input into appropriate signals for the 7-segment display. When valid BCD is applied, the corresponding segments are enabled. For invalid codes, the overflow output goes high to indicate error.

The lamp test input, when high, overrides the BCD input and enables all segments. The ripple blanking input is used in multi-digit displays to prevent ghosting.


  • Digital clock/counter displays
  • Electronic meters
  • Numeric displays in instruments and appliances


The 74LS47 is a simple and inexpensive BCD to 7-segment decoder suitable for driving single and multi-digit LED displays. With just 4 BCD input bits, it can decode digits from 0 to 9.

Frequently Asked Questions

Q: What is the supply voltage range for 74LS47?

A: The 74LS47 can operate from 4.75V to 5.25V.

Q: How much current can the 74LS47 sink/source?

A: The output current is typically 8mA per segment.

Q: Can 74LS47 be cascaded for multi-digit display?

A: Yes, the ripple blanking input allows cascading 74LS47s for multi-digit displays.

Q: Is 74LS47 compatible with microcontrollers?

A: Yes, the 74LS47 is compatible with TTL logic so it interfaces well with microcontrollers.

Q: What are some alternatives to the 74LS47?

A: Some alternatives are 74HC4511, MM74C948, MAX7219, etc.