IC 74247 – BCD to 7-Segment Decoder/Driver

IC 74247 – BCD to 7-Segment Decoder/Driver with Open-Collector Outputs

Overview

The IC 74247 is a Binary Coded Decimal (BCD) to 7-segment decoder/driver designed for driving common-anode displays. It converts a 4-bit BCD input into signals that will illuminate the appropriate segments of a 7-segment display to represent numbers 0 through 9. The IC features open-collector outputs, making it suitable for interfacing with various types of displays and allowing for external pull-up resistors to be used.

Features

• BCD to 7-Segment Conversion: Converts 4-bit BCD input to the corresponding 7-segment code.
• Open-Collector Outputs: Allows for interfacing with higher voltage levels or using wired-AND logic.
• Supports Common-Anode Displays: Specifically designed to drive common-anode 7-segment displays.
• Standard TTL Compatibility: Compatible with standard TTL logic levels.
• Lamp Test and Blanking Inputs: Provides functionality for testing and controlling display visibility.

Pin Configuration

The IC 74247 is typically housed in a 16-pin Dual In-line Package (DIP) with the following pin configuration:

• Pins 1, 2, 6, 7: BCD Inputs (D, C, B, A) for the binary-coded decimal input.
• Pin 3: Lamp Test (LT) input to illuminate all segments for testing purposes.
• Pin 4: Blanking (BI) input to disable all outputs (turn off the display).
• Pins 9-15: Outputs (a, b, c, d, e, f, g) to drive the corresponding segments of the 7-segment display.
• Pin 8: Ground (GND).
• Pin 16: Positive Supply Voltage (Vcc).

Working Principle

1. BCD Input: The IC receives a 4-bit BCD input representing numbers from 0 to 9.
   • Example: BCD input of “0101” corresponds to the number 5.
2. 7-Segment Output: The IC decodes the BCD input and generates the appropriate signals to drive the 7-segment display.
   • Example: For the number 5, the segments a, c, d, f, and g would be illuminated.
3. Open-Collector Outputs: The IC’s outputs are open-collector, meaning they can only sink current. External pull-up resistors are required to pull the output lines to a high state when not active.
4. Control Inputs:
   • Lamp Test (LT): When active, all segments of the display are turned on, allowing for a quick test of the display.
   • Blanking Input (BI): When active, all outputs are disabled, effectively turning off the display.

Applications

• Digital Clocks: Used in digital clocks to display time.
• Counters and Timers: Converts BCD output from counters and timers to a 7-segment display format.
• Scoreboards: Drives 7-segment displays in electronic scoreboards.
• Calculators: Displays numeric output in basic calculators.

Example Circuit

• Digital Clock Display: In a digital clock circuit, the IC 74247 could be used to decode the BCD output from a timekeeping chip and drive a 7-segment display to show the hours and minutes.

Advantages

• Efficient BCD to 7-Segment Conversion: Simplifies the design of circuits requiring numeric displays.
• Flexible Output Configuration: Open-collector outputs allow for interfacing with different logic levels.
• Integrated Lamp Test and Blanking: Provides additional control over the display.

Conclusion

The IC 74247 is a versatile BCD to 7-segment decoder/driver, particularly useful in applications where a common-anode 7-segment display needs to be driven. Its ability to convert BCD inputs into readable numeric displays, coupled with the flexibility of open-collector outputs, makes it a critical component in a wide range of digital electronics projects. Whether you are building clocks, timers, or any system requiring numeric output, the IC 74247 provides a reliable and straightforward solution for 7-segment display driving.

IC 7440 – Dual 4-Input NAND Gate with Open-Collector Outputs