74LS47 BCD to 7-segment, active-low, open collector
The 74LS47 is a BCD to 7-segment decoder and driver. It takes a 4-bit binary-coded decimal digit on D C B A and drives the seven segments a to g of a display. Its outputs are active-low and open-collector, so it drives a common-anode display: a segment lights when its output goes low.
74LS47 pinout
Top view of the 16-pin DIP package. Pin 1 is at the bottom left, beside the notch, and the numbers run anticlockwise. Power is on pin 16 (VCC, +5 V) and pin 8 (GND).
| Pin | Name | Type | What it is |
|---|---|---|---|
| 1 | B | Input | Input |
| 2 | C | Input | Input |
| 3 | LT′ | Input | Input, active-low |
| 4 | BI′/RBO′ | Input | Input, active-low |
| 5 | RBI′ | Input | Input, active-low |
| 6 | D | Input | Input |
| 7 | A | Input | Input |
| 8 | GND | Ground | 0 V |
| 9 | e | Output | Open collector output |
| 10 | d | Output | Open collector output |
| 11 | c | Output | Open collector output |
| 12 | b | Output | Open collector output |
| 13 | a | Output | Open collector output |
| 14 | g | Output | Open collector output |
| 15 | f | Output | Open collector output |
| 16 | VCC | Power | +5 V supply |
74LS47 truth table
| D | C | B | A | a | b | c | d | e | f | g |
|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 1 |
| 0 | 0 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 |
| 0 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 0 |
| 0 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 0 | 0 |
| 0 | 1 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | 0 | 0 |
| 0 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 0 |
| 0 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 1 | 1 |
| 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 1 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0 |
What the 74LS47 is used for
- Showing a counter or a BCD digit on a common-anode 7-segment display
- Multi-digit displays with leading-zero blanking, using RBI′ and RBO′
For a common-anode display: anode to +5 V, each segment through its own resistor into a pin, which sinks up to 24 mA. 6 and 9 come out without their tails, and 10–15 give the datasheet’s odd symbols.
Electrical summary
| Package | 16-pin DIP |
| Supply voltage | 5 V (4.75 V to 5.25 V) |
| Supply current, typical | 7 mA |
| Output type | Open collector — only pulls low; needs a pull-up resistor or a load to the supply |
| Output current, low | sinks up to 24 mA |
| Output current, high | none — the output does not drive high |
| Input current, low | 0.4 mA out of each input held low |
| Fan-out | one output can drive about 60 LS inputs |
Typical figures for quick reference when planning a board. Check the manufacturer's datasheet for limits and timing before committing a design.
Try the 74LS47 on a breadboard
The Breadboard Simulator has the 74LS47 in its parts library: seat it on a virtual breadboard, wire it, power the board and probe the pins before you build the real thing.