SN74LS47N Pinout, Truth Table, Circuit and 7-Segment Display Guide

The SN74LS47N is a BCD-to-seven-segment decoder/driver designed to convert a 4-bit binary-coded decimal input into the seven control signals required by a numeric display.

It is particularly useful when a circuit needs to display decimal numbers from 0 to 9 without requiring a microcontroller to control every LED segment individually.

Unlike a simple logic decoder, the SN74LS47N includes several display-oriented functions, including lamp testing, display blanking, and leading- or trailing-zero suppression.

It also uses active-low, open-collector segment outputs, making it particularly suitable for common-anode seven-segment displays.

This guide explains the SN74LS47N pinout, truth table, operating principle, 7-segment wiring, control pins, Arduino interface, logic-level compatibility, component alternatives, and common troubleshooting issues.

Quick Answer: The SN74LS47N is a 16-pin BCD-to-seven-segment decoder/driver that converts four BCD inputs into seven active-low, open-collector outputs for driving a common-anode seven-segment display. Its BCD inputs are A on pin 7, B on pin 1, C on pin 2, and D on pin 6. It also provides lamp testing, display blanking, and ripple blanking for multi-digit zero suppression.

What Is the SN74LS47N?

The SN74LS47N is a member of Texas Instruments' 74LS TTL logic family. Like other semiconductor devices used in digital logic circuits , its behavior depends on defined input thresholds, supply conditions, output architecture, and load characteristics.

Its basic function is:

4-bit BCD input → seven-segment decoding → display driver outputs

A decimal digit can be represented using four binary signals:

Decimal 0 = 0000Decimal 1 = 0001Decimal 2 = 0010Decimal 3 = 0011...Decimal 9 = 1001

The SN74LS47N receives these four inputs and determines which sections of a seven-segment display should illuminate.

For example:

BCD Input0 1 0 1↓SN74LS47N↓Segments required for decimal 5

Instead of a controller having to calculate and drive seven segment signals individually, it only needs to provide the appropriate four-bit BCD value.

Key SN74LS47N Features

1. BCD-to-seven-segment decoding
2. Four BCD inputs: A, B, C, and D
3. Seven display outputs: a through g
4. Active-low segment outputs
5. Open-collector output architecture
6. Designed primarily for common-anode displays
7. Lamp-test input
8. Blanking input
9. Ripple blanking for zero suppression
10. 16-pin PDIP package for SN74LS47N

SN74LS47 vs SN74LS47N: What Does the N Mean?

The terms 74LS47, SN74LS47, and SN74LS47N are often used interchangeably online, but they do not describe exactly the same thing.

SN74LS47 refers to the device family, while SN74LS47N identifies a particular package version.

N = 16-pin PDIP package

This distinction matters when designing a PCB, repairing older equipment, or ordering a replacement component. The electrical function may be similar across package variants, but the physical package and PCB footprint are not necessarily interchangeable.

Package suffixes should also not be confused with the abbreviated markings printed on an IC body. If you are identifying an unknown or partially marked device, see our IC top marking codes guide for a practical process for checking manufacturer markings, package type, pin count, and datasheet information.

SN74LS47N Pinout

The SN74LS47N uses a 16-pin package. One of the most common mistakes when working with this IC is assuming that BCD inputs A, B, C, and D correspond sequentially to pins 1, 2, 3, and 4.

They do not.

Pin	Name	Function
1	B	BCD input, binary weight 2
2	C	BCD input, binary weight 4
3	LT	Lamp Test input
4	BI/RBO	Blanking Input / Ripple Blanking Output
5	RBI	Ripple Blanking Input
6	D	BCD input, binary weight 8
7	A	BCD input, binary weight 1
8	GND	Ground
9	e	Segment e output
10	d	Segment d output
11	c	Segment c output
12	b	Segment b output
13	a	Segment a output
14	g	Segment g output
15	f	Segment f output
16	VCC	Positive supply

SN74LS47N Pin Functions

The four BCD inputs represent different binary weights:

A = Pin 7 = Weight 1B = Pin 1 = Weight 2C = Pin 2 = Weight 4D = Pin 6 = Weight 8

The decimal value represented by these inputs can therefore be calculated as:

Decimal value = 8D + 4C + 2B + A

Understanding the A, B, C and D Inputs

For decimal 5:

D C B A0 1 0 1
= 4 + 1= 5

This input ordering is especially important when troubleshooting a circuit that displays the wrong number.

When identifying an SN74LS47N or another logic IC on an existing PCB, also verify the package orientation, pin-1 indicator, printed markings, and surrounding circuit. Our circuit board component identification guide explains how to identify ICs and other PCB components using reference designators, physical packages, markings, and circuit context.

How Does the SN74LS47N Work?

Internally, the SN74LS47N performs combinational logic decoding. The four BCD inputs represent one decimal digit, and the IC converts that value into seven segment-control outputs.

D C B A│▼┌──────────────┐│ SN74LS47N ││ BCD Decoder │└──────────────┘│a b c d e f g│▼7-Segment Display

How a Seven-Segment Display Represents Numbers

A standard seven-segment display contains seven LED sections identified as a through g:

─ a ─| |f b| |─ g ─| |e c| |─ d ─

Different combinations of these segments create different decimal digits.

For decimal 1, segments b and c are illuminated.

For decimal 7, segments a, b, and c are illuminated.

For decimal 8, all seven segments are illuminated.

The SN74LS47N automatically generates the required segment pattern from the four BCD input signals.

Active-Low and Open-Collector Outputs Explained

The segment outputs of the SN74LS47 are active low and open collector.

This means the output logic may appear reversed compared with ordinary push-pull digital outputs.

SN74LS47 segment output:
LOW = Segment ONInactive/open-collector state = Segment OFF

Rather than sourcing current into the LED segment, the SN74LS47 primarily provides a path for current to flow toward ground.

SN74LS47N Truth Table

For normal decimal operation, BCD values range from 0000 through 1001.

Decimal	D	C	B	A	Display
0	0	0	0	0	0
1	0	0	0	1	1
2	0	0	1	0	2
3	0	0	1	1	3
4	0	1	0	0	4
5	0	1	0	1	5
6	0	1	1	0	6
7	0	1	1	1	7
8	1	0	0	0	8
9	1	0	0	1	9

What Happens With BCD Inputs 10–15?

Four input bits can represent sixteen binary combinations, but BCD uses only ten of them for decimal digits.

Valid decimal BCD:0000 through 1001
Outside normal decimal BCD:1010 through 1111

Values from 1010 through 1111 therefore do not represent valid decimal digits 0 through 9.

The SN74LS47 may generate recognizable non-decimal segment patterns for these input combinations rather than simply displaying a normal digit. This can be useful when debugging counters or digital-logic circuits that accidentally produce invalid BCD values.

Why Does the SN74LS47 Use a Common-Anode Display?

Because the SN74LS47 uses active-low, open-collector segment outputs, it is normally paired with a common-anode seven-segment display.

In a common-anode display, the positive side of the LED segments shares a common connection.

+5 V│Common Anode│LED Segment│Current-Limiting Resistor│SN74LS47 Output│GND

When the relevant SN74LS47 output is pulled low, current can flow through the LED segment and the segment illuminates.

This current-sinking behavior is one of the most important concepts to understand when designing or troubleshooting a 74LS47 display circuit.

SN74LS47N Circuit With a 7-Segment Display

A basic SN74LS47N circuit consists of a BCD signal source, the decoder/driver, seven current-limiting resistor paths, and a common-anode seven-segment display.

BCD Source│▼SN74LS47N│a b c d e f g│Current-Limiting Resistors│Common-Anode7-Segment Display

SN74LS47N Pin	Connect To
Pin 16 — VCC	Positive supply
Pin 8 — GND	Ground
Pin 7 — A	BCD bit 0
Pin 1 — B	BCD bit 1
Pin 2 — C	BCD bit 2
Pin 6 — D	BCD bit 3
Pin 13 — a	Display segment a
Pin 12 — b	Display segment b
Pin 11 — c	Display segment c
Pin 10 — d	Display segment d
Pin 9 — e	Display segment e
Pin 15 — f	Display segment f
Pin 14 — g	Display segment g

Do You Need Resistors With a 74LS47?

Yes.

A current-limiting resistor should normally be placed in series with each LED segment.

Without appropriate current limiting, excessive current can damage the LED display or operate the driver outside its intended electrical conditions.

The correct resistance depends on:

1. Supply voltage
2. LED forward voltage
3. Desired LED current
4. Display construction
5. SN74LS47 output voltage at the selected current

How to Calculate the Segment Resistor

A simplified resistor calculation is:

R = (VSUPPLY - VF - VOL) / ILED

For example:

VSUPPLY = 5 VVF = 2 VVOL ≈ 0.3 VILED = 8 mA

Then:

R ≈ (5 - 2 - 0.3) / 0.008R ≈ 337.5 Ω

A nearby standard resistor value can then be selected after checking the electrical limits of the specific display and driver.

Do not assume that 220 Ω or 330 Ω is automatically correct for every seven-segment display.

What Do LT, RBI and BI/RBO Do?

The SN74LS47 contains three display-control functions that often confuse first-time users:

1. LT
2. RBI
3. BI/RBO

These pins are not part of the four-bit BCD value. They control testing, blanking, and zero suppression.

LT: Lamp Test

LT stands for Lamp Test.

Its purpose is to illuminate the display segments so the display and segment connections can be checked independently of normal BCD decoding.

Lamp Test asserted↓Segments illuminate↓Check display operation

If one segment fails to illuminate during a correct lamp test, possible causes include:

1. A failed LED segment
2. An open current-limiting resistor
3. Incorrect segment wiring
4. A damaged PCB trace
5. A driver output fault

RBI: Ripple Blanking Input

RBI means Ripple Blanking Input.

It is primarily used in multi-digit displays to suppress unnecessary leading or trailing zeros.

For example:

Without leading-zero suppression:0025
With leading-zero suppression:25

Ripple blanking allows several decoder stages to coordinate this behavior.

BI/RBO: Blanking Input / Ripple Blanking Output

Pin 4 performs two related functions:

1. BI — Blanking Input
2. RBO — Ripple Blanking Output

The blanking function can turn the display off regardless of the normal BCD value.

The ripple-blanking output allows blanking information to propagate between multiple decoder stages, making automatic zero suppression possible in multi-digit displays.

How to Connect the SN74LS47N Step by Step

The following workflow can be used for a basic one-digit display circuit.

Step 1: Connect the Power Supply

Pin 16 → VCCPin 8 → GND

Use the supply conditions specified for the SN74LS47 and the surrounding 74LS logic system.

Step 2: Connect the BCD Inputs

Pin 7 → APin 1 → BPin 2 → CPin 6 → D

Remember:

A = LSBD = MSB

Step 3: Connect the Segment Outputs

Pin 13 → aPin 12 → bPin 11 → cPin 10 → dPin 9 → ePin 15 → fPin 14 → g

Each segment connection should include appropriate current limiting.

Step 4: Connect the Common-Anode Display

Use a common-anode seven-segment display and connect its common-anode terminal or terminals according to the display manufacturer's specifications.

Do not assume that all seven-segment displays use the same physical package pinout. Always verify the selected display's datasheet.

Step 5: Configure LT, RBI and BI/RBO

LT, RBI, and BI/RBO must be placed in appropriate logic states for ordinary display operation.

Do not intentionally leave display-control inputs undefined in a finished design.

Unexpected states can cause:

1. All segments to illuminate
2. The display to remain blank
3. Unexpected zero suppression

SN74LS47N With Arduino

The SN74LS47 can also be controlled by a microcontroller such as an Arduino.

Instead of using seven microcontroller GPIO pins to control seven individual LED segments, four GPIO outputs can provide the BCD input value.

Arduino Wiring

Arduino D2 → SN74LS47 AArduino D3 → SN74LS47 BArduino D4 → SN74LS47 CArduino D5 → SN74LS47 D

The SN74LS47 then converts the four-bit value into the correct seven-segment pattern.

Arduino Example Code

const int pinA = 2;const int pinB = 3;const int pinC = 4;const int pinD = 5;
void setup() {pinMode(pinA, OUTPUT);pinMode(pinB, OUTPUT);pinMode(pinC, OUTPUT);pinMode(pinD, OUTPUT);}
void displayDigit(byte digit) {digitalWrite(pinA, bitRead(digit, 0));digitalWrite(pinB, bitRead(digit, 1));digitalWrite(pinC, bitRead(digit, 2));digitalWrite(pinD, bitRead(digit, 3));}
void loop() {for (byte digit = 0; digit <= 9; digit++) {displayDigit(digit);delay(1000);}}

The bit mapping is:

A ← bit 0B ← bit 1C ← bit 2D ← bit 3

For example:

Decimal 5 = Binary 0101

The decoder receives 0101 and generates the required segment pattern for the digit 5.

Can a 3.3V Microcontroller Drive the SN74LS47?

This question requires more analysis than simply saying that the SN74LS47 is a 5V logic device and therefore always requires a level shifter.

Logic compatibility depends on input and output voltage thresholds rather than nominal supply voltage alone.

For the SN74LS47 logic inputs, an important comparison is:

VIH minimum = 2.0 VVIL maximum = 0.8 V

A 3.3V CMOS output can therefore often produce a HIGH voltage that exceeds the SN74LS47's required HIGH threshold.

However, designers should still verify:

1. The MCU's guaranteed VOH at the relevant load current
2. The MCU's guaranteed VOL
3. SN74LS47 input current
4. Shared ground
5. Power sequencing
6. Protection requirements
7. Whether any 5V signal can feed back into the 3.3V device

A 3.3V logic HIGH may satisfy the SN74LS47 input threshold, but interface compatibility should be verified using the guaranteed specifications of the actual microcontroller rather than nominal voltage alone.

SN74LS47 vs SN74LS48

The SN74LS47 and SN74LS48 perform closely related BCD-to-seven-segment functions, but their display-driving arrangements differ.

Feature	SN74LS47	SN74LS48
Function	BCD-to-7-segment decoder/driver	BCD-to-7-segment decoder/driver
Segment logic	Active LOW	Active HIGH
Output style	Open collector	Different output arrangement suited to its target display type
Typical display	Common anode	Common cathode
Lamp test	Yes	Yes
Ripple blanking	Yes	Yes

The two devices should therefore not be treated as direct substitutes without checking the display type, output behavior, pinout, and electrical requirements.

Practical Selection Rule

For a conventional common-anode seven-segment display, the 74LS47 is the more typical choice.

For a common-cathode display, a decoder/driver designed for active-high segment control, such as the 74LS48 family, may be more appropriate.

7447 vs 74LS47: What Is the Difference?

The classic 7447 and 74LS47 perform the same general BCD-to-seven-segment function, but they belong to different TTL logic generations.

The LS in 74LS47 means:

Low-Power Schottky

The 74LS family was developed to provide improved power/performance characteristics compared with earlier standard TTL families.

In replacement work, however, do not decide compatibility solely from the base function or a similar part number. Two devices may perform the same logic function while differing in package, output characteristics, electrical limits, timing, temperature rating, or other implementation details.

Before substituting one logic IC for another, follow a structured pin-to-pin replacement compatibility check rather than assuming that functionally similar parts are automatically drop-in compatible.

When evaluating another manufacturer or a newer device family, it is also important to distinguish between a functional equivalent, a pin-compatible alternative, and a true drop-in replacement. See our cross-reference vs drop-in compatibility guide before approving an alternate component for production or repair.

Common SN74LS47N Applications

Although the SN74LS47 is associated with classic TTL logic systems, it can still be useful in:

1. Digital counters
2. Laboratory instruments
3. Digital-logic education
4. Frequency counters
5. Event counters
6. Scoreboards
7. Basic numeric displays
8. Legacy equipment repair
9. Industrial panel displays
10. Test fixtures
11. 74-series logic demonstrations

A typical signal chain is:

Clock / Sensor Pulses↓BCD Counter↓SN74LS47↓7-Segment Display

The BCD counter generates the four-bit decimal count, while the SN74LS47 performs the segment decoding.

Multiple-Digit Displays and Zero Suppression

One useful feature of the SN74LS47 is its support for ripple blanking.

Consider a three-digit display representing the number 5:

Without suppression:005
With leading-zero suppression:5

By linking ripple-blanking signals across multiple decoder stages, unnecessary leading zeros can be removed automatically.

This was especially useful in counters, measurement instruments, and other digital systems built from discrete logic rather than microcontrollers.

SN74LS47N Troubleshooting Guide

Display Stays Completely Dark

Check:

1. Pin 16 is connected to the correct supply
2. Pin 8 is connected to ground
3. The display is common anode
4. The display common terminal is connected correctly
5. BI/RBO is not forcing blanking
6. The current-limiting resistors are intact
7. The segment wiring matches the display pinout

All Segments Stay Illuminated

Check the LT input first. Lamp Test can override normal BCD decoding and illuminate all display segments.

Also verify that the control input is not unintentionally being held in its asserted state.

Wrong Number Appears

Check the BCD input wiring carefully.

A = Pin 7B = Pin 1C = Pin 2D = Pin 6

A wiring mistake here can make the decoder appear faulty even when the IC is operating normally.

Individual Segments Are Incorrect

Check the segment output mapping:

a = Pin 13b = Pin 12c = Pin 11d = Pin 10e = Pin 9f = Pin 15g = Pin 14

Also verify the physical pinout of the seven-segment display itself.

Strange Characters Appear Above 9

Inputs from 1010 through 1111 are outside normal decimal BCD operation.

Normal decimal range:0000–1001

If a counter or microcontroller supplies values above decimal 9, the display may show non-decimal segment patterns.

Leading Zeros Will Not Disappear

Inspect:

1. RBI
2. BI/RBO
3. The connections between decoder stages

Zero suppression depends on the correct ripple-blanking configuration.

Display Brightness Is Too Low

Check:

1. Segment resistor values
2. LED forward voltage
3. Driver current
4. Supply voltage
5. Wiring resistance
6. The total load placed on the driver

Do not reduce resistor values blindly. Confirm the display current and driver limits first.

Common Mistakes When Using a 74LS47

1. Using a common-cathode display: The SN74LS47 is intended primarily for common-anode display driving.
2. Assuming pins 1–4 are A–D: The BCD inputs are A = pin 7, B = pin 1, C = pin 2, and D = pin 6.
3. Omitting segment resistors: Each LED segment needs suitable current limiting.
4. Ignoring LT, RBI, or BI/RBO: Incorrect states on these pins can override ordinary decoding.
5. Treating the outputs like ordinary GPIO: SN74LS47 segment outputs are active-low and open collector.
6. Sending values above decimal 9: BCD values 1010 through 1111 are outside the normal decimal range.

SN74LS47N Key Specifications

Parameter	SN74LS47N
Device type	BCD-to-seven-segment decoder/driver
Logic family	LS TTL
BCD inputs	4
Segment outputs	7
Segment output logic	Active LOW
Output configuration	Open collector
Typical display type	Common anode
Lamp test	Yes
Ripple blanking	Yes
SN74LS47N package	16-pin PDIP

Is the SN74LS47N Still Useful?

For a completely new product, a microcontroller, integrated LED driver, or multiplexed display controller may provide more flexibility.

However, the SN74LS47 remains relevant in several situations.

1. Maintaining legacy TTL equipment
2. Repairing existing 74LS47-based circuits
3. Teaching combinational logic
4. Building simple counters
5. Interfacing BCD counters with numeric displays
6. Replacing failed devices without redesigning the complete display system

For legacy equipment, keeping the original SN74LS47 architecture may be simpler and lower risk than redesigning the entire display circuit.

If an exact device becomes difficult to source, proposed alternatives should be checked for electrical, mechanical, thermal, and functional compatibility before substitution.

You can also view the SN74LS47N product page for component information or submit the part number to Octatronics for availability and sourcing support.

Frequently Asked Questions

What Is the SN74LS47N?

The SN74LS47N is a BCD-to-seven-segment decoder/driver from the 74LS TTL logic family. It accepts a four-bit BCD value and generates seven segment-control outputs for a numeric display.

What Type of Seven-Segment Display Works With a 74LS47?

The 74LS47 is intended primarily for common-anode seven-segment displays because its outputs are active low and open collector.

What Is the SN74LS47N Pinout?

The four BCD input pins are:

A = Pin 7B = Pin 1C = Pin 2D = Pin 6

VCC is pin 16, GND is pin 8, and the seven segment outputs are on pins 9 through 15.

What Does LT Mean on the 74LS47?

LT means Lamp Test. It is used to illuminate the display segments for testing independently of the normal BCD input value.

What Does RBI Mean on the 74LS47?

RBI means Ripple Blanking Input. It is part of the zero-suppression system used in multi-digit displays.

What Is BI/RBO on the 74LS47?

BI/RBO means Blanking Input / Ripple Blanking Output. It can blank the display and propagate blanking information between decoder stages.

Is the 74LS47 Output Active High or Active Low?

The seven segment outputs are active low. Pulling the relevant output low allows the corresponding segment to illuminate in the intended common-anode circuit.

Can the SN74LS47 Drive a Common-Cathode Display?

A common-cathode display is not the normal configuration for the SN74LS47. The SN74LS47 is designed primarily around active-low driving of common-anode displays.

Does the SN74LS47 Need Current-Limiting Resistors?

Yes. Each LED segment requires appropriate current limiting. The correct resistor value depends on supply voltage, LED forward voltage, desired current, and driver characteristics.

Can an Arduino Control a 74LS47?

Yes. Four Arduino digital outputs can provide the BCD inputs A through D, allowing the SN74LS47 to generate the seven segment-control signals.

Can 3.3V Logic Drive the SN74LS47?

A 3.3V logic output can often satisfy the SN74LS47 input-high threshold, but compatibility should be confirmed using the guaranteed VOH and VOL specifications of the specific microcontroller.

What Happens When the SN74LS47 Input Is Greater Than 9?

BCD values 1010 through 1111 are outside the normal decimal range. The decoder may therefore generate non-decimal segment patterns rather than digits 0 through 9.

Conclusion

The SN74LS47N is more than a basic BCD decoder. It combines BCD-to-seven-segment conversion with active-low open-collector outputs, lamp testing, display blanking, and ripple blanking for multi-digit zero suppression.

The most important points to remember are:

1. It accepts four BCD inputs.
2. A is pin 7, not pin 1.
3. The seven segment outputs are active low.
4. The outputs use an open-collector architecture.
5. It is intended primarily for common-anode seven-segment displays.
6. Each LED segment requires appropriate current limiting.
7. LT provides lamp testing.
8. RBI and BI/RBO support display blanking and zero suppression.
9. BCD inputs above decimal 9 are outside normal decimal operation.
10. SN74LS47N identifies the 16-pin PDIP package version.

For legacy-equipment repair, digital-logic education, counter circuits, and straightforward BCD display systems, the SN74LS47N remains a useful device to understand.

Need an SN74LS47N or a compatible logic IC?

Octatronics helps engineers source electronic components and evaluate alternatives for prototypes, maintenance, and production requirements.

View SN74LS47N | Request a Quote