Quick answer
There are only three ways to wire an LED display: direct connection, common anode, and common cathode. The last two are easy to mix up on paper and expensive to mix up on a board. Common anode wiring joins the positive sides of multiple LEDs together. These different connection types are necessary for various product applications.
When you use LEDs in a product, the most common wiring methods are common anode and common cathode. However, there is a third, less-known method. This article will explain all three common connection types and why these different methods are necessary. We’ll also provide examples for each.
Table of Contents
The Three most common LED connection methods
There are about four main ways to connect LEDs in products, and here are the three most common ones:
- Direct configuration
- Common anode configuration
- Common Cathode configuration
| Common Anode | Common Cathode | |
|---|---|---|
| Shared pin connects to | Positive supply (V+) | Ground (GND) |
| To light a segment | Pull the segment pin LOW | Drive the segment pin HIGH |
| Driver type it pairs with | Current-sinking driver | Current-sourcing driver |
| How to identify | See the part-number section below | See the part-number section below |
| Mixing them up | Display stays dark or ghosting — not damage in most driver setups, but the board needs rework | Same |
Direct configuration
The Direct Configuration is the most basic way to light up an LED. For an LED to turn on, you just need to meet four simple conditions:
- A higher voltage connects to the LED’s positive (+) side.
- A lower voltage connects to the LED’s negative (-) side.
- The voltage difference is slightly higher than the LED’s forward voltage (if the voltage is too high, the LED will burn out).
- The current flowing through the LED is less than its maximum limit (if the current is too high, the LED will burn out).
This method is simple: you control the voltage difference so that it is slightly above the LED’s forward voltage. An LED driven from a constant-voltage supply must always have its current limited. Its I–V curve rises steeply, so a small change in voltage produces a large change in current and destroys the die. In practice a series resistor is used: R = (V_supply − V_F) / I_F. For a seven-segment display this matters more than usual: the current-limiting resistor must be placed in each individual segment path (a–g and DP), not as a single resistor on the common pin. With one shared resistor, the more segments lit at once, the less current each one gets — an “8” will be visibly dimmer than a “1”. You can learn more about how to design a current-limiting resistor in this article.
Common Anode configuration
Common anode is a way to connect multiple LEDs together. It works by connecting the positive (+) side (anode) of several LEDs to a single point.
For example, look at the circuit diagram for the OPS-S4010SE-GW above. It connects the anodes of eight LEDs (labeled A-G and Dp) together. The negative (-) side (cathode) of each LED is connected to its own separate output pin.
The principle for lighting up a common anode LED is the same as the direct configuration: you just need to apply the correct voltage across the LED. If the voltage is too high, you’ll use a current-limiting resistor in the circuit to prevent the LED from burning out. The resistor and the LED can be placed in either order and will still work correctly
Common Cathode configuration
Common cathode is a way to connect multiple LEDs by joining the negative (-) side (cathode) of several LEDs to a single point.
For example, the circuit diagram for the OPS-S4011SE-GW shows the cathodes of eight LEDs (labeled A-G and Dp) connected together. The positive (+) side (anode) of each LED is connected to its own separate output pin.
Just like with the direct configuration, you light up a common cathode LED by applying the correct voltage across it. If the voltage is too high, you must use a current-limiting resistor to prevent the LED from burning out. The resistor and the LED can be placed in either order and will still work correctly.
Why Do We Have Fixed LED Connection Methods?
There are two main reasons for using fixed LED connection methods like common anode or common cathode:
- To reduce the number of wires and connections.
- To be able to light up each LED individually.
For example, a common anode seven-segment display uses fewer external pins than a direct connection method. If you used a direct connection, you would need more pins, which would waste space on the circuit board (PCB). By using a common anode or common cathode setup, you can still light up each LED individually while keeping the number of pins and the overall size of the module smaller. This is why these connection methods are used so often in LED products.
The three most common LED connection methods
| Method | How it is connected | Note |
|---|---|---|
| Direct configuration | Higher voltage to (+), lower voltage to (−), with the voltage difference slightly above the LED’s forward voltage | The most basic way to light a single LED |
| Common anode | Positive (+) sides of multiple LEDs joined to a single common point | Groups multiple LEDs |
| Common cathode | Negative (−) sides of multiple LEDs joined to a single common point | Groups multiple LEDs |
How to identify common anode or common cathode from the part number
OPTO PLUS part numbers show the polarity in one digit. In the REF-code position, an even number (0, 2, 4, 6, 8) means common anode, and an odd number (1, 3, 5, 7, 9) means common cathode. For dot matrix displays, the same rule shows the array polarity: an even number means anode column with cathode row, and an odd number means the opposite.
Here are two examples from our catalog. OPS-S5620SB is a common anode display. OPS-S5621SB is the same display in common cathode. OPD-M28810SA and OPD-M28811SA are the same 8×8 dot matrix with opposite row and column polarity.
Every standard OPTO PLUS display is available as a common anode and common cathode pair. You do not need to change your driver design to use our parts.
Which configuration should you choose?
Why do engineers still hesitate between common anode and common cathode? Because they look for the answer on the display side, while the answer is on the driver side. The two versions of the same display have identical optical and electrical performance — the same brightness, the same wavelength, the same ratings. Therefore the selection follows three steps: first, confirm whether your driver sources or sinks current; second, confirm which polarity your decoder or scan IC is designed for; finally, check the total current on the common pin. The table below covers the first two steps.
| Your driving method | Suggested type | Reason |
|---|---|---|
| Source driver or high-side switch (PNP, P-MOSFET) | Common cathode | The driver supplies current; the display common pin connects to ground |
| Sink driver or low-side switch (NPN, N-MOSFET, ULN2003) | Common anode | The driver sinks current; the display common pin connects to VCC |
| 74HC47 BCD-to-7-segment decoder (open collector) | Common anode | The 47 series is designed for common anode |
| 74HC48 or CD4511 decoder (source output) | Common cathode | The 48 and 4511 series are designed for common cathode |
| MAX7219, TM1637, and similar scan driver ICs | Check the IC datasheet | Most scan drivers are designed for one fixed polarity |
| MCU GPIO direct drive with one resistor per segment | Either type | A GPIO pin can source or sink current |
One reminder about the common pin current
Each segment carries its own current, for example 10 mA. The common pin carries the total current of all segments that are on at the same time. When the display shows “8” with the decimal point, the common pin carries 8 × 10 mA = 80 mA. Please check the maximum pin current of your driver against this total, and apply derating when you use multiplexing.
Displays Available in Both Configurations
Many OPTO PLUS LED display families are offered in both common-anode and common-cathode versions — check the part-number table on each product page:
Not sure which configuration your driver needs? Ask our engineers.
Conclusion
The Direct Configuration is great for lighting up a single LED, but when a product has many LEDs, using the Common Anode or Common Cathode methods is better. These methods reduce the number of output pins while still allowing you to light up each LED individually using the same direct-lighting principle.
Opto Plus is a Taiwan LED manufacturer operating since 2009. We produce a wide range of standard products with both common anode and common cathode connections, including:
SMD and THT 7-segment displays
SMD and THT alphanumeric displays
SMD and THT dot matrix displays
We also offer custom-made SMD and THT LED displays. If you have any needs, feel free to contact us at Sales@opledtw.com or through our contact form.
Related article
What is RGB SMD LED? | SMD LED Packaging | Full Series RGB LED Comparison Table
Dot-Matrix Displays: Names, Types, Internal Structure, and Applications
7-Segment vs. 16-Segment LED Displays: Types and Internal Structures
How 7-Segment and 16-Segment LED Displays Show Numbers and Letters
How Dot-Matrix Displays Show Digits, Letters, and Pixel Graphics
Two things to settle before the schematic is frozen
First, common anode versus common cathode is a driver-side decision, not an optical one. The two versions of the same display emit identically; what differs is which end of the LED your driver pulls. So choose whichever matches the driver IC you already have on the board, rather than treating one as technically better.
Second, on our part numbers the polarity is readable from the number itself. The reflector-cover serial number carries it: an even number is common anode, an odd number is common cathode. That is why parts arrive in pairs such as 4020 and 4021, or 5620 and 5621 — same display, opposite polarity. Checking that one digit before ordering catches most of the wiring mistakes we see.
FAQ
What are the three most common LED connection methods?
－Direct Configuration: The most basic way to light up a single LED.
－Common Anode Configuration: A method where the positive (+) side of multiple LEDs are connected together.
－Common Cathode Configuration: A method where the negative (-) side of multiple LEDs are connected together.
No matter how you connect it, to light up an LED, you must meet these four basic conditions:
－The positive (+) side of the LED needs a higher voltage.
－The negative (-) side of the LED needs a lower voltage.
－The voltage difference between the two sides must be slightly more than the LED’s forward voltage (too much voltage will burn it out).
－The current flowing through the LED must be less than its maximum limit (too much current will burn it out).
Common anode configuration is a way of connecting multiple LEDs by joining all their positive (+) sides (anodes) to a single point.
In this setup, all the LED anodes share one common connection, while the negative (-) sides (cathodes) are each wired to their own separate pin. To light up a specific LED, you just need to apply the correct voltage to its individual cathode pin.
Common cathode configuration is the opposite of common anode. In this method, the negative (-) sides (cathodes) of multiple LEDs are connected together to a single point.
All the LED cathodes share one common connection, while the positive (+) sides (anodes) are each wired to their own separate pin. To light up a specific LED, you need to apply the correct voltage to its individual anode pin.
LED products use common anode or common cathode connections mainly for two reasons:
－To control each LED: These common connections still let you turn on each individual LED separately, using the same direct-lighting method.
No. The polarity is fixed by the internal wiring of the display. Please order the odd or even part number instead. Both versions exist for standard models.
No. Both versions use the same LED count and the same package, and both are standard products.
Need a configuration, pin layout or digit arrangement we don’t stock? Our custom LED display service covers what can be changed, the sampling schedule and how MOQ is quoted case by case.