What is the Difference Between Common Anode and Common Cathode

Common anode and common cathode configurations refer to the way LEDs (Light Emitting Diodes) or other multi-segment displays are connected in electronic circuits.

What is the difference between common anode and common cathode? In a common anode display, all the anodes of the seven LED segments are connected together into a single pin, whereas in a common cathode display, all the cathodes of the seven LED segments are connected together.

Key Areas Covered

1. What is a Common Anode 
      – Definition, Features 
2. What is a Common Cathode
      – Definition, Features
3. Similarities Between Common Anode and Common Cathode
      – Outline of Common Features
4. Difference Between Common Anode and Common Cathode
      – Comparison of Key Differences
5. FAQ: Common Anode and Common Cathode
      – Frequently Asked Questions

Key Terms

Common Anode, Common Cathode, LED

What is a Common Anode

Common anode refers to a specific configuration in LED displays, particularly seven-segment displays used to show numbers and some letters. In a common anode display, all the positive terminals (anodes) of the individual LED segments are linked together into a single connection point. This common anode pin is typically tied to a positive voltage source. One main advantage of common anode displays is their compatibility with many digital logic circuits. These circuits are typically better at sinking current (connecting to the ground) than sourcing current (providing positive voltage). By grounding the cathodes to turn on segments, common anode displays leverage this strength.

Common anode configurations are primarily used in seven-segment LED displays. These kinds of displays are useful in digital clocks, calculators, meters and gauges, and simple alphanumeric displays.

Beyond these common uses, common anode displays can be found in various other applications where displaying basic numbers or a limited set of alphanumeric characters is necessary. This could include simple timers and counters, control panels for appliances or industrial equipment, and DIY electronics projects where cost-effective and straightforward display solutions are needed.

What is a Common Cathode

In a common cathode setup, all the negative terminals (cathodes) of LEDs are linked and share a single connection point, typically grounded. To light up specific LEDs, we control their positive terminals (anodes). Each LED has its own anode connection. By applying a high voltage to a particular anode, current flows through that LED, making it light up.

The primary use of common cathode is in LED displays, particularly larger ones. The other uses of the common cathode are in matrix displays, and custom LED lighting projects. The common cathode has become a popular choice because of its energy efficiency and larger display.

In a common cathode configuration, all the LED cathodes are connected. This allows for more efficient power usage, especially for displays with many LEDs. The current only needs to flow through one LED at a time to light it up. This translates to lower power consumption and less heat generation.

Common cathode becomes more advantageous as the number of LEDs in a display increases. The single connection for all cathodes simplifies wiring compared to a common anode setup where each LED would need a separate ground connection.

Similarities Between Common Anode and Common Cathode

1. Both rely on the fundamental principle of LED operation.
2. Moreover, both configurations are suitable for digital control using microcontrollers or logic circuits.

Difference Between Common Anode and Common Cathode

Definition

• Common anode refers to a specific configuration in LED displays, particularly seven-segment displays used to show numbers and some letters. On the other hand, common cathode refers to a specific configuration in LED displays where individual LEDs are linked via their positive ends and driven by negative ends.

Terminals

• In a common anode, all the positive terminals (anodes) of the LEDs are connected together, while in a common cathode, all the negative terminals (cathodes) of the LEDs are connected together.

Voltage Source

• Common anode requires a single, positive voltage source connected to the common anode terminal. Meanwhile, common cathode requires a single, negative voltage source (usually ground) connected to the common cathode terminal.

Circuitry

• Common anodes generally require simpler control circuitry, while common cathodes might require slightly more complex control circuitry.

Power Efficiency

• Common anodes can be less power-efficient for large displays. Common cathodes are generally more power-efficient for large displays.

Conclusion

Common anode displays have all positive terminals connected, making them compatible with digital logic circuits that are adept at sinking current. Common cathode displays, with all negative terminals connected, offer enhanced energy efficiency and are advantageous for larger displays due to simpler wiring and lower power consumption.

FAQ: Common Anode and Common Cathode

1. Why common cathode is better than common anode?

Common cathode LED displays generally consume less power than common anode displays. This improved efficiency makes them more preferable in applications where energy conservation is important.

2. Is the common anode positive or negative?

The common anode is usually positive. This means that the anodes of the LEDs are connected to the positive terminal. Conversely, common cathode is usually negative, with the cathodes connected to the negative terminal.

3. What is the logic of the common anode?

In a common anode display, the anodes of all the LED segments are connected to a logic “1” (positive voltage). Each segment is turned on by connecting its cathode to a logic “0” (ground).

4. What are the advantages of a common cathode?

Common cathode configurations have several advantages. By connecting the cathodes of the LED segments to a common ground, these displays consume less power compared to common anode configurations. This makes them ideal for battery-powered devices and applications where energy conservation is important. Additionally, the straightforward grounding simplifies circuit design and can lead to more stable and reliable performance.

Reference:

1. “Common Anode/Cathode 7-segment displays.” The University of Hawai.

Image Courtesy:

1. “7 Segment multiplexing” By Laserlicht (CC BY-SA 4.0) via Commons Wikimedia