Common Cathode vs Common Anode: Comparing LED Display Configurations

Common cathode and common anode are two compact and efficient LED pin configurations that offer distinct benefits. In this article, you will learn the difference between the two, their advantages, and their weaknesses.

What is Common Cathode?

Common cathode is a design method in LED displays, where the cathodes of each LED are connected together to a common ground or a negative voltage. The anodes of each LED, subsequently, are connected to individual control lines. In order to light an LED, voltage is applied at the control line of the anode, reducing the forward voltage drop and causing the current to flow from the anode towards the common cathode.

Since the control terminals in common cathode configuration are anodes, this circuit works using the active high logic. Each LED is turned on by applying a high voltage at its anode. This makes it ideal for RGB displays and microcontroller interfacing.

What is a Common Anode?

Common anode is another pin configuration in LED displays, where the anodes of each LED are connected together to a common positive voltage. The cathodes of each LED, subsequently, are connected to an individual control line. When a negative voltage is applied on one of these control lines, the forward voltage drop increases and current starts to flow from the anode to the cathode, thus lighting the LED.

Since the control terminals in the common anode configuration are cathodes, this circuit works using the active low logic. Each LED is turned on by applying a low voltage at the cathode. This makes it ideal for seven-segment displays and high-side switching applications.

Common Cathode vs Common Anode: Which is the Better LED Configuration?

While both common anode and common cathode are design methods for operating LED displays, they are sufficiently different to provide unique benefits in different cases. In order to understand which is the best configuration for your application, it is necessary to understand the differences between common cathode and common anode in detail.

Connections

In common cathode pin configuration, the cathodes of each LED are connected together to a common ground or negative voltage. The anodes of the LED are individual control lines supplied with positive voltage from a source.

On the other hand, in a common anode pin configuration, the anodes of each LED are connected together to a common positive voltage. The cathodes of each LED, in turn, are connected to individual control lines supplied with negative voltage.

Current Flow

Current flows in common cathode configuration when a positive voltage is applied at the anode of the LED. The direction of current flow is from high voltage to low voltage, therefore, it travels through a resistor into the anode of the LED, illuminating it. It then travels towards the common cathode and finally into the common ground or negative terminal.

In contrast, when a negative voltage is applied to the control line of the cathode in a common anode configuration, current begins to flow from the common positive voltage. It travels through a resistor into the anode of the LED, lighting it, and continues into the control line of the cathode, finally terminating at a grounded element.

 Supply Voltage

In common cathode configuration, each individual LED is supplied with positive voltage through the control line when it is required to be turned on. The value of voltage supplied is 5V or 3.3V for seven-segment LED displays. In RGB LED displays, however, each color requires a different voltage value: red operates at 1.8V, while green and blue typically require 2.8V. Since voltage is applied independently, each LED can be powered separately, thus reducing the power consumption.

The value of supply voltage is similar for common anode configuration in case of a seven segment display. The common positive voltage applied is 5V to 3.3V. In RGB displays, however, since the voltage applied is through a common channel, individual LEDs are powered through a single voltage of 5V, which increases the power consumption of the circuit.

Energy Efficiency

Power consumption in common cathode configuration can be managed efficiently due to individual voltage supply to each anode. This allows a circuit designer to supply controlled levels of voltage to each LED.

As the voltage applied to the LED array is the same value in common anode configuration, it can lead to excess power consumption in some applications like RGB displays. In such cases, the circuit may require additional devices such as transistors or MOSFETs to increase energy efficiency.

Applications

Common cathode configuration is easier to integrate into circuits which operate upon active high logic, since the LEDs are activated from the anode and require a positive voltage. Common anode configuration is suitable for circuits which operate upon a positive logic system, due to its common high voltage. However, their integration is sometimes complicated due to their use of active low at the cathode side.

Common Cathode

1. RGB Displays: Common cathode configuration is often used in RGB displays due to energy efficiency and simplicity of operation.
2. LED Matrices: In dot matrix displays, the common cathode provides simple control of the LEDs by grounding the cathode.
3. Microcontroller Projects: Common cathode configuration provides ideal interfacing with microcontrollers by direct control through GPIO pins.

Common Anode

1. Seven Segment Displays: Provides simple integration into circuits with positive logic systems.
2. High-Side Switching Circuits: In high side switching circuits where positive voltage is common and grounding is required for operating LED, common anode is the preferred LED configuration.
3. Display Modules: Several modules use a common high voltage to operate, which makes this configuration ideal for them.

Conclusion

Both common cathode and common anode are important configurations for LED displays with their own unique benefits. While common cathode provides more energy efficiency in several use cases, common anode is simple to integrate with most circuits. The choice of configuration ultimately depends upon your application, circuit design, power supply design and control logic.