Common Anode vs. Common Cathode

Attribute	Common Anode	Common Cathode
Definition	An LED configuration where the anode (+) terminal is connected to a positive voltage source.	An LED configuration where the cathode (-) terminal is connected to a negative voltage source.
Operation	LED lights up when a positive voltage is applied to the anode terminal.	LED lights up when a negative voltage is applied to the cathode terminal.
Current Flow	Current flows from the anode to the cathode.	Current flows from the cathode to the anode.
Voltage Polarity	Positive voltage is applied to the anode terminal.	Negative voltage is applied to the cathode terminal.
Symbol
Usage	Commonly used in multiplexed displays and driver circuits.	Commonly used in digital logic circuits and driver circuits.

Introduction

When it comes to electronic circuits and displays, two common configurations are often used: common anode and common cathode. These configurations determine how the circuit is connected and how the display operates. In this article, we will explore the attributes of common anode and common cathode, highlighting their differences and applications.

Common Anode

In a common anode configuration, the anode of all the LEDs or segments in a display are connected together and connected to a positive voltage source. The cathodes of each LED or segment are then individually controlled to turn them on or off. This means that when a segment's cathode is connected to ground (0V), current flows through the LED, causing it to light up.

One of the main advantages of common anode displays is that they require fewer current-limiting resistors. Since the anode is connected to a positive voltage source, the current-limiting resistors can be placed in series with each cathode. This reduces the number of resistors needed, simplifying the circuit design and reducing costs.

Common anode displays are commonly used in applications where multiplexing is required. Multiplexing is a technique where multiple LEDs or segments are controlled using a smaller number of pins on a microcontroller or driver. By connecting the anodes together, the common anode display can be easily multiplexed, allowing for more efficient use of pins and reducing the complexity of the circuit.

However, one drawback of common anode displays is that they require a negative voltage to turn off the LEDs or segments. This can be a limitation in certain applications where a negative voltage source is not readily available.

In summary, common anode displays have the advantage of requiring fewer current-limiting resistors and are suitable for multiplexing applications. However, they require a negative voltage to turn off the LEDs or segments.

Common Cathode

In contrast to common anode displays, common cathode displays have all the cathodes of the LEDs or segments connected together and connected to ground (0V). The anodes of each LED or segment are then individually controlled to turn them on or off. When an LED's anode is connected to a positive voltage source, current flows through the LED, causing it to light up.

One of the main advantages of common cathode displays is that they can be easily interfaced with most microcontrollers and drivers. Since the cathodes are connected to ground, the microcontroller or driver can directly control the current flow by applying a positive voltage to the anodes. This simplifies the circuit design and makes it easier to control the display.

Common cathode displays are commonly used in applications where a positive voltage source is readily available, such as battery-powered devices. They are also suitable for applications where individual control of each segment is required, without the need for multiplexing.

However, one drawback of common cathode displays is that they require more current-limiting resistors compared to common anode displays. Since the cathodes are connected to ground, the current-limiting resistors need to be placed in series with each anode. This increases the number of resistors needed and can add complexity to the circuit design.

In summary, common cathode displays have the advantage of easy interfacing with microcontrollers and drivers, making them suitable for various applications. However, they require more current-limiting resistors compared to common anode displays.

Comparison

Now that we have explored the attributes of common anode and common cathode displays, let's compare them side by side:

Current-Limiting Resistors

Common anode displays require fewer current-limiting resistors since they can be placed in series with each cathode. On the other hand, common cathode displays require more current-limiting resistors as they need to be placed in series with each anode.

Multiplexing

Common anode displays are suitable for multiplexing applications, where multiple LEDs or segments are controlled using a smaller number of pins. Common cathode displays, on the other hand, are not commonly used for multiplexing.

Interfacing

Common cathode displays are easier to interface with microcontrollers and drivers since the cathodes are connected to ground. Common anode displays may require additional circuitry to interface with microcontrollers and drivers.

Voltage Requirements

Common anode displays require a negative voltage to turn off the LEDs or segments, which may be a limitation in certain applications. Common cathode displays do not have this requirement and can be easily turned off by applying a positive voltage to the anodes.

Applications

Common anode displays are commonly used in multiplexing applications, such as seven-segment displays in digital clocks and calculators. Common cathode displays are often found in battery-powered devices, such as portable digital scales and handheld multimeters.

Conclusion

Both common anode and common cathode displays have their own advantages and applications. Common anode displays require fewer current-limiting resistors and are suitable for multiplexing, while common cathode displays are easier to interface with microcontrollers and drivers. The choice between the two configurations depends on the specific requirements of the application and the available voltage sources. By understanding the attributes of common anode and common cathode, engineers and hobbyists can make informed decisions when designing electronic circuits and displays.