Before discussing the LED display system, knowing about the basic concept of LED and LED driver structure is necessary.

There are two kinds of RGB LED shown in Figure 2-1 and Figure 2-2, common anode and common cathode. Common anode LED means the anodes of LED are tight together, and vice-versa for the common cathode. Note that LED forward voltage varies by color. Typically, 1.8V to 2.2V for red LED and 2.8V to 3.4V for blue/green LEDs.

Figure 2-1 Common Anode LED

Figure 2-2 Common Cathode LED

So, when talking about LED drivers, there is common anode or common cathode LED driver, as the driver architectures shown in Figure 2-3 and Figure 2-4. Traditionally, common-anode LED driver is more common due to the sink driver with NMOS structure which has lower cost than that of source driver with PMOS structure. While now common-cathode LED driver is more popular due to saving power.

The biggest difference between them is that common-anode LED driver has only a single rail for all RGB, but common-cathode LED driver has 2 split rails. One is for red LED and another is for green and blue LEDs.

Common cathode LED driving method can significantly save power because the red LED has much lower forward voltage than that of green and blue LEDs. In addition, LED display surface temperature reduces more than 10 degrees and has better color uniformity and longer LED life. Usually, the total power consumption can be reduced by 30% to 75%.

Figure 2-3 Common Anode LED With Sink Driver Architecture

Figure 2-4 Common Cathode LED With Source Driver Architecture