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In the early stage, LED displays were mostly used for outdoor applications with larger pitch products. Since they were designed as static scanning drives, there was no physical space limitation for the driver IC. However, when LED displays start to be used in indoor applications and products with smaller pitches are used, the space available for electronic components is squeezed. Therefore, dynamic scan drive (line-scanning drive) based on time division multiplexing (TDM) appears . In the line scan driving mode, the LED display can be divided into two types: common cathode and common anode.
Common anode means individual LEDs are connected via their positive ends and driven by negative ends. And common cathode means individual LEDs are connected via their negative ends and driven by positive ends, and in common cathode mode, R, G, B chips are separately powered with voltage and current precisely distributed to red, green, and red diodes, and the current passes the diodes then to the negative ends of ICs.
In common anode mode, the current of the LED display flows from the PCB to the LED diode, and the RGB LEDs are powered by the same power supply at the same power rate, so the forward voltage drop will increase.
In the common cathode mode, the current of the LED display first flows through the LED diode, the R, G and B LEDs are powered separately, and then to the negative pole of the integrated circuit. The forward voltage drop is reduced and the internal conduction resistance is reduced.
The Supply Voltage
In the common anode mode, the LED display provides a unified voltage higher than 3.8V (such as 5V) for the RGB LEDs, so it consumes a lot of power.
In common cathode mode, the LED display provides separate voltages for R, G, B LEDs (2.8V for red LEDs, 3.8V for green and blue LEDs) according to actual needs. Power efficiency is higher due to this independent and precise power supply. Therefore, as less electricity is consumed, less heat is generated.