The D5026A is a driver IC designed by Shanghai Debe Electronics specifically for energy-saving LED displays. Its design philosophy prioritizes energy efficiency while maintaining compatibility with existing solutions; in other words, it can be used for energy saving while remaining compatible with conventional solutions. Calculations and tests have shown that displays made with the D5026A can save up to 30% or more in power. Below is a brief introduction to the energy-saving principle of the D5026A.
As is well known, LED drivers typically employ a constant current source driving mode. Figure 1 shows the traditional 5026 driver output structure, and Figure 2 illustrates the constant current principle of each unit. The constant current output current is Io = Vr/Rf. In this output mode, the output voltage Vo is composed of the voltage drop Vr across Rf and the voltage drop Vds1 across the output transistor A1, i.e., V<sub>o</sub> = Vr + Vds1. In constant current mode, Vds1 varies with the load. When the output current is constant, decreasing Vo will eventually cause Io to exit the constant current state; this point is called the minimum output voltage Vomin. Combining Io = Vr/Rf with V<sub>o</sub> = Vr + Vds1, it's easy to see that when V<sub>o</sub> - Vds1 is lower than Vr, the output will not be constant current. At this point, Vds1 is approximately 0.1V, so the minimum output voltage is Vomin = Vr + 0.1 (V).
Figure 3 shows the output structure of the D5026A driver, and Figure 4 shows the constant current principle of each unit. The D5026A adopts the working principle of a mirror constant current source. Its output current Io is directly proportional to the area of the two mirror transistors, i.e., Io = Irx(Sa1/Sb1). Since Sa1/Sb1 is determined during IC layout design, the consistency can be very good.
Comparing Figure 4 and Figure 2, it's clear that Vo = Vds in this case, completely omitting the voltage drop across the feedback resistor Rf. However, the voltage drop across the feedback resistor accounts for a significant portion of the overall voltage. This is because if the feedback resistor voltage drop is set too low, it's difficult to compensate for the error caused by the feedback amplifier's offset, making it hard to guarantee the consistency of the constant current source. Typically, the feedback resistor voltage drop is around 400mV-600mV. In other words, under the same conditions, the D5026A's minimum output voltage Vomin is 400mV-600mV lower than that of the traditional 5026.
Taking a blue LED as an example, assuming its on-state voltage is 3.2V, and disregarding factors such as line loss, the minimum power supply voltage for a traditional 5026 LED is Vc = 3.2 + 0.4(0.4 - 0.6) + 0.1 = 3.7V (or even 3.9V). The D5026A, however, can operate at Vc = 3.2 + 0.1 = 3.3V. Of course, the above considers ideal conditions. If line loss and power fluctuations are taken into account, we recommend a power supply voltage between 3.6V and 3.8V.
We have calculated that replacing the existing 5V powered display screen with a 3.8V powered one would directly save 24% of power without any changes to the wiring, structure, or control. Previously, this saved energy was used on the 5026 chip, causing it to operate at extremely high temperatures and significantly reducing the reliability of the drive circuit. Using the D5026A significantly reduces power consumption in the drive circuit, with minimal temperature rise, saving energy, improving device reliability, and greatly reducing the need for heat dissipation considerations in the structural design. Under identical conditions, the surface temperature of the 5026 chip in a certain model of display screen using 5V power is 73 degrees Celsius, while the surface temperature of the D5026A using 3.8V power is only 39 degrees Celsius. The advantages of using the D5026A are obvious.
