Energy saving analysis of LED display screen using D5026A

　D5026A is a driver IC designed by Shanghai Debei Electronics for energy-saving LED display screens. Its design concept is energy-saving and compatible with existing solutions, that is, it can be used for energy saving and compatible with traditional solutions. After calculation and testing, the display screen made with D5026A can save up to 30% of electricity. The following is a brief introduction to the energy-saving principle of D5026A.

　　Figure 2

　　As we all know, LED drivers usually use constant current source drive mode. Figure 1 is the traditional 5026 drive output structure, and Figure 2 is the constant current principle of each unit. Its constant current output current Io= Vr/Rf. In this output mode, the output voltage Vo is composed of the voltage drop Vr on Rf and the voltage drop Vds1 on the output tube A1, that is, V.=Vr+ Vds1. In the constant current state, Vds1 changes with the load. When the output current is constant, when we reduce Vo, there will always be a point that makes Io exit the constant current state. This point is called the minimum output voltage Vomin. It is not difficult to see that when V.- Vds1 is lower than Vr, the output will not be constant current. At this time, Vds1 is about 0.1V, and the minimum output voltage is Vomin=Vr+0.1(V).

　　Figure 3 is the D5026A drive output structure, and Figure 4 is the constant current principle of each unit. D5026A adopts the working principle of the mirror constant current source. Its output current Io is completely proportional to the area of ​​the two mirror tubes, that is, Io=Ir x (Sa1/Sb1). Sa1/Sb1 is determined during the IC layout design, so the consistency can be very good.

　　Comparing Figure 4 with Figure 2, it is obvious that Vo=Vds at this time, completely omitting the voltage drop on the feedback resistor Rf. However, the voltage drop on the feedback resistor accounts for a large proportion here. This is because if the voltage drop of the feedback resistor is set too low, it is difficult to compensate for the error caused by the feedback amplifier offset, and the consistency of the constant current source is difficult to guarantee. Usually the voltage drop of the feedback resistor is about 400mV-600mV. In other words, under the same conditions, the minimum output voltage Vomin of D5026A is 400mV-600mV lower than that of the traditional 5026.

　　Let's take the blue light as an example. Assuming the on-voltage of the blue light is 3.2V, without considering factors such as line loss, the minimum power supply voltage of the traditional 5026 is Vc=3.2+0.4(0.4-0.6)+0.1=3.7V (or even 3.9V). The D5026A can work at Vc=3.2+0.1=3.3V. Of course, the above considerations are ideal conditions. If factors such as line loss and power supply fluctuations are taken into consideration, we recommend that the power supply voltage be selected between 3.6V-3.8V.

　　We have calculated that if the existing 5V power supply display screen is changed to a 3.8V power supply display screen, 24% of electricity can be directly saved without any changes in the circuit, structure, or control. In the past, the saved electricity was applied to the 5026, which caused the 5026 to operate at an extremely high temperature, greatly reducing the reliability of the drive circuit. If the D5026A is used, the power consumption of the drive circuit will be greatly reduced, and the temperature rise will be extremely insignificant, which saves electricity and improves the reliability of the device, while greatly reducing the consideration of heat dissipation during structural design. Under exactly the same conditions, the surface temperature of the 5026 of a certain model of display screen powered by 5V is 73 degrees, while the surface temperature of the D5026A powered by 3.8V is only 39 degrees. Obviously, the advantages of using the D5026A are self-evident.