Analysis of the Principle of Energy-Saving LED Display

The energy-saving concept of LED display screens has quietly become a highlight that attracts consumers' attention and is also the reason for its explosive growth in recent years. Of course, after the crazy growth in recent years, the industry is now in a deadlock and in a dilemma of reshuffle. In this dilemma, many companies will inevitably be seriously injured and even go bankrupt. Of course, many companies will also come out of the haze and achieve more long-term development. This is the law of industry development. No company can escape this disaster. How to be reborn in the disaster is a problem that every company is currently concerned about.

In this era of high calls for energy conservation, further energy conservation of LED displays has become the support point pursued by the industry. Many companies have made various improvements in this regard, and have achieved energy conservation to a certain extent. However, there is still a long way to go to achieve greater energy conservation, which requires the joint efforts of the entire industry.

Recently, a few energy-saving LED displays have appeared on the market. The improvement of the power supply has greatly improved the energy-saving effect of LED displays, which has attracted the attention of many consumers and given them high expectations. Many LED display manufacturers are eager to try and are ready to introduce this technology first to gain development opportunities. Based on the current technology, how is the energy-saving effect of energy-saving LED displays achieved?

Let's use a small LED module to analyze its power consumption! As shown in Figure 2, it is a small LED module with CYT62726 launched by Changyuntong Optoelectronics as the driver chip. Its power supply voltage is 5V. The power consumption of peripheral devices is not calculated first, because they account for a very small proportion of the entire screen. The power consumed by the entire screen is all on the lamp. First calculate the lamp power as Pled=n*Uvf*Iled (n is the number of channels, Uvf is the voltage drop of the LED lamp, and Iled is the set current value). The pin voltage drop of CYT62726 driver IC is generally around 0.6V, and the voltage drops of red, green and blue lamps are 1.8V, 3.0V, and 3.0V respectively. In this way, each channel only needs 4V (3.0+0.6V) to work normally. It can be conservatively set to 2.8V for the red light channel and 3.8V for the blue and green channels. In fact, our power supply voltage is 5V, which is equivalent to adding 1V*Iled. The power consumption is inside the IC, so as above, it can be imagined that only

If we reduce the power supply to 2.8V for red, 3.8V for green and 3.8V for blue, we can save the 1V*Iled power consumption added to the IC channel. With other components unchanged, the LED display can save at least 15% of energy. In addition, the reduction in the heat dissipation requirements of the LED screen can also achieve a certain degree of energy saving. This is already a considerable number for a large screen, and I believe customers will be happy to accept it!

We can further analyze its energy-saving principle!

First of all, from the perspective of power supply, as shown in Figure 3, which is a traditional switching power supply schematic, if 5V is to be reduced to 4V, the proportion of the output voltage occupied by the rectifier Schottky forward voltage drop will inevitably increase. The lower the output voltage of the switching power supply, the lower the power output efficiency will be, because the proportion of the rectifier Schottky forward voltage will be higher (its proportion X = V voltage drop / V output, the output is reduced from 5V to 4V, and its voltage drop is 0.5V, then its proportion will increase from 0.1 to 0.125, an increase of 25%), which is not obvious for the overall energy saving effect of the LED screen, so it is obvious that the use of this power supply design principle cannot achieve the improvement of the power supply working efficiency. At the same time, 5V is the nominal value voltage, which is quite mature in market application. Enabling a new switching power supply voltage will only increase costs while reducing efficiency, and the quality is difficult to guarantee, which is difficult to achieve.

The design of power supply is a relatively mature field. Another design idea can be used to realize the power supply of the display screen, such as synchronous rectification technology. The basic principle is shown in Figure 4. Q10 is a power MOSFET. In the positive half cycle of the secondary voltage, Q10 is turned on and Q10 plays a rectifying role; in the negative half cycle of the secondary voltage, Q10 is turned off. The power loss of the synchronous rectification circuit mainly includes the conduction loss of Q10 and the gate drive loss. When the switching frequency is lower than 60KHz, the conduction loss is dominant; when the switching frequency is higher than 60KHz, the gate drive loss is dominant. When driving a relatively high-power synchronous rectifier, when the gate peak drive current IG (PK) is required to be ≥ 1A, a CMOS high-speed power MOSFET driver can also be used. After synchronous rectification replaces Schottky rectification, the proportion of consumption in the output power can be effectively reduced. The use of synchronous rectification technology is necessary.

在选择AC/DC开关电源时，可以选用半桥或全桥新技术，这样可以使开关电源效率提升到90%以上。当然这些技术应用，给led显示屏供电是可以将电压降至最佳状态，同时电源的效率也能达到高效率水平，因此采用新的电源技术给led显示屏供电是可以达到显著节能的效果。电源成本也肯定会有一些增加，

Secondly, we can carefully study the LED screen driver IC. As shown in Figure 5, the output end is a MOS switch tube (as shown in Figure 6), which controls the output port to be turned on or off. The output port voltage drop is VDS = about 0.65V, which is determined by the process and materials. To reduce VDS to 0.2V or even 0.1V, the required area must increase. In the structure of the MOS tube, it can be seen that there is a parasitic capacitance between GS and GD, and the driving of the MOS tube is actually the charging and discharging of the capacitor. This charging and discharging process takes a period of time. If the area increases, the parasitic capacitance on the MOS tube will also increase. In this way, the consequence is that the port response speed of the entire IC decreases, which will be a fatal weakness for an LED screen driver IC. Therefore, if you want to start from the IC, reduce the transition voltage, and make the driver IC have enough response speed, the decisive factor is the process, which is difficult to achieve. Some people think that other design principles can be used, but if it is constant

For flow ICs, the internal circuits may be different, but the switch tube at the channel port must exist, so even if other design principles are used, it is difficult to achieve the purpose of voltage reduction.

综上所述，led节能显示屏的实现主要是从供电电源上着手，在现有的LED显示屏上直接采用半桥或全桥高效率开关电源，再加上同步整流节能效果显著。给驱动IC恒流的状态下尽量的减小电源电压，通过红绿蓝各管芯分开供电来达到更好的节能效果。当然这种非标准电压电源和新技术的应用成本必然有所上升。从屏幕驱动IC上看，节能并不明显，减小驱动恒流压差还会带来包括成本在内的新的问题。部分IC企业宣传驱动节能设计，无非是出于销售策略而已。