The energy-saving concept of the LED display has been quietly raised, which has become the most bright spot that attracts the attention of consumers, and is also the reason for its explosive growth in recent years. Of course, after crazy growth in recent years, the industry is currently in a stalemate to reshuffle the dilemma. In this dilemma, there are bound to be many companies that are seriously affected by this impact and even go bankrupt. Of course, many companies will get out of the haze and get more long-term development. This is the law of development of the industry. No enterprise can escape this disaster, and how to rebirth in the disaster is a current concern of every enterprise.
In this era of extremely high energy-saving demand, the further energy-saving of LED display screens has become the support point of this industry chase. Many companies have made various improvements on this point, to a certain extent, to achieve energy-saving effects, but to achieve greater energy saving, there is still a long way to go, which requires the common industry Work hard.
Recently, there are few energy-saving led displays on the market. The improvement of the Power Supply has greatly improved the energy-saving effect of led displays, attracting the attention of many consumers and giving them very high expectations. , Many LED display manufacturers are eager to try, ready to introduce this technology first, gaining development opportunities. On the basis of the current technology, how does the energy-saving effect of energy-saving led display screen be realized?
We use a small led module to analyze its power consumption! As shown in Figure 2, it is a small LED module with CYT62726 as the driver chip launched by Changyun Optoelectronics. Its power supply voltage is 5V, and 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 on the lamp, first calculate the lamp power Pled = n * Uvf * Iled (n is the number of channels, Uvf is the voltage drop of the LED lamp, Iled is the set current value) CYT62726 driver IC The voltage drop of the pin is generally about 0.6V, the voltage drops of the red, green and blue lights are 1.8V, 3.0V, 3.0V. So each channel only needs 4V (3.0 + 0.6V) to work normally, be conservative It can be 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 increasing the power consumption of 1V * Iled inside the IC, so as above, it can be assumed that as long as the power supply is reduced to Red 2.8V, green 3.8V, blue 3.8V, we can save the 1V * Iled power consumption added to the IC channel, and can achieve at least 15% more energy saving in the led display when other devices are unchanged. In addition, the reduction of the heat dissipation requirements of the LED screen can also achieve a certain degree of energy saving, which is Big screen is already a considerable figure, I believe customers will be happy to accept!
We can further analyze the principle of energy saving!
First of all, from the perspective of the power supply, as shown in Figure 3 is a schematic diagram of a traditional Switching Power Supply. If 5V is to be reduced to 4V, the proportion of the output voltage of the rectifier Schottky forward voltage drop will inevitably increase. , The higher the proportion of the forward voltage of the rectifier Schottky (the specific gravity X = V voltage drop / V output, the output is reduced from 5V to 4V, and the voltage drop is added to 0.5V, the specific gravity will increase from 0.1 to 0.125, increase 25%), the lower the output efficiency of the power supply, which is not obvious for the overall energy saving effect of the LED screen, so it is obviously impossible to improve the working efficiency of the power supply using this power supply design principle. At the same time, 5V is the nominal value voltage, which is quite mature in market application. Enabling the new switching power supply voltage will reduce the efficiency while only increasing the cost, and the quality is difficult to guarantee and it is difficult to achieve.
The design of the power supply is a relatively mature field, and another design idea can be adopted to realize the power supply of the display, such as synchronous rectification technology. The basic principle is shown in Figure 4. Q10 is a power MOSFET. During the positive half cycle of the secondary voltage, Q10 is turned on and Q10 plays a rectifying role. During the negative half cycle of the secondary voltage, Q10 is turned off. The power loss of the synchronous rectifier circuit mainly includes Q10. Conduction loss and 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 higher power synchronous rectifier, when the peak gate drive current IG (PK) ≥ 1A is required, a CMOS high-speed power MOSFET driver can also be used. After synchronous rectification replaces Schottky rectification, it can effectively reduce the proportion of output power consumed. It is necessary to use synchronous rectification technology.
When choosing AC / DC Switching Power Supply, you can choose half-bridge or full-bridge new technology, so that the efficiency of switching power supply can be improved to more than 90%. Of course, with these technical applications, powering the LED display can reduce the voltage to the optimal state, and the efficiency of the power supply can also reach a high efficiency level. Therefore, the use of new power supply technology to power the LED display can achieve a significant energy saving effect. There will certainly be some increase in the cost of power supply,
Secondly, we can carefully study the LED screen driver IC. As shown in Figure 5, the output terminal is a MOS switch tube (as shown in Figure 6), which controls the output port to be turned off or on. This is determined by the process and materials. To reduce VDS to 0.2V or even 0.1V, the area required by itself must be increased. 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 charging and discharging the capacitor. This charging and discharging process takes some time. If the area increases, the parasitic capacitance on the MOS tube will also increase, so the consequence is that the port response speed of the entire IC decreases, which is for an LED screen driver IC It will be a fatal weakness. Therefore, if you want to start with the IC, lower the corner voltage, and at the same time make the driver IC have a sufficient response speed. The process is the decisive factor, which is difficult to achieve. Some people think that other design principles can be used, but if it is a constant current IC, the internal circuit may be different, but the switch tube of the channel port must exist, so even if other design principles are used, the purpose of voltage reduction is also Difficult to achieve.
In summary, the realization of the LED energy-saving display mainly starts from the power supply, and the half-bridge or full-bridge high-efficiency switching power supply is directly used on the existing LED display, and the synchronous rectification energy-saving effect is remarkable. Reduce the power supply voltage as much as possible in the state of constant current for the driver IC, and achieve a better energy saving effect by separately supplying power from the red, green and blue dies. Of course, the application cost of such non-standard voltage power supplies and new technologies is bound to rise. From the point of view of the screen drive IC, energy saving is not obvious, and reducing the driving constant current pressure difference will also bring new problems including cost. Some IC companies publicize and drive energy-saving designs only because of sales strategies.
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