Analysis of LED Distributed Constant Current Technology

1. Distributed constant current technology

Distributed constant current means: an independent constant current source is set up at each parallel branch point to manage, maintain and control the stability of the branch and the overall line. Distributed constant current design LED products have very high product stability. The stability of the driving line directly affects the overall stability of the product, and distributed constant current has unique advantages. Keeping

the branch and the overall current stable, it is also necessary to be able to conveniently control and manage the branch and the overall line work, which is the scope of distributed constant current technology. Driving LEDs requires constant current, but the size of the current depends on the application environment. The intelligent development of LED lighting is the key, and distributed constant current technology fully reserves intelligent interfaces.

In the design of distributed LED drivers, drive back search, adjustable color temperature, and grayscale control must become convenient. This is the necessity of the development of distributed constant current technology. The driving voltage should be adjusted appropriately with temperature changes. Customer designs vary from product to product and the number of LEDs varies. The branch constant current balance requires feedback circuits to complete. LED is rapidly replacing CCFL as a new generation of backlight, but we found that the color rendering is not as good as CCFL, and the color temperature cannot be adjusted. It is not that we do not need the LED color temperature to be adjustable, but the key is that the design circuit does not support adjustable color temperature.

In LED applications, grayscale also needs to be well-performed. Grayscale control is always confused with brightness. In fact, there is an essential difference. Grayscale control represents the level of intelligence, while brightness is only set once in the product. Intelligence must be inseparable from grayscale reproduction. Another feature of distributed constant current technology is that the AC power supply part continues to use the traditional switching power supply and constant voltage power supply mode. The accumulation of switching power supply technology will create quality conditions for LED power supply design. Although accelerating aging to estimate the life of the power supply is a way, there is still some gap with the long-term practical technology accumulation of traditional switching power supplies! Distributed constant current also has its shortcomings. At the beginning, it will increase some design costs. Product design quality and line design selection need to be weighed. The cost increase may be short-term and superficial, and should be considered comprehensively. 2. Distributed constant current source node setting Distributed constant current technology is to connect a low-voltage difference linear constant current driver in series at the node where constant current is required. Low voltage difference is very important and is related to product driving efficiency. There are many ways to achieve constant current drive, among which low-voltage difference linear constant current can realize all LED application designs, which is stable and simple. Combined with switching power supply, it has a perfect constant current drive architecture. The placement point of the constant current source is flexible. In all parallel branches, the change of branch current will not affect the operation of other branches. Everyone hopes to select LEDs to obtain load impedance matching. Distributed constant current can be designed to be more perfect, and the requirements are not very high and can be exempted from selection. Only by keeping the current of each branch and the overall line stable can the stability of the lighting product be improved. The constant current source is placed at each parallel branch node, or it can be an overall constant current point design. The constant current source can play a good role at a certain position in the series branch. Generally, the number of constant current drive channels is difficult to match with the design, and distributed constant current will have a high degree of design flexibility. In the design of LED lighting circuits, the AC power supply needs a feedback circuit to match the number of output LED drivers and the rationality of the driving efficiency. In the distributed constant current drive source, each drive source can directly complete the optocoupler feedback task. 3. The softwareization of constant current output will open up a leap in LED application technology In the daily drive power supply design, the cumulative error of peripheral devices is very difficult to handle, and the drive power supply parameters are far from the original design intention. Constant current drive requires current detection. The usual practice is to connect a milli-resistance in series in the branch to obtain feedback information. To achieve high efficiency, the resistance value will be smaller. Too small milli-resistance will cause troubles in production and testing. General instruments cannot verify the correct value. The production process will affect the accuracy. The current value is fixed and it is very inconvenient to adjust. The softwareization of distributed constant current output will open up a leap in LED application technology. The softwareization of LED constant current technology will greatly improve the flexibility of LED applications. The softwareization of constant current driver current setting is actually very simple. Registers are set up inside the IC to set the output current size according to the actual product application storage method. All of this is a software process and does not require changes to the circuit design. When selling devices, microcomputer operation software is provided, and the circuit current setting is completed with intuitive digital writing. 0 devices around the drive circuit is our goal. 0 devices around the periphery will not bring about the accumulation of design device parameter errors. The constant current accuracy caused by the accumulation of peripheral device errors will rise to 0. 4. Driver Advantages We divide the constant current output range into several levels equally. Each level of current is digitally described and specified in a register within a certain space. When the driver IC is powered on, it will read the corresponding number and execute the corresponding current value. Built-in E2PROM is the first choice. Any register can complete its task. The type of memory is selected according to the application needs and the degree of process permission. While developing the driver technology, the application software should also be developed at the same time. The friendly interface supports digital writing technology, making the LED driver power supply design simpler and smarter. The current level division is different from the design requirements, because the models of Changyuntong Company correspond to different markets. After the distributed constant current has built-in registers, the current value division will make up for the lack of process accuracy. Due to the manufacturing process, the output current always has errors, so it is improved. The output current size can be determined when the driver IC leaves the factory, and different current output values ​​can be provided according to different customers, eliminating the batch calibration process. For small customers, rewriting the current value by attaching microcomputer software is the most convenient way. There is another situation that customers often need, such as the brightness requirements of the product, allowing different driving currents and requiring the product brightness to be consistent, so as to solve the end customer's requirements for brightness through the product design interface. After many years, due to the attenuation of LED light or according to the actual usage, the driving current value and purpose are determined again. 5. Distributed interface Distributed constant current technology requires the support of distributed communication methods, and LED intelligence must be completed with advanced communication technology. Single-line data transmission has been selected as the LED distributed technology communication method. It adopts Manchester encoding, a fixed rate of 400Kbps, a reliable communication transmission distance of more than 1 meter, and can cascade up to 1024 constant current sources. It has built-in 150℃ temperature protection and provides an optocoupler drive interface. In the distributed constant current technology, each independent constant current source can complete the optocoupler feedback. According to the constant current source pressure difference information, the optocoupler is directly driven to complete the circuit feedback process. The peripheral design is 0 devices, the power supply output voltage is matched with the load impedance, and the constant current source and light source are integrated. Shenzhen Changyuntong Optoelectronic Technology Co., Ltd. has been committed to the development and design of light sources with built-in constant current technology and built-in control technology. It adopts distributed constant current control technology and combines advanced manufacturing processes to launch a series of nominal value light source products with 24V, 36V, and 48V, so that terminal applications become simpler and simpler. 6. Analysis of the development direction of AC power supply ⑴ Primary feedback power supply It is used to drive low-power LED lamps and is transplanted from the original primary feedback charger switching power supply. This part of the AC drive has not changed its specifications due to LED applications. There are many models to choose from. Except for the limited volume, there is no essential difference in design from the switching power supply. It is reasonable to borrow and apply it to LED. ⑵ High-power isolated lighting power supply LEDs are all designed with switching power supplies. So far, no company has launched AC drive devices dedicated to LEDs. Isolation design is to design switching power supplies. The LED industry is hot and it is just for LED development. It can be basically asserted that the switching power supply is LED-AC drive, which is also one of the main application methods. ⑶ Non-isolated LED driver power supply





























































Non-isolated LED drivers have introduced more targeted power supply technologies, which is worthy of recognition and is a direction for LED power supplies. Isolation safety mainly depends on the design of creepage clearance with the shell. There is no requirement that LED power supplies must be isolated, nor is there a limit on the output voltage value. The key is which isolation safety is used. Non-isolation has advantages such as high drive efficiency, and combined with the structure, it can also design high-quality, safe, and efficient LED products.

⑷ Thyristor dimming compatible power supply

Special applications, limited quantity, and transitional arrangements.