The accuracy of the LED drive is usually considered constant current error, in fact, the drive accuracy is not limited to a current accuracy. The LED is a typical current-driven device that precisely controls the LED drive current and can determine many parameters including light efficiency, power efficiency, heat dissipation, and product brightness. The main driver LED is to control its current. Whether it is directly increasing or decreasing the drive current or the duty cycle (PWM) reducing the switching time ratio, it is a control current method, but the purpose of achieving is not the same. This article will explain the differences between different drivers in different applications.
Distributed constant current driving principle
In the past, in the incandescent and energy-saving lamp market, it is very difficult for LEDs to continue to comply with mainstream models with limited specifications formed by large companies. LED has its application flexibility, will bring more power specifications in the future design. We must avoid excessive power supply specifications and do not bring many obstacles to future production. In line with the idea of ​​not limiting the design flexibility while still taking into account the minimum power supply design specifications, we have proposed a distributed constant current architecture.
The principle of distributed constant current is to set up an independent constant current source at each parallel branch point to manage, maintain, and control the stability of branches and branches, branches, and overall lines. The distributed constant current circuit can be regarded as a complete line structure in use, and the practical application is distributed in each node of the line, it is a circuit structure that can control through constant current and can communicate with each other. Distributed constant current design LED products have very high product stability and unique design advantages.
At present, LED products claim to have a large gap with actual service life. Given the limited accumulation of driveline design techniques, the actual service life can be measured by the method of evaluating product life, which can easily cause errors. The stability of the drive line will directly affect the overall stability of the product.
The reason why the distributed constant current technology has high reliability is that the AC power supply part continues to use a conventional switching power supply and adopts a constant voltage power supply mode. The accumulation of switching power supply technology will create quality conditions for LED power supply design. With the same power supply and power specifications, no new power supply models can be developed, and the power can be downwardly compatible, which greatly reduces power supply specifications and improves power supply uniformity.
Soft and hard combination of precision control ideas
In the daily driving power design, the accumulated error of the peripheral devices is very difficult to deal with, causing the driving power parameters to be far from the original intention of the design. Constant-current drive requires current detection. Usually, serial resistors are connected in series in the branch to obtain feedback information. In order to achieve high efficiency, the resistance value will be smaller. Too small a resistor may cause inconvenience in production and testing. The general instrument can not verify the correct value, the production process will also affect the accuracy, the resistance mode setting current is a fixed mode, the adjustment is not convenient.
The combination of hardware and software will open the leap of LED application technology. The constant value of LED constant current software can greatly increase the flexibility of LED applications. The constant current driver current setting software is actually setting up a register in the IC. The output current is set according to the actual product application storage mode. All of this is a software process and does not require changing the circuit design. The circuit current setting can be done with an intuitive digital write through the microcomputer operating software.
Driving zeros around the line is our goal. The peripheral zero devices will not bring about the error accumulation of the design device parameters, thereby greatly improving the accuracy of the constant current.
China's IC manufacturing process currently can not meet the LED drive accuracy requirements, but we can use new technologies and new methods to achieve the world's top constant current accuracy level. Driving precision control is one of these methods.
In the precise control of driving, first of all, what is the purpose of the design? Is it based on the highest light efficiency, or is it consistent with the design of the lamp? If it is limited to the precision of the drive current, it is actually very easy to do. For example, the drive current is stable and accurate, or there is protection with changes in temperature. However, it is not limited to these customers. The customer requires that all parameters meet the requirements, such as product consistency and efficiency.
For these requirements of customers, we need to work hard on the design of the drive. In the final analysis, how to control the accuracy and ultimately adjust the current according to our design intent to improve the stability of the product.
In order to achieve the above-mentioned goal, we can divide several levels evenly within the range of refined constant current output, and describe the current of each level digitally, drive the IC to read the corresponding number and execute the corresponding current
The value is achieved. The built-in non-volatile E2PROM can be selected. It is believed that any register can complete its task, and the type of memory can be determined according to the application requirements and the conditions allowed by the process.
The division and design of the current ladder may differ from one market to another. After distributed constant-current built-in registers, the current value division will make up for the lack of precision in the process. Due to the manufacturing process, the output current always has errors, which will improve after softwareization.
Chang Yuntong's driver ICs can provide different current output values ​​according to customers' different requirements when they leave the factory, eliminating the need for batch calibration. A small amount of customers can also modify the current value by using the supplied microcomputer software. In addition, the customer can also change the brightness of the product according to the demand through the product design interface, and after a long time, again determine the driving current value and use due to the LED light attenuation or according to the actual use.
New Design Method to Improve Drive Efficiency
It is feasible for AC power to drive LEDs in a single string, but single string is only a small part of LED driver applications, and most applications have parallel conditions. In the case of a parallel LED driver, the branch LED in the overall constant current design does not necessarily work in a constant current state, and the LED current of the entire product influences each other. In general, parallel use is preferred in low-current designs because low-current products are not immediately damaged, but the risks remain.
In high-current designers, such as LED street lamp designs, designers do not directly connect multiple LEDs in parallel because the danger will occur immediately. The usual practice is to first establish constant voltage and then DC constant current, which is accomplished through these two levels of design. We know that DC drive efficiency is under reasonable voltage and load conditions. How can we ensure that the number of load LEDs or LED changes within a reasonable range of temperature? How to flexibly allow customers to change the number of LED drivers? To solve the above problems, it is necessary to design a feedback mechanism of AC to DC constant current, but so far it does not have this technical condition.
Chang Yuntong has adopted another approach: The company's distributed constant-current drivers can provide optocoupler drive capability, in which one branch can serve as a representative of all branches. The distributed constant current branches can communicate with each other, implement an adaptive linkage mechanism, and are compatible with control and data read/write interface functions. In addition, the peripheral design is zero-device and the output voltage of the power supply is matched with the load impedance, thereby realizing the integration of the constant current source and the light source.
Maidi Heating And Refrigerating Equipment Co., Ltd. , http://www.lydccompressor.com