One article and one picture to understand the classification of mainstream LED lighting driver technologies

LED lighting drive technology has developed to the point where multiple solutions are being developed in parallel in the industry. This article mainly discusses dimmable LED lighting drive technology. To summarize all dimmable solutions, if divided from the topology, they can be classified into two-stage AC/DC conversion LED current drive solutions, single-stage AC/DC conversion LED current drive solutions, and linear AC/DC conversion LED current drive solutions; from the dimming control interface, they can be classified into phase-cut dimming LED current drive solutions (also known as thyristor dimming LED current drive solutions) and smart interface dimming LED current drive solutions (mainly divided into I2C interface dimming and PWM interface dimming). Smart interface control signals can be divided into ZigBee, Bluetooth, and Wi-Fi chip related interfaces.

To summarize, the relevant classification of LED lighting driving technology can be seen in Figure 1.

Figure 1: LED dimming topology and dimming control classification

The evolution of dimmable solutions

The two-stage AC/DC conversion LED current drive solution was once widely accepted by the industry due to its good performance and no output current ripple, but this solution is too expensive. After Marvell successfully launched the superior single-stage AC/DC conversion LED current drive solution EM8183 in 2012, the two-stage AC/DC LED current drive solution was gradually abandoned by the industry. On the other hand, the linear AC/DC conversion LED current drive solution has been discussed in the technical field and has existed in the industry for nearly ten years. This solution has never been accepted by the industry because of its current ripple and flicker index that cannot be overcome during phase-cut dimming. At present, the single-stage AC/DC conversion LED dimming current drive solution has become the mainstream of LED dimming solutions due to its superior cost performance. Here we mainly discuss the phase-cut dimming and intelligent interface dimming solutions of single-stage AC/DC conversion LED current control.

Single-stage AC/DC conversion current control scheme

The key to phase-cut dimming (thyristor dimming) is that the LED driver can provide sufficient latching current and holding current at any operating point. Sufficient latching current and holding current are the physical conditions for the thyristor to meet normal operation. On this basis, the performance of the LED driver must ensure accurate current control, sufficient dimmer compatibility, smooth dimming curve, sufficiently wide dimming range, and sufficiently low flicker index. The reliability of the LED driver must ensure high efficiency, sufficiently low heat loss, no prominent hot spots, and a sufficiently long product life cycle. In addition, minimizing the audio noise when the LED driver is working is also one of the keys to the success of the product . In these aspects, the industry has many related patent technologies. Among them, Marvell has more than 70 US and international patents in this field to ensure product performance while protecting the interests of the company and customers .

As the industry's first single-stage AC/DC conversion LED current control solution, Marvell successfully launched the superior performance phase-cut dimming LED driver chip EM8183 in 2012. The driver chip was accepted and adopted by leading companies in the LED lighting field at the initial stage of its launch in the industry. The EM8183 LED driver chip has brought huge benefits to related companies and customers, promoted technological development and innovation in the lighting field, and established its classic position in the industry in the innovation of phase-cut dimming. Following EM8183, Marvell launched the second-generation phase-cut dimming LED driver chip EM8187 in early 2014. Based on EM8183, this driver chip improves the performance in dimmer compatibility, efficiency and EMI, and reduces the cost of the system. EM 8187 applies a number of Marvell patented technologies to improve its performance in compatibility, heat loss control, efficiency, and dimming performance. Figure 2 is a reference circuit board diagram of the EM8187 single-stage phase-cut dimming solution. The EM8187 requires very few peripheral components and provides extremely high reliability and excellent cost-effectiveness for the entire system.

Figure 2: Reference circuit board diagram of single-stage phase-cut dimming system

Figure 3: Reference circuit board diagram of single-stage intelligent dimming system

Smart dimming performance gradually improves

In terms of LED intelligent dimming technology, the industry has mainly chosen the cost-effective single-stage AC/DC conversion drive solution at this stage, and the choice of LED intelligent dimming interface mainly includes I2C interface and PWM interface. Because only one interface control signal is required, the PWM interface has the characteristics of simple connection, which is also conducive to software implementation. However, under the working state of low-end luminous flux, the PWM interface dimming solution usually has the phenomenon of step dimming, which is commonly known as the low-end step dimming problem. This is caused by insufficient PWM accuracy or insufficient matching of hardware and software. I2C interface intelligent dimming requires two connection signals. I2C intelligent dimming can achieve superior performance and smooth low-end light output. More importantly, in addition to dimming control, the I2C interface also provides data collection and transmission functions, which can realize and provide basic functional units for cloud access of LED lighting. Marvell launched the industry's first I2C interface single-stage AC/DC conversion driver solution EM8189 in January 2014.

The EM8189 I2C interface single-stage intelligent dimming solution can achieve 1% dimming accuracy, smooth dimming performance, low standby power consumption (< 250mW) and excellent overall cost performance. The EM8189 IC can connect to ZigBee, Bluetooth, and Wi-Fi interfaces and provide an excellent intelligent dimming system with related software. After its launch, the EM8189 was evaluated by the American Index Lighting Company as the first choice for intelligent dimming and launched related products. Figure 3 is a reference sample of the EM8189 intelligent dimming solution, from which it can be seen that the EM8189 intelligent dimming solution has very few peripheral devices. This provides a basic guarantee for the cost performance and reliability of the final dimming product. Figure 4 is the dimming performance curve of the EM8189 intelligent dimming solution. From Figure 4, it can be seen that the EM8189 intelligent dimming solution has excellent linear performance and a high degree of overlap from high end to low end and from low end to high end. With the relevant software design, it can achieve any dimming curve required by customers from linear dimming to exponential dimming.

Figure 4: Dimming performance curve of the EM8189 intelligent dimming solution

LED lighting has gone through several stages of technological innovation and reorganization, and this trend will continue to develop until saturation. At the same time, there are still several problems to be solved in LED driving technology, including EMI, noise and reliability; there are still several aspects of product performance that need to be improved, including compatibility, efficiency, product discreteness, etc.; LED lighting will continue to improve the overall lighting effect, and the cost will be further reduced. Of course, no matter which aspect is successful, it depends on the efforts to break through the control technology and the innovation of manufacturing technology. These urgently need more LED lighting related companies to give full play to their strengths and jointly lead the new trend of technological innovation and market application.

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