In 2013, we felt the warmth of the LED industry. There are currently several trends that are driving the development of the LED lighting market. The first is the continuous improvement of the efficiency of high-brightness LEDs and the continuous emergence of high-efficiency and high-reliability constant-current LED drive power, and the second is the global legislation prohibiting the gradual fading of incandescent lighting and CFL energy-saving lamps (it contains mercury that is harmful to the environment). The combination of these factors is making LED lighting a long-term development trend. More importantly, low cost (including LED lamp beads, heat dissipation system and LED driver) is the original driving force for consumers to widely adopt LED general lighting. In addition to the major mission of energy saving and emission reduction, the more controllable characteristics of LEDs than other light sources make it possible to revolutionize people's light environment and provide many novel worlds of light and shadow. The most critical link to realize these applications is the drive: the brain of the LED light source. Smaller size, fewer components, lower cost, more powerful, these are the "harsh" requirements for LED drive power. This minimalist line 18W LED fluorescent lamp driving solution introduced in this article has a size of less than one dollar coin, and the cost is about half of the current mainstream solutions in the market, which is born to comply with this "harsh" requirement. The philosophy of simplicity or perfection is brought into full play in this scheme. 2.1 Introduction to the third-generation non-isolated LED constant current control technology closed-loop algorithm TRUEC2 Aiming at the characteristics of LED lighting load, the topology of the current non-isolated constant current drive power supply is basically the Buck Buck structure. The development of non-isolated LED constant current control technology is divided into three generations, from the initial fixed frequency mode to the later fixed off-time mode, strictly speaking, it is not a true closed-loop constant current, and it has been developed to the present day. Closed-loop algorithm of non-isolated control technology, called TRUEC2 control strategy. The DU8618 chip of Shanghai Duty Cycle Semiconductor Co., Ltd. is based on TRUEC2 drive technology and is insensitive to various peripheral components. This improves reliability and accuracy while reducing the cost of the overall solution. The so-called closed loop is to actually detect the output current value and use this as a standard to send out a PWM signal. The so-called open loop does not use the detected output current value as a reference to issue a PWM signal. From the circuit topology, there is no difference between the two, both are non-isolated BUCK buck topology. But there are two benchmarks inside the chip, one is the peak benchmark and the other is the average benchmark. The chip detects the inductor current signal and processes it with a patented technology, as shown in Figure 1 TRUEC2 part for integration processing and peak control. In this way, the average value of the inductor current is detected, which is the average value of the output current. Based on the detected value, the chip controls the output duty cycle to achieve closed-loop control. This control structure makes the circuit extremely simple. Due to the closed-loop control current, compared to the open-loop mode, this circuit is also short-circuited at a constant current. This is very important in production applications, which is equivalent to greatly reducing the risk of system failure. This solution not only has a qualitative leap in performance, but also greatly improves reliability. The DU8618 integrates 1A high-voltage MOSFET, which will simplify the circuit to the extreme. Through low-current and high-voltage design, it reduces losses, so that the 1A MOSFET is integrated into a small-sized SOP8, which can handle all non-isolated LED drivers within 18W demand. Figure 1: Working diagram of some TRUEC2 modules inside the chip 2.2 DU8618 integrated switch simplifies the circuit to achieve full closed loop 18W LED fluorescent lamp constant current control DU8618 is a chip based on TRUEC2 technology, specially used for driving 18W LED non-isolated fluorescent lamp. The basic electrical parameters are as follows: Input voltage range: 180 ~ 265VAC / 50Hz Typical efficiency: "95% Output voltage range: 60 ~ 180VDC output current: 90mA Nominal output power: 18W Figure 2: Full closed loop non-isolated buck constant current 18W LED fluorescent lamp driving power schematic Figure 3: DU8618 output 18W non-isolated LED fluorescent lamp driving power supply size schematic Figure 4: PCB layout The schematic in Figure 2 shows that to achieve an output power of 18W, all the components required for the solution are only 14. The visual displays in Figures 3 and 4 show that the scheme is less than one dollar coin. The advanced control methods described above are the fundamental reason for achieving higher power density. The practical significance is not only to increase the power density. The technological advancements also include: simpler circuits, lower costs, and higher constant current accuracy. The efficiency of 95% is higher than most of the solutions in the market. The design idea of ​​small current and high voltage is the key to achieving such high efficiency.
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