[Text / "High-tech LED - Technology and Applications" September issue] Science and technology are advancing with each passing day, and science and technology create a new life for mankind. In recent years, the global human consensus: the future of the industry related to green environmental protection and energy conservation is bright. The LED lighting industry is the first to bear the brunt of the infinite vitality and huge mass market. In 2012, the LED lighting industry was hardly affected by the global economic crisis. With the vigorous promotion of governments, the LED lighting industry is developing rapidly. The LED lighting industry chain has grown and improved rapidly during this economic crisis. The new generation of LED lighting technology has developed rapidly. Millions of companies in the LED lighting industry chain are thriving.
The basic structure of LED lighting is: LED lamp beads + drive power + luminaire metal / plastic structural parts (Figure 1). LED lamp beads involve the brightness, color and light decay of LED lamp products; the driving power source relates to the electrical performance and stability, reliability and life of LED lamp products; the metal/plastic structural parts involve the heat dissipation performance and fashion novelty of LED lamp products, and Different applications.
Figure 1 The basic architecture of LED lighting 
With the continuous improvement of the efficacy of LED lamp beads and the continuous reduction of cost, LED lighting has entered the indoor general illumination from public lighting and decorative lighting. The biggest feature of indoor general lighting is the large quantity and low price. For example, an LED light source that directly replaces an incandescent lamp and a fluorescent energy-saving lamp, the lumen number is mainly between 200 LM and 810 LM, and the power of the corresponding LED light source is about 3 W to 10 W.
Figure 1 The basic structure of LED lighting In 2012, the price of LED lamps and lanterns of international manufacturers has entered below RMB 1/W. How to reduce the cost of driving power sources in LED light sources has become an important issue in the development of LED lighting. How to make the performance of the LED driver power supply meet the needs of LED lighting fixtures, and the cost can be controlled, the high-performance LED power supply driver chip is the key. We will discuss the driving power technology of several LED light sources currently under development.
First, flyback isolation LED drive power technology The flyback-isolated LED driver power supply with feedback from the primary side is recommended for use in LED lighting replacement lamps. Its application circuit is relatively simple and takes up less space. The typical circuit is shown in Figure 2. It uses a flyback high-frequency transformer to isolate the input and output loops. A typical high-frequency transformer consists of a primary winding NP, a secondary winding NS, and an auxiliary winding NAUX. The primary winding NP stores energy when the MOSFET is turned on, and the secondary winding NS supplies current and energy to the LED and the output capacitor when the MOSFET is turned off, and the auxiliary winding NAUX usually realizes secondary winding demagnetization detection (current zero crossing detection), chip Power supply and output open circuit protection, sometimes the auxiliary winding NAUX can also be used for output short circuit protection detection and input line voltage compensation.
Figure 2 Schematic diagram of a typical primary-side feedback flyback isolated LED driver 
The principle of the flyback isolation LED driver power supply to achieve constant current is:
Is = N * ip (1)
iLED =∫(TOFF/T) *isdt=∫(TOFF/T) * N * ipdt (2)
Where: is the secondary side peak current ip is the primary side peak current TOFF is the demagnetization time T is the demagnetization time N high frequency transformer turns ratio
From equation (2), in order to make the LED output current constant, it is necessary to control the ∫ (TOFF/T) * N * ipdt to be constant by the driving chip. For the chip BP3102, TOFF/T is set to a constant of 0.5, and ip is set by the chip reference voltage.
Ip = 500mV/RCS (3)
This makes it easy to implement an output constant current design iLED = ip/4 * N (4)
Unfinished
For more information, please refer to the September issue of "High-tech LED-Technology and Applications" 
