Isolated LED driver scheme based on NCL30000 PF greater than 0.95

For low-power AC-DC LED power conversion, different topologies such as isolated flyback or non-isolated buck can be selected. The so-called "isolation" refers to the electrical isolation between the input and output using a transformer or the like. Both of these topologies have their own characteristics. In comparison, the non-isolated topology design and circuit board configuration are simple, the board size is small, the number of components is small, and the energy efficiency is higher. The isolation topology is easy to meet the safety requirements, but the magnetic design is complicated and requires a large circuit. Board size. This article will focus on the AC-DC LED driver solution in an isolated topology.

LED driver application requirements

For LED general lighting applications, the current cost is relatively high, so high-performance LED drivers will undoubtedly be more popular. In addition, LED drivers should also have high energy efficiency (low loss), high reliability, compliance with electromagnetic interference (EMI) and harmonic content or power factor (PF) standards, flexibility, adapt to wide environmental conditions, and can be retrofitted to existing Application, support for traditional control mode work (compatible with traditional dimming).

Among them, in terms of power factor requirements, the US ENERGY STAR project solid-state lighting standard has mandatory requirements for PFC (regardless of the power level), applicable to specific products, such as recessed lights, cabinet lights and table lamps. Wait. The standard requires a power factor greater than 0.7 for residential applications and a power factor greater than 0.9 for commercial applications, while integral LED bulbs require a lamp power factor greater than 0.7 for input power greater than 5W. Of course, not all countries absolutely mandate improved power factor in lighting applications, but some applications may have this requirement. For example, utilities may strongly promote the commercial use of products with high power factor in utilities.

NCL30000 isolated LED driver solution with high power factor

To provide a high power factor while meeting other application requirements, it is necessary to use a high power factor circuit architecture. As a result, the traditional two-stage architecture (PFC boost + pulse width modulation (PWM) flyback conversion) can not meet the requirements. Advantageously, such as the ON Semiconductor NCL30000 power factor correction dimmable LED driver with a single-segment architecture (see Figure 1), can provide a power factor of 0.9 or higher. The device is packaged in a compact 8-pin surface mount package that uses a critical conduction mode (CrM) flyback architecture to provide a high power factor of greater than 0.95 in a single-segment topology, eliminating the need for dedicated DC-DC conversion power sections. Reduce component count and reduce total system cost.

Figure 1 Comparison of traditional two-stage architecture with improved single-segment architecture

The constant on-time CrM operation of the NCL30000 is especially suitable for isolated flyback LED applications because