Design of a single-stage isolated power factor corrected LED driver

Power factor correction is to correct the distorted current into a sinusoidal current and make it in phase with the voltage, so that the power factor is close to 1. Improving the power factor is of great significance for reducing energy consumption, reducing the size and weight of power supply equipment, reducing the cross-sectional area of ​​wires, and reducing the external radiation and conducted interference of power supply equipment. Therefore, LED drivers with power factor correction are becoming more and more popular. This article will take two single-stage isolated power factor correction LED drivers NCP1652A and NCL30001 from ON Semiconductor as examples to introduce the design method and application solution of high-efficiency single-stage power factor correction LED drivers.

The single-stage isolated power factor correction LED driver solutions include: offline high power factor Triac dimmable LED driver based on NCL30000; LED single-stage power factor correction drive solution based on NCP1044 boost converter for high-voltage LED light string; buck-boost flyback conversion LED driver based on NCL1652A controller and constant current LED driver for regional lighting applications based on NCL30001 and NCS1002. This article mainly takes NCP1652A and NCL30001 as examples to introduce the design of single-stage isolated power factor correction LED driver.

Both NCL1652A and NCL30001 work in continuous conduction mode (CCM). This solution integrates PFC and isolated DC-DC conversion circuits and provides constant current to directly drive LEDs. It is equivalent to integrating the two circuits of AC-DC conversion and LED driving, both of which are located in the lighting fixture, eliminating the linear or DC-DC converter integrated in the LED light strip. This integrated solution has fewer power conversion segments, reduces the number of components used (such as optical components, LEDs, electronic components and printed circuit boards, etc.), reduces system costs, and supports higher overall energy efficiency of LED power supplies. Of course, this solution has a higher power density and may not be suitable for all regional lighting applications. Its optical pattern may be more suitable for low-power LEDs. Typical applications include LED street lights, exterior wall lights, wall washers and refrigerator cabinet lighting.

LED drivers for general purpose power supplies, telecom power supplies

The NCP1652A controller is designed specifically for buck-boost flyback converter applications in continuous conduction mode (CCM). It can provide a second gate drive output for active clamp buffering in higher power applications. Voltage spikes caused by leakage inductance energy of the flyback transformer are a significant issue. The NCP1652A can be used to design a relatively novel and simple offline power factor corrected 15 Vdc and higher output power supply using an isolated single-stage conversion topology for general power supplies, telecom distributed power front ends, and constant voltage LED drivers for area lighting and distributed lighting applications. The single-stage power factor corrected LED driver based on the NCP1652A controller, as shown in Figure 1, uses a universal AC input 48V DC, 2A power supply. The flyback transformer T1 only requires relatively few magnetic current components for high-efficiency continuous conduction mode. Test results show that this solution can provide nearly 90% energy efficiency and a power factor of more than 0.95 under most typical loads.

LED Drivers for Area Lighting Applications

The NCL30001 controller also features high-voltage startup circuits, voltage feed-forward to improve loop response, input undervoltage detection, internal overload timer, latch input, and high-precision multiplier to reduce input line harmonics. The NCS1002 is a secondary-side constant voltage constant current (CVCC) controller suitable for regional lighting applications such as LED street lights. With the NCL30001 controller, a high-efficiency, dimming-enabled LED driver demo board can be designed. It can be used for applications requiring direct constant current output in the 40W to 100W power range. The current can be adjusted between 0.7A and 1.5A. With a wider range of high-power, high-brightness LEDs, it is suitable for constant current LED drivers in regional lighting applications such as elevated, tunnels, parking lots, and road lighting. The 90W demo board based on NCL30001 and NCS10002, as shown in Figure 2, shows that the efficiency is higher than 87% at 50W output power, 1000mA output voltage/48V forward voltage drop, and the power factor is higher than 0.9 at 50% to 100% load conditions. This special design is optimized for LEDs that require a drive capability greater than 3A, such as Luminus Devices' CSM360 and SST90. This design can support up to 8 SST90s in series or 2 CSM360 devices. The CSM360 LED has a nominal forward voltage of 12.8 V at a drive current of 3.2A, which can produce 1600-3900 lumens depending on the color temperature and luminous flux.

Summarize:

The use of a single-stage topology can greatly reduce the overall component material cost, while also achieving high power factor and good startup characteristics in a compact structure. In order to ensure the robustness and reliability of the solution, multiple protections are used in the above design solutions.