原标题：NS LM3450带PFC和相位调光译码器的LED驱动方案

　　NS 公司的LM3450是具有PFC和相位调光译码器的LED驱动器,PFC 在调整输出电压同时保持输入端有极好的功率因素.相位调光70:1 PWM译码,具有过压和反馈短路保护,非常适合离线10-100W的LED驱动,主要用在调光筒灯,平光灯和室内外区域照明以诚相待及电源PFC.本文介绍了LM3450主要特性, 方框图, 典型应用电路图和反激电路图, PFC系统架构图和控制电路图, 调光译码器电路图以及LM3450评估板主要指标,完整电路图和材料清单(BOM).

　　LED Driver with Active Power Factor Correction and Phase Dimming Decoder

　　The LM3450 is a power factor controller (PFC) with separate phase dimming decoder. The PFC regulates an accurate output voltage while maintaining excellent power factor at the input. The phase dimming decoder interprets the phase angle and remaps it to a 500Hz PWM output. This combination of features is ideal for implementing a dimmable off-line LED driver for 10-100W loads.

　　The phase dimming decoder has several unique features. A programmable mapping from input to output increases design flexibility, while a dynamic filter and variable sampling rate provide a fast, smooth response to dimmer movement. A dynamic hold circuit ensures that the phase dimmer angle is decoded properly while minimizing the extra power losses associated with holding current.

　　LM3450主要特性:

　　■ Critical conduction mode PFC

　　■ Over-voltage protection

　　■ Feedback short circuit protection

　　■ 70:1 PWM decoded from phase dimmer

　　■ Analog dimming

　　■ Programmable dimming range

　　■ Digital angle and dimmer detection

　　■ Dynamic holding current

　　■ Smooth dimming transitions

　　■ Low power operation

　　■ Start-up pre-regulator bias

　　■ Precision voltage reference

　　LM3450应用:

　　■ Dimmable downlights, troffers, and lowbays

　　■ Indoor and outdoor area SSL

　　■ Power supply PFC

　　图1.LM3450方框图

　　图2.LM3450典型应用电路图

　　图3.LM3450典型反激电路图

　　图4.PFC系统架构图

　　图5.LM3450 PFC控制电路图

　　图6.LM3450 调光译码器电路图

　　图7.LM3450 调光保持路图

　　图8.LM3450初级偏压电路图

　　LM3450评估板

　　The LM3450 evaluation board is designed to provide an AC to LED solution for a 15W LED load. Specifically, it takes an AC mains input and converts it to a constant current output of 350 mA for a series string of 1 to 14 LEDs (maximum LED stack voltage of 45V). There are two assembly versions designed to operate from two different nominal AC input voltages, 120VAC or 230VAC.

　　The board employs a two stage design with an LM3450 flyback primary stage and an LM3409 secondary stage. The LM3450 provides an isolated 50V regulated output voltage and a power factor corrected input current. The LM3409 uses the 50V flyback output as its input and provides a constant current of 350 mA to the LED load. This two stage design provides excellent line and load regulation as well as isolation.

　　The board is comprised of two copper layers with components on both sides and an FR4 dielelctric. The two stage design has several key advantages over a single stage design including:

　　No 120 Hz LED current ripple.

　　Better dimming performance at low dimming levels.

　　Better line disturbance rejection.

　　Better efficiency using small LED stack voltages.

　　LM3450评估板主要指标:

　　Input Voltage Range: VIN = 180VAC to 265VAC

　　Regulated Flyback Output Voltage: VOUT = 50V

　　Maximum LED Stack Voltage: VLED < 45V

　　Regulated LED Current: ILED = 350 mA

　　图9.LM3450评估板外形图

　　图10.简化LM3450评估板电路图

　　图11.LM3450评估板偏压电路

　　图12.LM3450输入EMI滤波器电路

　　图13.LM3450评估板完整电路图

　　230VAC 评估板材料清单(BOM):