NS 公司的LM3450是具有PFC和相位調(diào)光譯碼器的LED驅(qū)動器,PFC在調(diào)整輸出電壓同時保持輸入端有極好的功率因素.相位調(diào)光70:1 PWM譯碼,具有過壓和反饋短路保護,非常適合離線10-100W的LED驅(qū)動,主要用在調(diào)光筒燈,平光燈和室內(nèi)外區(qū)域照明以誠相待及電源PFC.本文介紹了LM3450主要特性, 方框圖, 典型應(yīng)用電路圖和反激電路圖, PFC系統(tǒng)架構(gòu)圖和控制電路圖, 調(diào)光譯碼器電路圖以及LM3450評估板主要指標,完整電路圖和材料清單(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應(yīng)用:
■ Dimmable downlights, troffers, and lowbays
■ Indoor and outdoor area SSL
■ Power supply PFC
圖1.LM3450方框圖
圖2.LM3450典型應(yīng)用電路圖
圖3.LM3450典型反激電路圖
圖4.PFC系統(tǒng)架構(gòu)圖
圖5.LM3450 PFC控制電路圖
圖6.LM3450 調(diào)光譯碼器電路圖
圖7.LM3450 調(diào)光保持路圖
圖8.LM3450初級偏壓電路圖
LM3450評估板
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評估板主要指標:
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
圖9.LM3450評估板外形圖
圖10.簡化LM3450評估板電路圖
圖11.LM3450評估板偏壓電路
圖12.LM3450輸入EMI濾波器電路
圖13.LM3450評估板完整電路圖
230VAC 評估板材料清單(BOM):
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