LM3450_1 Datasheet, PDF (1/26 Pages) National Semiconductor (TI) – Evaluation Board Maximum LED Stack Voltage

LM3450 Evaluation Board
National Semiconductor
Application Note 2098
James Patterson
November 17, 2010
Introduction
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
350mA for a series string of 1 to 14 LEDs (maximum LED
stack voltage of 45V). There are two assembly versions de-
signed to operate from two different nominal AC input volt-
ages, 120V_AC or 230V_AC.
The board employs a two stage design with an LM3450 fly-
back 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 350mA to the LED load. This two stage design pro-
vides 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 sin-
gle stage design including:
• No 120Hz LED current ripple.
• Better dimming performance at low dimming levels.
• Better line disturbance rejection.
• Better efficiency using small LED stack voltages.
Specifications
120V_AC 15W Version
• Input Voltage Range: V_IN = 90V_AC – 135V_AC
• Regulated Flyback Output Voltage: V_OUT = 50V
• Maximum LED Stack Voltage: V_LED < 45V
• Regulated LED Current: I_LED = 350mA
230V_AC 15W Version
• Input Voltage Range: V_IN = 180V_AC – 265V_AC
• Regulated Flyback Output Voltage: V_OUT = 50V
• Maximum LED Stack Voltage: V_LED < 45V
• Regulated LED Current: I_LED = 350mA
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