NS 公司的LM3445是 TRIAC调光兼容的自适应离线AC/DC降压恒流控制器，具有LED调光用的TRIAC调光译码电路，输入电压从80VAC到270VAC，控制LED电流大于1A，可调整开关频率.它的无源PFC电路使得电路有更好的效率. LM3445主要用在后配合的TRIAC调光，固态照明，工业和商业照明以及住宅区照明.本文介绍了LM3445的主要特性， 简化方框图， 典型应用电路， 主从配置框图以及带Valley-Fill 电路的主/从配置框图， LM3445设计案例电路图和材料清单， LM3445评估板电路图和材料清单.此外还介绍了LM3445离线TRIAC调光LED驱动器参考设计(120V和230V)与材料清单.

The LM3445 is an adaptive constant off-time AC/DC buck (step-down) constant current controller designed to be compatible with triac dimmers. The LM3445 provides a constant

current for illuminating high power LEDs and includes a triac dim decoder. The dim decoder allows wide range LED dimming using standard triac dimmers. The high frequency capable architecture allows the use of small external passive components. The LM3445 includes a bleeder circuit to ensure proper triac operation by allowing current flow while the line voltage is low to enable proper firing of the triac. A passive PFC circuit ensures good power factor by drawing current directly from the line for most of the cycle， and provides a constant positive voltage to the buck regulator. Additional features include thermal shutdown， current limit and VCC under- voltage lockout.

LM3445主要特性:
■Triac dim decoder circuit for LED dimming
■Application voltage range 80VAC – 270VAC
■Capable of controlling LED currents greater than 1A
■Adjustable switching frequency
■Low quiescent current
■Adaptive programmable off-time allows for constant ripple current
■Thermal shutdown
■No 120Hz flicker
■Low profile 10 pin MSOP Package
■Patent pending drive architecture

LM3445应用:
■Retro Fit Triac Dimming
■Solid State Lighting
■Industrial and Commercial Lighting
■Residential Lighting

图1.LM3445 LED驱动器典型应用电路

图2.LM3445简化方框图

图3.LM3445的主从配置框图

图4.带分开的Valley-Fill 电路的主/从配置框图

图5.带一个Valley-Fill 电路的主/从配置框图

图6.LM3445设计案例电路图

Input = 90VAC to 135VAC， VLED = 7 x HB LED String Application @ 400 mA
材料清单(BOM):

图7.LM3445 评估板电路图

LM3445离线TRIAC调光LED驱动器参考设计：

LM3445 Off-Line TRIAC Dimmer LED Driver Reference Design
This reference design converts 90 VAC to 135 VAC input， and drives seven， or eight series connected LEDs from 300 to 600 mA average current.. The LM3445 switching frequency is set at a nominal 225 kHz. This is a four layer board using the bottom and top layer for component placement. The reference design can be modified to adjust the LED forward current， the number of series connected LEDs and switching frequency.
A secondary schematic for a 230 VAC implementation is also included.

图8.LM3445 EVB 120V 电路图

图9.LM3445 230V 参考电路图

图10.LM3445TRIACEVAL 板外形图(120V)