摘要：  本文介绍了LM3448主要特性，简化方框图，基本的TRIAC调光电路，典型LED驱动器应用电路以及多种设计案例和指标及其所用材料清单，LM3448 A19 Edison改进型评估板电路图和材料清单。

关键字：  调光，  离线LED驱动器，  固态照明

TI(NS)公司的LM3448 是集成了600V的MOSFET的TRIAC相位调光的离线LED驱动器，应用电压范围从85VAC到265VAC，可调整的开关频率，不会出现120Hz的闪烁，能为大功率LED提供恒流，主要用于改进型TRIAC调光，固态照明，工业和商业照明以及住宅照明。本文介绍了LM3448主要特性，简化方框图，基本的TRIAC调光电路，典型LED驱动器应用电路以及多种设计案例和指标及其所用材料清单，LM3448 A19 Edison改进型评估板电路图和材料清单。

LM3448：Phase Dimmable Offline LED Driver with Integrated FET

The LM3448 is an adaptive constant off-time AC/DC buck (step-down) constant current LED regulator designed to be compatible with TRIAC dimmers. The LM3448 provides a constant current for illuminating high power LEDs and includes a phase angle dim decoder. The dim decoder allows wide range LED dimming using standard forward and reverse phase TRIAC dimmers. The integrated high-voltage and low Rdson MOSFET reduces design complexity while improving LED drive`rm factor LED drivers suitable for integrated LED lamps with very low external component count. The LM3448 also provides the flexibility required to implement both isolated and non-isolated solutions based on the Flyback， Buck or Buck-Boost topology using either active or passive power factor correction (Valley- Fill) circuits. Additional features include thermal shutdown， current limit and VCC under-voltage lockout.

LM3448主要特性：

■ Input phase angle dim decoder circuit for LED dimming

■ Integrated， vertical 600V MOSFET with superior avalanche energy capability

■ Application voltage range 85VAC – 265VAC

■ Adjustable switching frequency

■ Adaptive programmable off-time allows for constant ripple current

■ No 120Hz flicker possible

■ Low quiescent current

■ Thermal shutdown

■ Low profile 16-pin Narrow SOIC package

■ Wave solder capable

LM3448应用：

■ Retrofit TRIAC Dimming

■ Solid State Lighting

■ Industrial and Commercial Lighting

■ Residential Lighting

图1。LM3448简化方框图

图2。基本的TRIAC调光电路

图3。LM3448 AC线检测电路

图4。LM3448采用Valley-Fill PFC的典型非隔离降压转换器

图5。LM3448 典型LED驱动器应用电路

图6。LM3448设计案例(1)：带Valley-Fill PFC 的7W， 120VAC非隔离降压LED驱动器

指标：

• AC Input Voltage: 120VAC nominal (85VAC – 135VAC)

• Output Voltage: 21.1VDC

• LED Output Current: 342mA

LM3448设计案例(1)所用材料清单：

图7。LM3448设计案例(2)：6.5W， 120VAC非隔离A19 Edison改进型LED驱动电路

指标：

• AC Input Voltage: 120VAC nominal (85VAC – 135VAC)

• Output Voltage: 35.7VDC

• LED Output Current: 181mA

This TRIAC dimmer compatible design incorporates the following features:

• AC coupled line-injection for improved power factor performance and LED current regulation，

• Standard VCC start-up and bias circuit，

• VCC derived COFF current source.

图8。LM3448设计案例(3)：6W， 120VAC隔离反激型LED驱动电路

指标：

• AC Input Voltage: 120VAC nominal (85VAC – 135VAC)

• Flyback Output Voltage: 27.1VDC

• LED Output Current: 228mA

This TRIAC dimmer compatible design incorporates the following features:

• Direct line-injection for improved power factor performance，

• Standard VCC start-up with auxiliary winding bias circuit for improved system efficiency，

• Zener diode derived COFF current source for improved VCC ripple rejection，

• Additional TRIAC holding current circuit for improved dimmer performance at low conduction angles，

• Output overvoltage protection (OVP).

图9。LM3448设计案例(4)：6W， 230VAC隔离反激型LED驱动电路

指标：

• AC Input Voltage: 230VAC nominal (180VAC – 265VAC)

• Flyback Output Voltage: 27.0VDC

• LED Output Current: 226mA

This TRIAC dimmer compatible design incorporates the following features:

• Direct line-injection for improved power factor performance

• Standard VCC start-up with auxiliary winding bias circuit for improved system efficiency，

• VCC derived COFF current source，

• Additional TRIAC holding current circuit for improved dimmer performance at low conduction angles，

• Output overvoltage protection (OVP).

LM3448 A19 Edison改进型评估板

This demonstration board highlights the performance of a LM3448 non-isolated LED driver solution that can be used to power a single LED string consisting of eight to twelve series connected LEDs from a 85VRMS to 135VRMS， 60 Hz input power supply.

This is a two-layer board using the bottom and top layer for component placement. The demonstration board can be modified to adjust the LED forward current， the number of series connected LEDs that are driven and the switching frequency. The topology used for this evaluation board eliminates the need for passive power factor correction and results in high power factor with minimal component count which results in a size that can fit in a standard A19 Edison socket. This board will also operate correctly and dim smoothly using most standard TRIAC dimmers.

Refer to the LM3448 datasheet for detailed information regarding the LM3448 device. A schematic and layout have also been included along with measured performance characteristics. A bill of materials is also included that describes the parts used on this demonstration board.

图10。LM3448 A19 Edison改进型评估板外形图

LM3448 A19 Edison改进型评估板主要特性：

Drop-in compatibility with TRIAC dimmers

Line injection circuitry enables PFC values greater than 0.90

Adjustable LED current and switching frequency

Flicker free operation

Contents

LM3448 A19 Edison Retrofit Evaluation Board

AN-2127 LM3448 Edison Eval Board Application Note

图11。LM3448 A19 Edison改进型评估板电路图

LM3448 A19 Edison改进型评估板材料清单：