TI（NS）公司的LM3448 是集成了600V的MOSFET的TRIAC相位調光的離線LED驅動器，應用電壓范圍從85VAC到265VAC，可調整的開關頻率，不會出現120Hz的閃爍，能為大功率LED提供恒流，主要用于改進型TRIAC調光，固態(tài)照明，工業(yè)和商業(yè)照明以及住宅照明。本文介紹了LM3448主要特性，簡化方框圖，基本的TRIAC調光電路，典型LED驅動器應用電路以及多種設計案例和指標及其所用材料清單，LM3448 A19 Edison改進型評估板電路圖和材料清單。
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應用：
■ Retrofit TRIAC Dimming
■ Solid State Lighting
■ Industrial and Commercial Lighting
■ Residential Lighting
圖1。LM3448簡化方框圖
圖2?；镜腡RIAC調光電路
圖3。LM3448 AC線檢測電路
圖4。LM3448采用Valley-Fill PFC的典型非隔離降壓轉換器
圖5。LM3448 典型LED驅動器應用電路
圖6。LM3448設計案例（1）：帶Valley-Fill PFC 的7W, 120VAC非隔離降壓LED驅動器
指標：
• AC Input Voltage: 120VAC nominal (85VAC – 135VAC)
• Output Voltage: 21.1VDC
• LED Output Current: 342mA
LM3448設計案例（1）所用材料清單：
圖7。LM3448設計案例（2）：6.5W, 120VAC非隔離A19 Edison改進型LED驅動電路
指標：
• 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.
圖8。LM3448設計案例（3）：6W, 120VAC隔離反激型LED驅動電路
指標：
• 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).
圖9。LM3448設計案例（4）：6W, 230VAC隔離反激型LED驅動電路
指標：
• 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改進型評估板
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.
圖10。LM3448 A19 Edison改進型評估板外形圖
LM3448 A19 Edison改進型評估板主要特性：
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
圖11。LM3448 A19 Edison改進型評估板電路圖
LM3448 A19 Edison改進型評估板材料清單：
詳情請見：
http://www.national.com/ds/LM/LM3448.pdf
和
http://www.national.com/an/AN/AN-2127.pdf#page=2
