Single-winding-inductor, 500V buck LED drivers

August 20, 2015 // By Graham Prophet
Diodes Inc’s AL1678 family of LED drivers are intended for driving non-dimmable retrofit LED bulbs in general illumination applications that do not require high power factor (>0.7).

Ensuring a low total circuit bill-of-material (BOM) cost while keeping performance high, these 500V buck-converter LED drivers support output powers up to 15W for wide-ranging LED lighting applications such as Class-A/B/P and GU10 lamps across all mains line voltages. The AL1678 family, in SO-7 packages, provides a variety of different current-rated 500V MOSFETs that allow designers to select the most appropriate driver to meet the needs of different bulb wattage and cost requirements.

With improved driver topology, the AL1678 family provides circuit flexibility and delivers accurate constant current line and load regulation over the 85 VAC to 277 VAC universal input range. By operating in boundary-conduction mode, the driver keeps EMI low with high efficiency, greater than 90%, which aids with EMC compliance.

The AL1678 LED drivers’ total BOM lamp cost is low because it removes the need for an external high-voltage MOSFET and an auxiliary winding, while requiring only a single external inductor. Integrated protection features include under-voltage lockout, over-temperature protection, LED open- and short-circuit protection, as well as a thermal fold-back function to help improve the system reliability of retrofit LED lamps at high temperature. The AL1678’s SO-7 package also helps improve electrical isolation and offers improved moisture resistance.

Pricing for the different wattage/LED current ratings is; 8W/120 mA - AL1678-08BS7-13 $0.14; 10W/180 mA - AL1678-10BS7-13 $0.15; 15W/240 mA - AL1678-20BS7-13 $0.17 (all 10,000).