Constant-current wall warts streamline LED driver design for lamps, cabinet lights
Margery Conner - May 17, 2012
Consider the lowly wall wart power adapter. It finds use in millions of electronics devices as a cost- and power-efficient ac-dc voltage-regulated power supply. In effect, designers of electronics have outsourced their product’s ac-dc conversion, voltage regulation, and regulatory compliance to the wall wart. It’s a cost-effective solution for most low-wattage power supply challenges.
Here’s a photo of my LED desk lamp. Its designers outsourced some but not all of its power conversion and regulation needs to an ac-dc voltage regulated wall wart. Because LEDs are constant-current rather than constant-voltage devices, the lamp still needs to include current regulation circuitry; virtually all wall warts provide voltage rather than current regulation.
Power supply manufacturer Phihong sees a need here, and has introduced a line of constant current wall-wart adapters that provide the current rather than voltage regulation. Designers of relatively low-power LED applications such as desk lamps or under-cabinet lighting don’t need to worry about driver design or meeting UL or EnergyStar specifications. The PDA006A series consists of 6W LED adapters available in 350mA, 700mA, or 1000mA outputs; The PDA012A series consists of 12W LED adapters available in 350mA, 700mA, 1000mA, or 1500mA outputs; and the final series, designated the PDA024A, consists of 24W LED adapters and is available in 700mA, 1000mA or 1500mA outputs.
All of the drivers feature Level V efficiency markings and have power factors >0.90, and are UL 8750-compliant. Additional standard features for the UL1310 Class 2 output drivers include over-voltage, over-current, short-circuit, and open-circuit protections. The no-load power draw at 115Vac is less than 300mW. Preliminary pricing in single quantities: 6W/12W/24W are $8.66/$13.91/$19.62.