DER-186: 350mA @ 12V Max, 85 ~ 265VAC in

This engineering report describes the design for a non-isolated, universal input, 12 V, 350 mA constant voltage/constant current (CV/CC) power supply for LED driver applications, utilizing a LNK605DG device from the LinkSwitch-II family in a tapped inductor buck configuration.

A tapped buck topology is ideal for converters with a high ratio of voltage input to voltage output. This topology provides current multiplication on the output, making it possible to use smaller devices, or to lower dissipation losses in the MOSFET.

The tapped buck, non-isolated topology used in this design lends itself to advantages such as smaller PCB size, a smaller transformer, and greater efficiency than in the flyback topologies described in DER-184 and DER-185 (also using LinkSwitch-II devices.) The worst-case full load efficiency for this design is 80%, which is an improvement over the 74% efficiency of the previous two DER solutions. The EMI filtering is simpler in this buck topology, since there is far less common-mode noise, and lends itself to using fewer components. This design operates primarily in CC mode; CV mode only occurs when the load is disconnected, allowing the supply to operate in a safe mode, indefinitely, with the LED load disconnected.

This document contains the power supply design’s specifications, schematic, bill of materials, inductor specifications, and typical performance characteristics.