DER-398: 550mA @ 9V max, 90 ~ 132VAC in

This document describes a power supply utilizing the LinkSwitch™-PL family (LNK457DG) in a highly compact tapped-buck topology. The topology chosen in this design is a tapped-buck configured to provide low THD, high power factor, and constant current output for the input voltage range of 90 VAC to 132 VAC.

The tapped-buck converter was chosen to overcome the switch duty-cycle and peak current limitation inherent in low voltage designs. It also offers the advantage of reduced current stress on the main switch U1, and reduced voltage stress on the output diode D3. The reduced current stress on the main switch enables the use of a smaller switching device for more cost effective design. The lower voltage stress on the output diode enables the use of low VF (schottky) device for improved efficiency.