Enabling Criteria and Circuits for Low-Power High-Density Off-Grid Converters

This paper presents a hardware efficient realization of a low power grid-tied power supply. The SMPS is enabled through flyback configuration accompanied by simple control circuitry for voltage-dependent constant on-time, which have been designed to maximize power density. It also includes start and power up circuits to enable operation from 85Vac to 120Vac. The design is entirely based on off-the-shelf components and customized magnetic element and results in a well-regulated 3V output voltage from 110Vac, with peak efficiency of 84%, and volume of 1 cm³, The very high power density (3kW/Liter, 50W/cui) is enabled by an optimization process for characterizing the magnetic element, mode of operation and values of key components to facilitate a ratio of I_avg/I_rms close to unity throughout the range of the input voltage. Experimental results validate the optimization method, and verify the operation of the control and power up circuits.