Integrated AC/DC converter with no-load over-voltage protection and safe start-up

This paper presents early measurement results of an integrated AC/DC converter, discusses about the start-up problem which was not addressed in our previous work and shows a way to solve it. The AC/DC converter converts the AC voltage of the power grid to regulated 3V DC voltage without need to bulky step-down transformer. Over-voltage problem at light load and no-load conditions due to lack of step-down transformer, is solved by an additional circuitry which prevents the converted voltage from rising high and damaging the converter. To reach less output ripple, a capacitor-less low drop-out (LDO) regulator is cascaded to the output of the converter. The measurements were done for both full-load and half-load of 17mA and 10mA respectively, and it was confirmed that the no-load over-voltage protection scheme works fine. The circuit has been implemented in a 0.35 μm 4M/2P CMOS silicon-on-insulator (SOI) technology with using both 3.3 V and 5V transistors.