On-chip AC/DC converter with no-load over-voltage protection and output ripple reduction

In this paper, an AC/DC converter which converts AC voltage of the power grid to regulated 3V DC voltage without need to bulky step-down transformer, is presented. Over-voltage problem at low 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. This circuit reaches 92.2% of full-load (20mA) power efficiency and 5.22mW of no-load power dissipation. For gaining less output ripple, a capacitor-less low drop-out (LDO) regulator is cascaded to the output of converter. Using a novel circuit technique on the active diode part of the design helps to alleviate voltage spikes resulting from switching nature of the proposed converter. The regulated converter reaches 89.8% of power efficiency at full-load and 5.61mW of no-load power dissipation. The circuit is implemented in a 0.35-μm 4M/2P CMOS technology with using both 3.3V and 5V transistors.