Capacitively Divided an On-Chip AC/DC Converter With No-Load Over-Voltage Protection

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 stepdown transformer, is solved by an additional circuitry which prevents the converted voltage from rising high and damaging the converter. This circuit reaches 92.6% 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 kelvin connection along with applying internal offset to active diode’s comparator, alleviate high frequency ripples resulting from switching nature of the proposed converter. The regulated converter reaches 83.5% of power efficiency at full-load and 5.44mW of no-load power dissipation. The circuit is implemented in a 0.35-micrometer 4M/2P CMOS technology with using both 3.3V and 5V transistors.