We report a pulse width modulation (PWM) buck converter that is able to achieve a power conversion efficiency (PCE) of >80% in light loads (80% efficiency for a wide range of load conditions from 45 mu A to 4.1 mA, while generating 1 V output from 2.5-3.3 V supply. The converter occupies 0.375 mm(2) in 0.18 mu m CMOS processes and requires two external components: 1.2 mu F capacitor and 6.8 mu H inductor.