A Cuk converter has an input of 12V and is to have an output of -18V supplying a 40W load at the switching frequency 50 kHz. Select the duty ratio, and the two inductors and C1 such that the range in inductor current is no more than 10% of the average inductor current, and the ripple voltage across C1 is no more than 5%. Solution we know that Vo/Vin = D/D-1 or -18/12 = D/D-1 2/3 = 1-D/-D -2D = 3-3D D = 3 or duty ratio = 3:1.