Extra exam question E7D02

WhyA switchmode voltage regulator works by varying the duty cycle of pulses fed into a filter. A switchmode voltage regulator works by rapidly switching a control element fully on and off and varying the duty cycle of those pulses before smoothing them with an output filter, adjusting that duty cycle to hold the filtered output at the desired voltage, answer B. It doesn't alternate the output between positive and negative voltages, doesn't operate by continuously varying a pass element's conductivity (that's a linear regulator), and doesn't work by switching between two different Zener reference voltages.