Which statement correctly describes the control of a switching regulator’s output?

• A. The input voltage controls directly the output.
• B. The frequency of the supply determines the output.
• C. The output is purely non-regulated.
• D. The duty cycle of the switching element controls the output.

Answer: (D)

The output of a switching regulator is controlled by the duty cycle of the switching element. By changing how long the switch stays on during each switching cycle, the regulator sets the average voltage delivered to the output. The device uses feedback to compare the actual output to a reference and then adjusts the duty cycle to keep the output at the desired level. In an ideal buck topology, the output voltage is proportional to the input voltage multiplied by the duty cycle, so increasing on-time raises Vout and decreasing it lowers Vout. The input voltage sets the potential range but does not directly determine the regulated output, while switching frequency mainly affects ripple and efficiency, not the DC level. The output is regulated, not purely non-regulated.