Figure 3 Assume ideal components.
-Refer to Figure 3. Assume VIN can vary between +15 V and +18 V. To obtain an output of +12 V, the duty cycle must vary between
A)80% and 90%
B)33% and 67%
C)67% and 80%
D)20% and 33%

Question

Figure 3 Assume ideal components.
-Refer to Figure 3. Assume VIN can vary between +15 V and +18 V. To obtain an output of +12 V, the duty cycle must vary between
A)80% and 90% 
B)33% and 67% 
C)67% and 80% 
D)20% and 33%

Quizplus · Accepted Answer

The output voltage in a buck converter (which is likely the context given the nature of the question) is given by Vout = Vin * Duty Cycle. To maintain a constant output of +12V while Vin varies between +15V and +18V, the duty cycle must adjust accordingly. For Vin = 15V, the duty cycle needed is 12/15 = 0.8 or 80%. For Vin = 18V, the duty cycle needed is 12/18 = 0.67 or 67%. Therefore, the duty cycle must vary between 67% and 80% to maintain a +12V output across the given input voltage range.

Figure 3 Assume Ideal Components