GATE EE 2025 Set 1 — Question 60
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Power Electronics → DC-DC Converters → Buck Converter
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Question
The steady state capacitor current of a conventional DC-DC buck converter, working in CCM, is shown in one switching cycle. If the input voltage is , the value of the inductor used, in mH, is _____________ (round off to one decimal place).
Correct answer
1.7 to 1.9
Solution
In a buck converter, the capacitor current is the ripple component of the inductor current .
The current crosses zero at during the rising ramp. For a symmetric triangular wave centered at zero, the zero crossing occurs at the midpoint of the ramp. Thus, the on-time () is:
Duty cycle .
The value of the inductor is .
1.Determine Inductor Current Ripple ():
From the waveform, the peak-to-peak ripple in inductor current is:2.Determine Duty Cycle () and Switching Period ():
The total period . The current crosses zero at during the rising ramp. For a symmetric triangular wave centered at zero, the zero crossing occurs at the midpoint of the ramp. Thus, the on-time () is:
Duty cycle .
3.Calculate Output Voltage ():
4.Calculate Inductance ():
During the on-time, the voltage across the inductor is :The value of the inductor is .
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