SMPS Related Question and Answer
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[Q-1] Which is the good choice among the 2 options mentioned below to get the 12V as an output? why?
Option I: Input voltage = 48V,Option II: Input voltage = 24V
Answer: We know thatDuty cycle D = Vout / VInput
For case ID = 12/48 = 0.25
For case IID = 12/24 = 0.5
So for case II, the duty cycle is more than case I.It means device is turned ON more time in the second case. while designing SMPS we have to consider the principle mentioned in Q-3.
[Q-2] How to select the inductor for the buck converter?
answer: Once the topology is finalized in the process of power supply design, the next step is selecting the Inductor.We know the following basic equationVoltage across Inductor VL = L di/dtRewriting the above equation as followsL = VL.dt/diVL = Maximum voltage appears across the Inductordt= The time during which the maximum voltage appears across the inductordi = Ripple currentVL The maximum voltage appears across the inductor when the power switch is turned on. During that time the voltage will beVL = VOUT - VINdt = The time during which the maximum voltage appears across the inductor= D/FS= Duty cycle/Switching frequencydi = Ripple current= Generally it is assumed in between 10% to 30% of the load currentBy knowing all these values we can get the required inductor value for the buck converter.
Option I: Input voltage = 48V,Option II: Input voltage = 24V
Answer: We know thatDuty cycle D = Vout / VInput
For case ID = 12/48 = 0.25
For case IID = 12/24 = 0.5
So for case II, the duty cycle is more than case I.It means device is turned ON more time in the second case. while designing SMPS we have to consider the principle mentioned in Q-3.
[Q-2] How to select the inductor for the buck converter?
answer: Once the topology is finalized in the process of power supply design, the next step is selecting the Inductor.We know the following basic equationVoltage across Inductor VL = L di/dtRewriting the above equation as followsL = VL.dt/diVL = Maximum voltage appears across the Inductordt= The time during which the maximum voltage appears across the inductordi = Ripple currentVL The maximum voltage appears across the inductor when the power switch is turned on. During that time the voltage will beVL = VOUT - VINdt = The time during which the maximum voltage appears across the inductor= D/FS= Duty cycle/Switching frequencydi = Ripple current= Generally it is assumed in between 10% to 30% of the load currentBy knowing all these values we can get the required inductor value for the buck converter.
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