1) A MOSFET transistor is being used as a converter switch in a 100v system. It

Question

1)      A MOSFET transistor is being used as a converter switch in a 100v system. It is switching at 50 KHz and has a linear transition time of 3us. The full load current is 40 amps. -          How much average power is being wasted due to switching? -          If this is the only loss mechanism, what is the system efficiency? -          What transition times would be needed to achieve an efficiency of 90%? _____   40%? ____ -          If the frequency is doubled, describe the change in efficiency? _______________ 1)      A MOSFET transistor is being used as a converter switch in a 100v system. It is switching at 50 KHz and has a linear transition time of 3us. The full load current is 40 amps. -          How much average power is being wasted due to switching? -          If this is the only loss mechanism, what is the system efficiency? -          What transition times would be needed to achieve an efficiency of 90%? _____   40%? ____ -          If the frequency is doubled, describe the change in efficiency? _______________

Explanation / Answer

power =V*I/2 =100*40/2 = 20000

efficiency = (1/3)/(1/3+50 ) = 86

for 90 % ,

0.9 = x/(x+50)

x = 0.9*50/0.1 = 450

transition = 1/450 =2.2*10^-6 s

for 40 % , trasition = 30 *10 ^-6 s

when frequency is double , effieicncy = (1/3)/( 1/3+100) =76.9 %

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