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Question 1

Answer

fs 10 kHz 10 10 10 10 10 10

L 1 mH 1 1 1 1 1 1

C 10 uF 10 10 10 10 10 10

Vin 30 V 30 30 30 30 30 30

D 0.5 0.1 0.2 0.3 0.4 0.5 0.6

Ripple Delta iL 1.5 A 2.7 2.4 2.1 1.8 1.5 1.2

Vo 15 V 3 6 9 12 15 18

Ripple Delta Vo 0.9375 V 0.3375 0.6 0.7875 0.9 0.9375 0.9

D 0.1 0.2 0.3 0.4 0.5 0.6

A Buck converter is driven by a constant input voltage 30V. The switching frequency is 10kHz, the L and C

of the converter are 1mH and 10F. Calculate the output ripple voltage when duty ratio of the transistor is

0.5.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1

RippleVoltage

Duty Ratio

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10 10 10

1 1 1

10 10 10

30 30 30

0.7 0.8 0.9

0.9 0.6 0.3

21 24 27

0.7875 0.6 0.3375

0.7 0.8 0.9

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Question 2

Answer:

Boundary for discontinuous mode is K < (1-D) and K = 2L/RT and R=2Lfs/K

Vs 48 VVo 10 V

L 0.5 mH

C 10 uF

fs 20 kHz

Assume at the boundary:

D 0.208333

1-D 0.791667

R 25.26316 Ohm

Therefore R > 25.26316 will have discontinuous mode

The parameters of a Buck converter are:

Vs=48V, Vo=10V, L=0.5mH, C=10F, fs=20kHz

Calculate the load resistor R for discontinuous mode operation.

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Question 4

Answer

For continuous mdoe, K>=(1-D)^2D

L 10 uH

Vin 30 V

Vo 60 V

fs 100 kHz

Vo/Vin =M= 1/(1-D)

D=1-1/M 0.5

K= 0.125

R=2L/(KT) 16 Ohm

Io_min 3.75 A

A Boost converter has an L=10H, input voltage = 30V, output voltage = 60V and switching frequency

fs = 100kHz. Calculate the value for minimum load current such that the converter is always operated

in continuous inductor conduction mode for all conditions..

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Question 7

Answer

For Discontinuous mode K < (1-D)^2

Vin 48 V

Vo 24 V

fs 100 kHz

L 10 uH

M 0.5

(i) At boundary Vo/Vin=D/(1-D)

D=M/(1+M) 0.333333333

(1-D)^2 0.444444444

R=2L/(KT) 4.5 OhmThe load resistance should increased 4.5 Ohm

A Buck/Boost converter is operated in the following condition/parameter:

Vin=48V, Vo=24V, fs=100kHz, L=10H, C is large

(i) How much is the load resistance dropped to for discontinuous inductor conduction mode to hap

Derive the expression of the ratio of output voltage ripple when discontinuous mode happens to

current is large Hence calculate the ratio. (iii) Calculate the ratio of the rate of change of output v

ripples for boundary case of discontinuous mode to continuous mode when load current is large.

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en. (ii)

hen load

ltage

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Question8

Answer:

Vin 100 V

fs 50 kHzon time 12 us

Rmin 50 Ohm

Rmax 500 Ohm

Ts=1/fs 0.02 ms

D 0.6

Vo 150 V

Io_max 3

Io_min 0.3

Iin_max 4.5

Iin_min 0.45

Rating _T Vin+Vo 250 V Iin_max 4.5 ARating_D Vin+Vo 250 V Io_max 3 A

Rating_L1 Max(Vin, Vo) 150 V Iin_max 4.5 A

Rating_L2 Max(Vin, Vo) 150 V Io_max 3 A

Rating C1 Vo+Vin 250 V

Rating_C2 Vo 150 V

A Cuk converter is operated at 50kHz switching frequency. The on-state time of the transistor is 12s. The

input voltage is 100V. The load resistance varies between 50-500. Calculate the voltage ratings of all the

circuit components.