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Unformatted text preview: KI: EE362L, Fall 09, Test 1. Two Problems. Name: Spa/Wis ﬂﬂ ,, Y,
Show all work on these pages. One sheet of notes permitted. Do not unstaple. m Problem 1. A 120V ‘ 0Hz wall outlet voltage powers a lossless DBR, which in turn :1 / W supplies power to a laptop computer. The computer draws a constant 25W. Suppose that there
is a sudden outage of AC voltage. The DBR capacitor continues to supply 25W to the computer,
but when capacitor voltage Vdc falls to W, the computer shuts off. Thailapsed time is
known as ridethrough capability. / 00 Assuming negligible voltage ripple on the capacitor, how many uF are needed to provide 15 ————.., seconds of ridethrough capability? ,
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J2 C(mG "'” VMW) : Gaga" i7 EE362L, Fall 09, Test 1. Two Problems. Name: K E Y
Show all work on these pages. One sheet of notes permitted. Do not unstaple. Prbblem 1. A 120Vrms2 6QHZ wall outlet voltage powers a lossless DBR, which in turn
supplies power to a laptop computer. The computer draws a constant 35W. Suppose that there
is a sudden outage of AC voltage. The DBR capacitor continues to supply 35W to the computer,
but when capacitor voltage Vdc falls to 100V, the computer shuts off. The elapsed time is known as ridethrough capability. Assuming negligible voltage ripple on the capacitor, how many uF are needed to provide 15
seconds of ridethrough capability? ‘ Z , z. m mam ~
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Show all work on these pages. One sheet of notes permitted. Do not unstaple. Problem 1. A 120Vrms,‘60Hz wall outlet voltage powers a lossless DBR, which in turn
supplies power to a laptopicomputer. The computer draws a constant 35W. Suppose that there
is a sudden outage of AC voltage. The DBR capacitor continues to supply 35W to the computer,
but when capacitor voltage Vdc falls to 80V, the computer shuts off. The elapsed time is known
as ridethrough capability. WW Assuming negligible voltage ripple on the capacitor, how many uF are needed to provide 15
seconds of ridethrough capability? " KEY Problem 2. A common mistake is to assume that the negative terminal of the DC bus of a
rectifier is at zero potential with respect to the building neutral. Consider a rectiﬁer operated
directly from a 120Vrms, 60Hz wall outlet. The load is resistive, and there is no DC capacitor. Analyze the rectiﬁer circuit and determine the voltage waveform of point b with respect to point
n. Explain your reasoning very clearly, and neatly sketch the Vbn waveform. { A . game. ,,
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Vbn) 3'” VW 3 v6 EE362L, Fall 09, Test 2, Oct. 14, 2009. Name: 2 One sheet of notes permitted. To receive full credit, you must show your work. . 50w m 'zsfA” 5 0w a.
1in : 48V J 1L Iout 51— I 2v Hvé’ ’* r23 "4' Buck Converter 0.010
7': lQusee 40%? 2%”9 02W 75”“ A b nverter is operating in steadystate and converts 48Vdc to 12Vdc. The switching frequency
is OOkH , and the load is 60W. L = IOuH, and C = lOOOuF. Assume that Vout has very low ripple. With regard to your graphs: Assume tlmlheMQSFEZFwswit Wﬁﬂ"*'*¥omwndgax§§wf , so les should 9th include zero (,1. ogﬂﬂ L _‘L, _; Z...) 2, ;: V "LE, ;, ’ 550/4920?» L 5g: /2 «g W V ) / cw 6 z" i
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or (3,13%é2rl , ow1ng values for min and max currents and the t1mes at b. Sketch the diode current and use your sketch to determine its peak value. The reason for this
( question is that diodes are rated in peak amperes. 0. Assuming that Vout is constant, sketch the capacitor current and use your sketch to determine its
(w peaktopeak magnitude. The reason for this question is that capacitors are often rated in peakto
: peak amperes. , (1. Use the graph from Part c. to graphically compute the peak—topeak ripple voltage on the capacitor
( and express it in percent of Vout. The reason for this question is that it is desirable for the load
voltage ripple to be less than 1%. ' W all“ W5 40% “my...
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(40‘) W 4mg 1. If you are operating with a Vcont connected to the LEFT input and ma = 1”, what w 11 happen
if you simultaneously connect Vcont to the RIGHT input? (LFIQ) becomé; Zvcoy+. 5‘0 744“ gum/0.5 +0 2’0,
C/UF @ﬂﬂ5 Mi? hem/<7 éﬂwtuﬂ/thﬂ. 2. If a Vcont input signal is peaking at 1.5V, what gain multiplier do you need to hold ma as
close to 1 as possible without exceeding 1? Regarding the PWM Control Circuit: ’\ “WVMink come. ea (55 ML 4% $0 34W
boast" Wham/ac! Is .3}; :1. $35 ;@ 3. Why do we need two comparators instead of just one?
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’ Vac/Vi“ +0 VTTQL 4. If 1.5nanoF results in a 120kHz triangle wave, how many nanoF will give you approximately
a 10kHz triangle wave? J,. F; C; V
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I ’5‘ C C, ) 62 [email protected]«{/Q(/D 5. The output has VA and VB signals. If you View VA with respect to the PC board reference,
with ma = 0, explain what you will see. Show the min/max values. 71MB W49 It" ch eckomt 9151;?! Z41 * D p0! $.40
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2:26 8.55.0 .5202: 23m .moEoboo—m— $39M “Haemmm EE362L, Test 3, Nov. 18, 2009. Name: 2 Regarding the HBridge Circuit: 6. Explain why we need the 1500microF input capacitor.
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load. The. \/ a, gap/Igwmng have, 7100 Muoli kegz’sfmm. 7. WEE tigpefpg': oggﬁiso lﬁgffcaézififz’thﬁtfoﬁ $263912.
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capacitor has 100V, and the parasitic inductance of the current path is 1microH, how long will it
take for the A+ and A MOSFET current to reach 30A burnout? 0’»? dj V. _,, MO...
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W‘ 1’; AAXSM... eeﬁcixee 30A )‘A/ 9. and 10. The series output ﬁlter consists of 100 microH and a net 0.2 microF. If the H—bridge
is producing 120Vac of 60Hz, and SOVac of 250kHz, how many amperes of 60Hz and 24th ZSDK'H‘Z
current are ﬂowing through the ﬁlter capacitors? \COV (o o I+1~ \ I 250 KH? z ‘1 0' 93 in” gan—(zww’Y/o‘t) :élSVJL
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HBridge Inverter
Prof. Mack Grady
Nov. 2, 2009 Fewer fram 12v
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 Fall '11
 GRADY
 Rectifier, Switchedmode power supply, laptop computer, capacitor voltage Vdc, negligible voltage ripple

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