6. 120 Points] Figure 4 demonstrates the output waveforms for a 300 V to 28 V DC

Question

6. 120 Points] Figure 4 demonstrates the output waveforms for a 300 V to 28 V DC-DC converter which has a generous ripple specification of± 0.5 V. This simulation result shows the impact of stepping the output capacitor ESR value across three values, while keeping the capacitance value fixed at 100 uF. 28.5 29. : 100 mD 200 m 300 mD 21 Vout(t) IL(t) Figure 4: Example cenverter waveforms for notional SMPS The top sub-plot shows the simulated converter output with a 100·F eapaciter an three example ESR values. The bottom sub-plet shows the Gilter inductor current waveform Assume that one of the constraints for this design is that all components must come from the pre-qualified standard component database used by your company. The inductor is to be custom wound, but the output capacitor will (of course) be purchased off-the-shelf. A set of suitable capacitor compon ents from the standard inventory list appears in Table 3. Table 3: Qualified Cepacitor Options Parameter Cap "A" | 150pF 75 V 860 mA Not listed] 120 F 25 V 2.5 A 270 F 50 V 1.8 A 50 m2 $2.7359 Capacitance Value 40 V 1.5 A 200 m2 S0.5883 63 V Voltage Rating Ripple Current 0.75 A 250 m $0.2143 ESR 130 m Price Eachk $0.9534 $1.0851

Explanation / Answer

-Given the simulation waveform of DC-DC converter or Chopper circuit output waveforms.
By keeping the constant value of capacitor of 100micro farad and varying the ESR (Equivalent series resistance) of that capacitor, the waveforms are shown in given figure. given the inductor is custom wound and the capacitor to be purchaed off the shelf.
We need to check the specifications of all the capacitors listed above and conclude the type of capacitor which can be use in this process.
CAPACITOR 'A' - NO

150micro farad, 75V , 860mA , $0.9534
Generally , the value of capacitor is 100 micro farad, but thecapacitor A has 150 micro farad which increase the output voltage of the converter ( DC-DC) . Hence the output will be greater than 28V. Moreover the ESR value of the capacitor is not listed. Hence the capacitor A is not suitable for this job.

CAPACITOR 'B' - NO

120 micro farad. 25V, 2.5A , 130m ohms, $ 1.0851
Generally , the value of capacitor is 100 micro farad, but thecapacitor A has 150 micro farad which increase the output voltage of the converter ( DC-DC) . Hence the output will be greater than 28V. The cost of this capacitor is high.Hence the capacitor B is not suitable for this job.
CAPACITOR 'C'- YES

82 micro farad, 40V, 1.5A, 200mohms, $ 0.5883
The capacitor C can be used in this process, as the capacitor value is slightly less than 100 micro farad.
CAPACITOR 'D'- NO
270 micro farad, 50V, 1.8A, 50mohms, $ 2.7359
Capacitor D is not suitable because it has less ESR value and high capacitance value, cost is too high which is not reommended
CAPACITOR 'E'- YES
Capacitor E can be used in this process asthe ESR value is matching exactly, ripple current is very less and cost is very low.

Recommened capacitor configuration
capacitane value - (40 micro farad- 120 micro farad.)
ESR value of the capacitor - ( 100 milli ohms to 300 milli ohms)
ripple current range - (0.5 A- 2 A)
Voltage rating -( 50-100v)
Price should be less than $1

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