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# DC power supply design

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Q1. A 9 V power supply delivers 2 A to a resistive load. The a.c. supply is 230 V, 50 Hz and a bridge rectifier is used in conjunction with a 0. 047 farad reservoir capacitor.
Estimate:
(a) The peak-to-peak ripple voltage.
(b) The transformer secondary voltage if the total forward voltage
drop in the rectifier is 2 V at 2 A.

Q2. An aircraft electrical system operates at 115 volts at 400 hertz. It is to supply an average d.c. voltage of 28 volts and an average current of 20 A at a ripple factor of 0.005.
Determine:
a) The r.m.s. ripple voltage.
b) A suitable value of smoothing capacitor.

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#### Solution Preview

Dear student,

One simple setup of the DC power supply can be built using a transformer, full-wave diode bridge rectifier and a reservoir (smoothing) capacitor. The large output capacitor (C) is discharged through a load (R) with the time constant tau = R*C. If the time constant is very large compared to the period of the AC supply waveform (T), the capacitor voltage decrease can be approximated with a linear function. When this condition is satisfied, the calculations can be simplified. The relation tau >> T holds for the sets of parameter values ...

#### Solution Summary

The solution covers a set of important calculations regarding the design of a simple DC power supply using a transformer, diode bridge and a smoothing capacitor. Calculation examples emphasize the estimation of ripple voltage parameters and how to determine the suitable smoothing capacitor value.

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