Question 3.31: Design a full-wave rectifier to deliver an average power of ......

We begin with the required input swing. Since the output voltage is approximately equal to V_{p}-2V_{D,on}, we have

V_{i n,p}=3.6\,\mathrm{V}+2V_{D.o n}          (3.95)

≈ 5.2 V.               (3.96)

Thus, the transformer preceding the rectifier must step the line voltage (110 V_{rms} or 220 V_{rms}) down to a peak value of 5.2 V.

Next, we determine the minimum value of the smoothing capacitor that ensures V_{R} ≤ 0.2 V. Rewriting Eq. (3.83) for a full-wave rectifier gives

V_{R}={\frac{I_{L}}{C_{1}\,f_{i n}}}.      (3.83)

V_{R}={\frac{I_{L}}{2C_{1}\,f_{i n}}}       (3.97)

=\frac{2\,\mathrm{W}}{3.6\,\mathrm{V}}\cdot\frac{1}{2C_{1}\,f_{i n}}.       (3.98)

For V_{R} = 0.2 V and f_{in} = 60 Hz,

C_{1}=23.000\,\mu\mathrm{F}.       (3.99)

The diodes must withstand a reverse bias voltage of 5.2 V.