An engineer designs a power supply that consists of a transformer, a full-wave,

Question

An engineer designs a power supply that consists of a transformer, a full-wave, 4-diode bridge rectifier and a smoothing capacitor. She designed the supply to operate in the U.S. where the power line (mains) frequency and voltage is 60 Hz and 120 V respectively. The ripple voltage at full load is 20 mV. Estimate the ripple voltage when the unmodified supply is used in Qatar where the corresponding values are 50 Hz and 240 V respectively. Assume that the equivalent load resistance stays the same.

Explanation / Answer

Vripple = Iload / f * C

where C - filter capacitor

f - frequency

Iload = Vsupply/ Resistance

for 120V , 60 Hz

Vripple = 20mV.

Vripple = Vs/( f * (Effecct of resistance and capacitor))

20 * 10-3 = 120/ (60 * (Effecct of resistance and capacitor))

(Effecct of resistance and capacitor) = 2/ 20 * 10-3

(Effecct of resistance and capacitor) = 100

for 50 Hz , 240 V supply

Vripple = 240 /50 *(Effecct of resistance and capacitor)

=240/( 50 * 100)

= 48mV

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