An engineer designs a power supply that consists of a transformer, a full-wave,
ID: 2081800 • Letter: A
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