This document discusses the sizing of a capacitor for a power supply circuit. It provides calculations to determine the capacitance value needed to maintain the output voltage ripple below 1.5% for load currents of 50mA and 150mA, given the power supply specifications of 12V rms input voltage and 1.4V maximum output voltage drop. The calculations show a 25uF capacitor is sufficient for the 50mA load and a 47uF capacitor is needed for the 150mA load.

1. power supply
mA
mA
Voltage divider 0.2 mA
650.2 mA
•
IL= 50 mA

2. •
E s(rms) = 12
E s(peak) = 12 x = 16.97 V
E s(p-p) = 2x16.97 = 33.94 V.
• C
Ec(peak) = 16.97 – 1.4 = 15.54
• power supply
diode off ≈ 85% of ripple period
f ripple = 2 fline = 2(50) = 100 Hz
P ripple = = = 10 ms
• T off = pripple x 85% = 10m x 85% = 8.5 ms
• C = = 25 uF
• E c(min) = 15.54 – 1.69 = 13.85 V

3. 25
uF uF
• VRipple = = 1.288 V
• %
IL= 150 mA
•
E s(rms) = 12
E s(peak) = 12 x = 16.97 V
E s(p-p) = 2x16.97 = 33.94 V.
• C
Ec(peak) = 16.97 – 1.4 = 15.54

4. • power supply
diode off ≈ 85% of ripple period
f ripple = 2 fline = 2(50) = 100 Hz
P ripple = = = 10 ms
• T off = pripple x 85% = 10m x 85% = 8.5 ms
• C = = uF
• E c(min) = 15.54 – 1.69 = 13.85 V
• uF
uF
• VRipple = = 1.275 V
• 04 %
C Datasheet output
C