This document discusses the sizing of a capacitor for a power supply. It provides calculations to determine the capacitance value needed to maintain voltage regulation within 4% ripple at load currents of 50mA and 150mA, given the power supply specifications of 12V RMS input and 85% of the period where the diode is off. The calculations show capacitance values of 25uF for 50mA load and 50uF for 150mA load would maintain voltage ripple below 1.288V and 1.275V respectively.

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