Datasheet

Output Capacitor Selection
C ³
OUT
= » m147 F
V (V )-
OUT OUT_MIN
2 2
2
P
OUT
h
1
f
LINE
(390V) (240V)-
2 2
2
300W
0.92
1
47Hz
(19)
C =200 Fm
OUT
(20)
2
1 2 300
14
4 0 92 390 4 47 200h p p m
´
´
= = »
´ ´ ´ ´ ´ ´ ´
OUT
RIPPLE
OUT LINE OUT
P
W
V V
V f C . V Hz F
(21)
I =
COUT_100Hz
= =0.591A
P
OUT
V ´ h Ö
OUT
´ 2
300W
390V 0.92´ ´ Ö2
(22)
I =
COUT_HF
- (I )
COUT_100 Hz
2
P 2
OUT
Ö2
2 ´ ´h V
IN_MIN
4 VÖ
IN_MIN
2
9 Vp
OUT
2
(23)
I =
COUT_HF
- (0.591A)
2
300W 2´ Ö2
2 ´ ´0.92 85V
4 85VÖ ´2
9 390Vp ´
2
» 0.966A
(24)
UCC28061
SLUS837A – JUNE 2008 – REVISED JULY 2009 .............................................................................................................................................................. www.ti.com
The output capacitor (C
OUT
) is selected based on holdup requirements as shown in Equation 19 .
Two 100- µ F capacitors were used in parallel for the output capacitor:
For this size capacitor, the output voltage ripple (V
RIPPLE
) is approximately 11 V, as shown in Equation 21 :
In addition to hold-up requirements, a capacitor must be selected so that it can withstand the low-frequency RMS
current (I
COUT_100 Hz
) and the high-frequency RMS current (I
COUT_HF
); see Equation 22 to Equation 24 .
High-voltage electrolytic capacitors generally have both a low- and a high-frequency RMS current rating on the
product data sheets.
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