ON Semiconductor Fairchild PFC SPM, Руководство по конструкции

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PFC SPM
®
Design Guide
© 2005 Rev. 1.0.1-2012 Fairchild Semiconductor – System Engineering Group
12
V
FF
:
] [ 4 . 1 V V
FF

(when, input voltage V
AC
= 90[V
AC
])
R
FF
= 33[k Ω ], C
FF
= 100[uF]
Over Current Protection
O C P
O U T
R
19
-
+
PFCM
VAC-
UCC3818
PKLIMIT
VREF(7.5V)
R
40
R
18
R
37
R
38
Fig.8 Over current protection circuit
The actual protection level can be slightly different from the calculated value. It depends on PCB
layout pattern. About demo board, the designed values are:
R
18
= R
40
= 1.2[k Ω ], R
19
= R
37
= 82[k Ω ], R
38
= 1.5[k Ω ]
And the expected OC levels are:
1) OCP level 1
 






     
 
 

40 19 18
37
38
40 18
19 40 19 18
19 40 18
37
38
) (
R R R
R
R
R R
R R
V
I
R R R
R I R V R R
V
R
R
SH
REF
PK
PK SH REF
REF
] [ 40 A I
PK
 
2) OCP level 2
 
40 19
18
18
40 19
R R R
V R
I
I R
V
R
R R
SH
REF
PK
PK SH
REF

  

] [ 50 A I
PK
 