DF04M View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
DF04M Datasheet PDF : 42 Pages
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AN1262 APPLICATION NOTE
Figure 12. Secondary feedback: TL431 + optocoupler circuit (I)
VCOMP
3.5
1.5
Not needed
in the L6590A
VFB
L6590
IF
L6590D
L6590A
RB
RH
COMP
CCOMP
RCOMP
=
∆VCOMP
∆IC
IC
1 mA IC
VK
CF
TL431
RF
RL
Vout
Table 16. G1(jω) Implementation: secondary feedback (I)
Symbol
Definition
RL
RL ≈ 0.27 to 2.7 [kΩ]
RH
RH = V-----o---u-2-t--.-–-5----2---.--5-- ⋅ RL
RB
CF
RF
CCOMP
RB < CTRmin ⋅ V-----o-I--Cu---tm--–---a--3-x--.--5--
CF = C-----T-R---R--B---m-⋅---aR---x--H--⋅---⋅R---G--C---1O----0M-----P-
RF = -2----⋅---π-----⋅--1-f--Z----⋅---C-----F- – RH
CCOMP = -2----⋅---π-----⋅---f--P---1--⋅---R----C----O----M----P--
This technique provides very good regulation of the output voltage and galvanic isolation from the primary side
at the same time.
In Table 16 it is possible to find the design relationships useful to derive the part values. Icmax is specified in
the Datasheet (2.5mA).
The following condition should be met:
C-C----T-T---R-R----m-m---a-i-n-x-
≤
G1c
⋅
tan1----8π---0-- ⋅ Φ1c
------------R-----C----O----M----P--------------
⋅
-V----o-I--Cu---tm---–--a--3-x--.--5--
,
(20)
otherwise t will not be possible to find a positive value for RF. If the condition (20) is not met, an optocoupler with
a narrower CTRmin - CTRmax spread should be selected. If that is not possible, either a higher fc or a lower Φm
should be selected and the calculations from step a) to step e) redone.
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