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AN1262 APPLICATION NOTE

Table 18. G1(j

ω) Implementation: secondary feedback (II)

More flexibility is given by the network illustrated in figure 14, applicable with the L6590 and L6590D which have

the error amplifier on board.

,

which is less stringent than (20). The resulting function is:

,

and Table 19 shows how its quantities are defined.

Figure 14. Secondary feedback: TL431 + optocoupler circuit (III)

Symbol

Definition

Select from table 17

R

H

V

out

2.5

–

2.5

------------------------- R

L

⋅

=

R

B

CTR

min

V

out

3.5

–

I

Cmax

-------------------------

K

B

⋅⋅

<

C

F

CTR

max

R

()

⋅

R

B

R

H

G1

0

⋅⋅

-----------------------------------------------------------------

=

R

F

1

2

π f

Z

C

F

⋅⋅

⋅

--------------------------------

R

H

–

=

C

CO M P

1

2

π f

P

R

()

⋅⋅

⋅

---------------------------------------------------------------

=

CTR

max

CTR

min

-----------------------

G1

c

π

180

----------

Φ1

c

⋅





tan

R

F2

-------------------------------------------

1

R

C

R

E

-------

+



–

I

Cmax

-------------------------

⋅⋅

⋅

≤

G1 j

ω

()

V

COMP

∆

V

out

∆

-----------------------

V

CO MP

∆

V

E

∆

-----------------------

V

E

∆

I

C

∆

-----------

⋅

=

I

C

∆

I

F

∆

--------

I

F

∆

V

K

∆

-----------

V

K

∆

V

out

∆

---------------

⋅⋅

⋅

CTR

max

R

E

R

F2

⋅⋅

R

E

R

C

+

() · R

B

R

H

C

F1

⋅⋅

--------------------------------------------------------------------

1

j

ω

-----

1j

ω R

H

R

F1

+

() C

F1

⋅⋅

+

1j

ω R

F2

C

F2

⋅⋅

+

----------------------------------------------------------------

⋅⋅

==

Vout

TL431

L6590

L6590D

Vcc

COMP

VFB