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AN1262 APPLICATION NOTE

Figure 15. Secondary feedback: TL431 + optocoupler circuit (IV)

Table 20. G1(j

ω) Implementation: secondary feedback (IV)

this network can be designed). The bias resistor of the photodiode will be selected so as to sustain the quiescent

old to the neighborhood of the steady state value. During this time the PWM is inhibited by the error amplifier,

1-2 V, to let it work in its active region. In case of constant current regulation, the variation of the output voltage

Symbol

Definition

;

L6590

L6590D

Vcc

VFB

COMP

470 nF

Cs

TL431

Vout

R

L2

15V

V

CC

-----------

k

Ω

[]

>

R

H2

V

CC

2.5

–

2.5

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

R

L2

⋅

=

R

H1

V

out

2.5

–

2.5

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

L1

⋅

=

R

B

CTR

min

V

out

3.5

–

I

Q

2.5

R

L2

----------

+

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

⋅

<

R

C

1

2

π f

Z

C

S

⋅⋅

⋅

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

=

C

F1

CTR

max

R

⋅

F2

R

B

R

H1

G

10

⋅⋅

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

=

R

F1

R

H2

R

C

+

() C

S

⋅

C

F1

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

R

H1

–

=

C

F2

1

2

π R

F2

f

P

⋅⋅

⋅

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

=