Cirrus-logic AN364 Manual de usuario descargar pdf (Pagina 9)

AN364

AN364REV3 9

Figure 4 illustrates the switching frequency used in the system design.

Solve for T1 and T2 using Equation 7 and Equation 8:

Period T1 is limited to a maximum duration of 8.8s by the IC algorithm. Verify that period T1 at full power is

less that 7.8s, leaving sufficient time for a probe cycle, which requires a slightly longer T1 period.

Step 6) Calculate Peak Current on the Flyback Primary-side

Calculate I

PK(FB)

using Equation 9:

where

= switching period at full brightness (full load condition)

= period T1 at full brightness (full load condition)

Step 7) Calculate R

Sense

(R23)

Calculate sense resistor R

Sense

(R23) for flyback using Equation 10:

where

R23 = R

Sense

in 

Step 8) Calculate the Flyback Primary-side Inductance

i(t)

T1 T2

No Current

Peak Primary Current, I

PK(FB)

Primary

Current

Secondary

Current

Figure 4. Timing Diagram of T1, T2, T3, and TT

--------- T 3–

Reflected

BST

+

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

=

[Eq. 7]

--------- T 3–

BST

Reflected

BST

+

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

=

[Eq. 8]

PK FB

OUT max

 V

BST

 T1



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

=

[Eq. 9]

Sense

1.4V

PK FB

------------------=

[Eq. 10]

BST

T1

PK FB

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

[Eq. 11]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 27 28

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Cirrus-logic AN364 Manual de usuario Pagina 9

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