Cirrus-logic AN368 Manual de usuario descargar pdf (Pagina 57)

AN368

AN368REV2 57

The FBAUX pin current must be limited to less than 1mA. Resistor R22 plus R23 should be chosen such that

current V

AUX

/(R22 + R23) should be less than 1mA during the time when FET Q5 is ‘ON’ or ‘OFF’. A series

resistor of at least 22k must be used to limit the current.

k. Determine Output Capacitors

Channel 1 output capacitor C8 ripple current I

Ripple(RMS)

is the vectorial difference between transformer TX1

secondary current and the DC load current. See Equation 113.

Capacitor C8 is selected to be a 16volt, 100F electrolytic capacitor. Channel 2 output capacitor C15 is

calculated using Equation 114:

Capacitor C15 was selected to be a 68F with a16V voltage rating.

l. Flyback Transformer Design

The flyback transformer is specified with a EE13/6/6 core and the effective cross-sectional area A

of the core

is 20.1mm

. The peak flux density B

is equal to 213mT. Calculate the flyback transformer TX1 gap length I

using Equation 34:

The primary turns N

is calculated using Equation 35:

The secondary turns N

is calculated using Equation 36:

Ripple RMS

1.016A

0.488A

– 0.89A==

[Eq. 113]

C15

0.213A 100F

0.488A

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

= 43.65F=

[Eq. 114]

0.5 

PK1 FB



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

=

0.5= 1.26Hm3543H

299mA

213mT

20.1mm



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



0.219mm=

[Eq. 115]

PK1 FB



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

 3543H

299mA

213mT 20.1mm



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

247===

[Eq. 116]

-------

247

5.57

-----------

44== =

[Eq. 117]

1 2 ... 52 53 54 55 56 57 58 59 60 61 62 ... 79 80

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Cirrus-logic AN368 Manual de usuario Pagina 57

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