Cirrus-logic AN364 Uživatelský manuál stáhnout pdf (Strana 22)

AN364

22 AN364REV3

Using Equation 13, calculate the transformer T1 secondary RMS current:

Step 11) Determine Output Capacitor

Output capacitor C5 ripple current I

Ripple(RMS)

is the vectorial difference between transformer T1 secondary

current and the DC load current. See Equation 39.

Output capacitor C5 is selected as a 100F, 25V capacitor.

Step 12) Flyback Transformer Specification

Specifications for the flyback transformer T1 can now be compiled to enable suppliers to design within size

and cost constraints.

Step 13) Circuit Adjustments

Now that the transformer has been defined and built, it may need to be adjusted. For more information, see

Circuit Adjustments on page 11.

Step 14) Recalculate R

Sense

Validate that the system meets the operating criteria. This may require adjusting components like R

Sense

and

FBGAIN

. For more information, see Recalculate R

Sense

on page 11.

4.2 Boost Stage Design Steps

Step 15) Determine I

PK(BST)

, I

SAT, and

IPK

(R13)

Using Equation 19, calculate I

PK(BST)

Parameter Value

Output DC Power 6.6W

Converter Topology

CRM flyback

Switching Frequency 85kHz

Primary Inductance

11.3 mH

10%

Peak Primary Current

0.15A

Primary RMS Current 43mA

Turns Ratio N

14.3

Secondary Voltage 15.4V

Secondary RMS Current 0.85A

Primary Leakage Inductance <100H

Primary Voltage

405V

Electrostatic Shield

Between primary and secondary winding

Auxiliary Winding Turns Ratio (N

AUX

)

Auxiliary Wire

Any convenient gauge

Rigidity Sec

Core/Primary/Aux/Shield

>2,500V

RMS

PK FB

N

current

3TT

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

=0.131A14.3

7.45s

312.5s

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

 850mA==

[Eq. 38]

Ripple RMS

0.85A

0.44A

– 0.73A==

[Eq. 39]

PK BST

3.64 P



RMS

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

3.64 7.3W

230V

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

116mA== =

[Eq. 40]

1 2 ... 17 18 19 20 21 22 23 24 25 26 27 28

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