AN2794 datasheet(13/39 Pages) STMICROELECTRONICS

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AN2794

Design considerations

Doc ID 14827 Rev 2

13/39

●

HF transformer design

The design method is based on the Kg core geometry approach. The design can be done

according to the specifications in Table 3.

The first step is to compute the transformer apparent power given by:

Equation 28

The second step is the electrical condition parameter calculation Ke:

Equation 29

where Kf=4 is the waveform coefficient (for square waves).

Equation 30

The next step is to calculate the core geometry parameter:

Equation 31

Table 3.

HF transformer design parameters

Specification

Symbol

Value

Nominal input voltage

Vin

24 V

Maximum input voltage

Vinmax

28 V

Minimum input voltage

Vinmin

20 V

RMS input current

Iin

41.4 A

Nominal output voltage

Vout

350 V

Output current

Iout

2.86 A

Switching frequency

100 kHz

Efficiency

98%

Regulation

0.05%

Max operating flux density

0.05T

Window utilization

0.3

Duty cycle

Dmax

0.45

Temperature rise

30 °C

2021

)

(

()4

145

•

()

5800

)

(

)

000

100

(

)

(

145

348

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