LM5025A: LM5025A transformer Calculation

Ting YI

Prodigy 140 points

Part Number: LM5025A

Tool/software:

Hi,

The calculation method provided in the article cannot be accessed. Do you have an alternative calculation method?

e2e.ti.com/.../lm5025a-lm5025a-transformer-calculation

9 months ago

+1 Hong Huang 9 months ago

TI__Guru 64115 points

Hi,

Power Topologies Handbook (ti.com)

Use this link to access.

0 Ting YI 8 months ago in reply to Hong Huang

Prodigy 140 points

Hi,

Additionally, I would like to know how the output inductor of the LM5025AEVB is designed, as the documentation does not explain how to calculate the turns ratio.

0 Hong Huang 8 months ago in reply to Ting YI

TI__Guru 64115 points

Hi,

For output inductor, its inductance design can be seen on n this application note.

https://www.ti.com/lit/an/slua535a/slua535a.pdf?ts=1720257390204

But if you want to design an inductor that is completely different from design an inductor value. You can search the internet to find how to design an inductor after you know the inductor specs based on the above application note.

0 Ting YI 8 months ago in reply to Hong Huang

Prodigy 140 points

HI,

After reviewing the documentation, I noticed that section 4.1.1 only mentions the inductance value but does not mention the calculation of the turns ratio.

I would like to know why the output inductor turns ratio used in the LM5025AEVAL is 4:13.

Thank you for your reply.

+1 Hong Huang 8 months ago in reply to Ting YI

TI__Guru 64115 points

Hi,

B0358 specs show pri:sec = (1-2):(3:4) = 13:4 = 3.25:1, this is to help make auxiliary bias power to LM5025A VCC.

When L2 current is in freewheeling, L2 (4 to 3) is connected to Vout = 3.3V which making L2 (2 to 1) is 3.3V x 3.25 = 10.7V, which is required between 8V and 15V for VCC based on the datasheet recommendation.

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LM5025A: LM5025A transformer Calculation