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## Eval_3k3_psfb

Level 1
Level 1
Hi,
Kindly help in designing custom transformer for same EVK. Provide any sheet to design transformer from scratch.
I have calculated inductance and turn ratio. I am not able to determine how much turns to use in primary or secondary.
Example: Turn Ratio: 5:1
primary turns can be 5 or 10 or 15 any... So in this case how to choose number of turns?

Vikas Dabas
1 Solution

## Re: Eval_3k3_psfb

Moderator
Moderator

Hi,

This book has example case studies for fly back as well as half and full bridge transformer design. It is a step by step guide for transformer and inductor design.
Let me know if this helped you in your transformer design.

Regards,
Abhilash P

5 Replies

Level 1
Level 1
Hi,
Vikas

## Re: Eval_3k3_psfb

Moderator
Moderator
Moved post to the right forum.

## Re: Eval_3k3_psfb

Moderator
Moderator

Hi,

The number of turns on the primary and secondary depends on the following,
1) The turns ratio.
2) The voltage per turn rating of the wire used in the transformer winding.
3) The total copper losses expected.
4) The size of the transformer.
5) The window area.
6) The type of core used ( Flux density dependency)
7) The transformer shouldn’t enter the saturation region. (Ni limit vs AI value)

Please find below the variation of peak flux density with an increase in primary turns,

Regards,
Abhilash P

## Re: Eval_3k3_psfb

Level 1
Level 1
Abhilash P wrote:
Hi,

The number of turns on the primary and secondary depends on the following,
1) The turns ratio.
2) The voltage per turn rating of the wire used in the transformer winding.
3) The total copper losses expected.
4) The size of the transformer.
5) The window area.
6) The type of core used ( Flux density dependency)
7) The transformer shouldn’t enter the saturation region. (Ni limit vs AI value)

Please find below the variation of peak flux density with an increase in primary turns,

https://techweb.rohm.com/knowledge/acdc/acdc_pwm/acdc_pwm05/6734
https://techweb.rohm.com/knowledge/acdc/acdc_pwm/acdc_pwm05/6823

For detailed design of Converter magnetics, please refer to the following link,

https://www.ti.com/seclit/ml/slup132/slup132.pdf

Regards,
Abhilash P

Thanks for reply. But i have gone through this theory multiple times and unable to conclude.
Kindly provide step by step design guide. All points suggested above are known but dont know how they affect number of turns.
If possible, please share example of transformer design. You have multiple design of 3.3KW full bridge. You can take any transformer specs and choose core and number of turns.

Regards

Moderator
Moderator

Hi,