PoE Flyback Transformer Selection

[veryevil]

Hi, I'm new to flyback power supplies and I'm currently designing one for 22-57Vin and 24Vout @ 0.5A or 1A.

I'm looking at using Linear Techs ideal diode bridge IC LT4321 (Click Here) and their PoE PD IC LT4276 (Click Here).

My plan is for it to be Class 0 or Class 1 with size being the constraint, mainly the transformer.

I have found the following transformer and want to check a couple of things: Wurth 7491195224 (Click Here)

The winding ratio listed on the datasheet 6:9:9:4 is that N1:N2:N3:N4 meaning primary N1 to secondary N2 is 6:9 Secondary N2 to N3 is 9:9 and Secondary N3 to Auxiliary N4 is 9:4?

Also does this provide 2 independent 24V @ 0.5A feeds or is that assuming N2 and N3 are connected in parallel? If not will this transformer give me 24V @ 1A if connected in parallel?

It does seem small to be able to handle 24W which is what makes me question it.

Cheers

[veryevil]

One and only Bump.

[Jay_Diddy_B]

Hi, I'm new to flyback power supplies and I'm currently designing one for 22-57Vin and 24Vout @ 0.5A or 1A.

I'm looking at using Linear Techs ideal diode bridge IC LT4321 (Click Here) and their PoE PD IC LT4276 (Click Here).

My plan is for it to be Class 0 or Class 1 with size being the constraint, mainly the transformer.

I have found the following transformer and want to check a couple of things: Wurth 7491195224 (Click Here)

The winding ratio listed on the datasheet 6:9:9:4 is that N1:N2:N3:N4 meaning primary N1 to secondary N2 is 6:9 Secondary N2 to N3 is 9:9 and Secondary N3 to Auxiliary N4 is 9:4?

Also does this provide 2 independent 24V @ 0.5A feeds or is that assuming N2 and N3 are connected in parallel? If not will this transformer give me 24V @ 1A if connected in parallel?

It does seem small to be able to handle 24W which is what makes me question it.

Cheers

Hi,

The transformer is the correct size. If you look at the 25W demo boards listed here:

http://www.linear.com/product/LT4276#demoboards

And you look up the transformers, you will see that they are a similar size.

The transformer secondary windings should be connected in parallel. This gives the best magnetic coupling between the primary and the secondary.

Page 23 of the LT4276 datasheet shows the schematic that you need.



It use a Wurth 750314782 transformer

Link: http://www.we-online.com/web/en/passive_components_custom_magnetics/products_pbcm/product_spotlight/lt4276.php

Regards,

Jay_Diddy_B