Planar Transformer design

[Shadow_warrior]

Hello can I design a 2KVA planar transformer for 10 KHz frequency. I am asking because I didnt find any ferrite material planar cores that can work with this low frequency.

 

[kubeek]

How many kHz? Planar transformers are usually used up to a few tens of watts, getting a single transformer to handle 2KVA will be a major challenge. Also in small volumes planar transformers are likely going to be more expensive than a normal one.

One more thing, when I was designing a roughly 2KVA transformer at IIRC 50kHz, the core size was ETD49 or ETD54. I don´t see how you want to fit that and all the copper windings on a pcb.

 

[Shadow_warrior]

ow many kHz

10KHz

single transformer to handle 2KVA

I guess volume and high losses will be a problem

 

[tomizett]

Seems unlikely. Although planar transformers are generally small, I believe that PKN make some in the killowatt range for their amplifiers.
However, it's my understanding that you're limited to a fairly low number of turns compared to a traditional winding, so they're only viable at higher frequencies. To me, 10kHz seems unusually low for any type of SMPS.

 

[ronsimpson]

My last planar ran at 300khz (forward) and that is why the transformer is small.

 

[tomizett]

Out of curiousity, Ron, may I ask what sort of power it was, roughly how many turns and how many PCB layers you used to achieve it?

 

[ronsimpson]

may I ask

My memory is short and I do not have CAD on this computer. 50 to 75 watts.

I used 4 layers for the power supply with two small break off boards. One break off board goes above the main board and one below.
That is 4layers + 4layers + 4layers.

this is not my design! But much like this.
More in the next post.

 

[ronsimpson]

More:
The transformer in #7 has too much copper loss.
Then I realized the core has a very large surface area so the core loss will transfer to air.
The copper loss does not get out well so I change the transformer.
Here we are only getting one turn per layer. Note I brought out the copper, out side the core, to cool off the copper.

With "normal" transformers I try to have 1/2 the loss in copper and 1/2 in core loss.
In planar transformers the copper does not see much air and the core has great surface area.
I don't remember exactly but I think I had 1/4=copper and 3/4=core loss.

 

[tomizett]

Thanks Ron. I'd not thought about different cooling efficiencies between this and conventional transformers - lots to take into account!
Also, I'd never have thought about stacking different sections pf PCB to up the number of layers. Presumably you've got to reflow solder them together just like massive surface-mount packages.

 

[ronsimpson]

solder them together

I used heavy wire like pins in a connector to connect all three PCBs together.