Coupled output inductor in BTL?

[Khron]

Greetings,

I'm planning to make a couple of amps with TAS5630. "On the side", for one reason or another, i've been collecting and scavenging an assortment of old and/or broken computer PSU's, and as such, i've put together quite a stock of toroidal cores. Judging by their color coding, mostly mix -26 and -52 (according to Micrometals color codes).

I'll be running the amps in 2xBTL per each chip. Now, considering that some board-space-saving wouldn't hurt, my question is, is there some way to wind a coupled BTL output inductor, without blowing anything up?

I've got the "mini ring-core calculator" and Micrometals' inductor design/analysis program, to help.

[Pafi]

Hi!

This is a solution (attached).

[81bas]

Originally Posted by Khron

is there some way to wind a coupled BTL output inductor, without blowing anything up?

Also, it is needed to use this chip in AD modulation mode then and feed its inputs with strongly differential signal, as I know...

[81bas]

Originally Posted by Pafi

Hi!

This is a solution (attached).

Very good drawings and explanations!

However I had no success to use coupled inductor in BTL configuration with BD modulation mode earlier... It was working only with AD modulation for me. And the inductor was wound slightly different, than in your drawings. You have shown the 'common mode' inductor (input currents are always in phase), whereas for AD modulation I have used the 'differential mode' inductor (input currents are out of phase).

Please correct, if I am wrong.

[Khron]

Thank you for the speedy replies

As a design factor, i'm guessing the maximum flux in the inductor should be at least twice the flux of a simple / single winding, right?

And does anybody have a clue what modulation the TAS5630 uses?

[81bas]

Originally Posted by Khron

And does anybody have a clue what modulation the TAS5630 uses?

See description of M1,M2,M3 mode selection pins...

[Khron]

Oooooh, yeah Many thanks for the enlightenment

Am i right with my hunch about the core dimensioning, though?

[Pafi]

Originally Posted by 81bas

Very good drawings and explanations!

However I had no success to use coupled inductor in BTL configuration with BD modulation mode earlier... It was working only with AD modulation for me. And the inductor was wound slightly different, than in your drawings. You have shown the 'common mode' inductor (input currents are always in phase), whereas for AD modulation I have used the 'differential mode' inductor (input currents are out of phase).

Please correct, if I am wrong.

Thanx! In BD modulation the magnetizing current have an important role, and to maintain this magnetizing current you need to use a relatively low permeability core for this inductor. Maybe this wasn't low enough in your case. I used it only with BD modulator, and it worked well with 2 stacked AL=60 iron powder core. I think an EE (or RM) core (with huge airgap) would be better, but I haven't try it yet, however I've wound it already.

Input currents are out of phase in my case also, but there is a common mode component too at switching freq. This common mode current would be huge with separated inductors, because of the low switching freq, this is one of the reasons I used this kind of filter. With AD modulation higher fsw is needed, this because the ripple current is not too high.

Khron!

And does anybody have a clue what modulation the TAS5630 uses?

Probably it's BD in bridge mode.

As a design factor, i'm guessing the maximum flux in the inductor should be at least twice the flux of a simple / single winding, right?

You don't have to worry about flux, but it's not that easy. In this inductor the most important thing is the leakage inductance, and this is very hard to calculate, it depends on the winding geometry too. It's better to simply experiment, measure inductance with one end shorted ! Hint: you will need much more turns then usual. In return you will get a much lower core loss.

[Khron]

Pafi, the TAS5630 can work in either AD or BD modulation, in the 2xBTL configuration.

The top sketch in your posted pic resembles how the windings look on common-mode inductors, on SMPS inputs, so i'm guessing the bottom sketch is the differential-mode winding? So that's how a coupled inductor for a bridged amp should be wound? Or... Which type of modulation should be configured, for which type of winding?

And by "one end shorted", i guess you mean with one of the windings shorted, on a "double-wound" toroid, right? (Better safe than sorry )

[Eva]

Note that in the bottom sketch (AD) the flux is always contained within the core, while on the top sketch (BD) the flux becomes progressively spread everywhere (as in a pair of air core inductors) as output voltage becomes higher or lower than 0V.