SMPS output coupled inductors

[skn96]

Hello All

I'm working on a new power supply design project. This is 2.1 kW , 400 V input (from PFC) and +/-85V output power supply design. I believe that UCC28950 (Phase-Shifted Full-Bridge Controller With Synchronous Rectification) is a good solution.

This power supply drive an audio amplifier and so need to provide two split rails output (please see attached schematic).

I do not have experience with power supply design for audio amplifier and split outputs. I found several full bridge power supply schematics with split rails output and they all had coupled inductors at the output. I rarely have seen these inductors with single output full bridges. I know coupled inductors provide better transient performance but I want to know using them in this application is a must or if it is not a must then what are the trade-off here.

I appreciate your response.

Thanks.

 

[treez]

it is must if you are in current mode control....there is ti.com doc on this , ill dig it out

 

[smijesh]

As an audiophile engineer i would recommend linear power supply for audio amplifier because linear power supply has less conducted and radiated noise than SMPS . SMPS Noise should amplified by audio amplifier and quality of sound should go bad.

If you are not bother about the quality of sound, Then go head with SMPS

You may select Push pull,Half bridge or Full bridge topology with switching frequency above 100Khz

Coupled conductors are not commented for dual power supply , use separate conductors.

We discussed earlier
https://www.edaboard.com/threads/264624/

 

[treez]

3rd page , LHS, point number 5 states coupled inductors are necessary
https://www.ti.com/lit/an/slua119/slua119.pdf

 

[smijesh]

Yes You are right, Coupled instructors are applicable for multiple output and complimentary (± V) output.
We need to take care of winding direction of coupled inductor
For multiple output, same winding direction can use but for complimentary output (± V) the direction of winding will be opposite.
Advantages of coupled inductors are given below
1. It saves space
2. It will improve cross regulation of output
3. Ripple cancellation

 

[FvM]

Confusingly, the schematic symbol in post #1 is showing a common mode choke. That's not the kind of coupled inductor you want in a bipolar dual power supply. The winding direction is however correct for dual positive or dual negative supply.

- - - Updated - - -

I see, smijesh already addresses the point.

 

[Warpspeed]

The problem with audio amplifiers is that at very high power outputs the load can cycle alternately pretty much totally between the rails, and the audio waveforms are often very unsymmetrical and at comparatively low frequencies.

Its difficult to get really good cross regulation when one side is loaded with the whole 2KW for a half cycle, and the other side is unloaded. Cross coupled inductors is a band aid, but every little bit helps.