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smps intermediate voltage or not?

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kars:
hi all,
For a project im working on an AC/DC SMPS.
Quick specs:

* in: 230V AC 50HZ
* out: 50VDC, ≈1A, 5VDC ≈10A, 3.3VDC ≈0.5A ive been concidering the following options: flyback converter with 3 transformer outputs for the voltages OR a flyback converter outputting an intermediate voltage (50V) and using a buck converter to generate the 5V rail.
I do realize the latter one would lower the efficiency of the supply. the thing is im not shure if there are suitable transformers availible for the first option
Wich of these options would you guys/girls/whatever reccomend? Do you have other suggestions?
Thanks in advance!
Kars

richard.cs:
It depends a lot on the regulation accuracy required and the load variability. Multi-winding flyback converters normally have one well-regulated winding and the others loosely regulated. You could for example design it for a well regulated 5 V output, a loosely regulated 50 V, and then use a small buck converter to generate the 3.3 V from the 5 V.

Another topology to consider, and which gives you all windings fully regulated, is a flyback outputting 50 V and a lower voltage, say 8 V, with the 50 V output being the regulated one. You then use buck converters for the low voltage supplies but only with a low voltage ratio which tends to allow higher efficiency. For the 5 V 10 A supply you will probably also want active rectification.

kars:

--- Quote from: richard.cs on September 18, 2019, 10:05:47 am ---Multi-winding flyback converters normally have one well-regulated winding and the others loosely regulated.

--- End quote ---
Ah, now that suggestion of a piece of software makes sense! it indeed suggested a feedback block on only one of the windings.


--- Quote from: richard.cs on September 18, 2019, 10:05:47 am ---You could for example design it for a well regulated 5 V output, a loosely regulated 50 V

--- End quote ---
i think im gonna go for this solution actually, that 5V winding needs better regulation than the 50V one. perfect!
Thanks!

richard.cs:

--- Quote from: kars on September 18, 2019, 10:25:26 am ---Ah, now that suggestion of a piece of software makes sense! it indeed suggested a feedback block on only one of the windings.

--- End quote ---

You can take feedback from one winding or several (one only is common) but because the controller has only one control axis (total power into the transformer) controlling from multiple windings makes the regulation on all of them somewhat poor rather than one very good one and the others bad. The total error is the same (caused by varying load-related voltage drops in the different windings and rectifiers so they don't stay perfectly ratiometric) you just change how it is distributed. You can also introduce interesting stability problems if you take feedback from several windings or from a single winding which is lightly loaded compared with the others.

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