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SMPS PSU (low noise) - questions
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ilya:
I'm quite new to the SMPS design and I'm looking for help in the following qestions.
The goal is low noise power for sensitive audio equipment. By low noise I mean at least as good as a typical linear PSU with good filtering. I was looking at the reference TI design (http://www.ti.com/tool/pmp5863) which is basically SMPS with LDO post-regulation. I think this is a way to go in my case as well. Here're the details:

* The input to the SMPS is 40VDC (mains transformer into diode bridge and filter caps)
* There are two independent 40VDC rails that can drive two channels
* There are up to 4 different devices that will be powered from the PSU. Each of them will have its own SMPS and LDO sections
* Output voltages depend on the device that is being powered. I estimate the range of +/-15V to +/-30V, up to 300mA on each railNow, here are the questions that I'm stuck with:

* A single device that requires +/-30V should probably have two SMPS step-down sections that are fed from separate rails. Do I need to sync SMPS chips?
* Since there are several devices, do I need to sync SMPS chips between different devices?
* What SMPS chips are better suited for this task? Where do I start from?I appreciate all the help I can get from people with more experience in the field than I have. Thanks!
schmitt trigger:
If I understand your requirements: You will have a pair of main DC busses, unregulated, which will feed several POL regulators.
Is this correct?

Another question: Do you want to design the individual SMPS regulators yourself, or would you consider purchasing ready-made modules?

From these questions, we can start providing with correct feedback.

But I can start with something...there are topologies, and modules, which already have both the  +/- output voltages.
ilya:

--- Quote from: schmitt trigger on May 08, 2019, 07:30:19 pm ---If I understand your requirements: You will have a pair of main DC busses, unregulated, which will feed several POL regulators.
Is this correct?

--- End quote ---

Yes, this is correct


--- Quote from: schmitt trigger on May 08, 2019, 07:30:19 pm ---Do you want to design the individual SMPS regulators yourself, or would you consider purchasing ready-made modules?

--- End quote ---

Ideally I'd like to design the regulators myself. I've browsed through different modules and couldn't find anything suitable. Most of them can't be synced and I have no idea how they will behave together (8 of SMPS modules in a single enclosure, worst case). Besides, most cheap modules are noisy, and decent ones are just too expensive. Another consideration is - I'm planning to enclose the SMPS section in the screen. This is not so easy with modules - they are often too bulky. However, if you think that there are some modules that are worth considering, I'm all ears.

I forgot to mention that I don't need isolation.
T3sl4co1l:
What is the motivation behind independent supplies versus one common supply and load switches?  Do the loads need to be switched at all?

Tim
schmitt trigger:
Understand now.

The only time I've had to synchronize regulators was for a project with a class-D amp power supply. I used the LM2588 boost regulator.

The reason for synchronizing them was that I had intermodulation issues between the supply frequency and the amp frequency.
 
Looking back I realize that I could have had solved the problem another way, that the intermodulation was really caused by less than optimal board layout and/or incorrect filtering.
But at the time, I didn't know any better, and besides synchronization appeared like a novelty which I wanted to try out.
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