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SMPS PSU (low noise) - questions

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ilya:

--- Quote from: schmitt trigger on May 08, 2019, 07:30:19 pm ---...there are topologies, and modules, which already have both the  +/- output voltages.

--- End quote ---
I took a quick look at the dual output modules that are available from Mouser and most of them have a fixed output voltage with standard values: 15V, 20V, 24V. This menas that I can't feed and LDO with 17V and get a clean 15V after it.
So it seems that it's either two modules or complete custom solution.


--- Quote from: schmitt trigger on May 09, 2019, 04:06:59 pm ---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.

--- End quote ---

Well, this is very promising. No need to sync chips simplifies the task a lot.


--- Quote from: T3sl4co1l on May 09, 2019, 08:32:29 am ---What is the motivation behind independent supplies versus one common supply and load switches?  Do the loads need to be switched at all?

--- End quote ---
The motivation is very simple. Imagine a system that has several different audio modules powered from a single source. The set of modules may differ from system to system. All these modules have different power requirements. One may need just a +24V rail while another needs +/-15V and still another needs +/-30V. Now, I can feed my +/-40V unregulated DC and get +/-30V rails with reasonable power dissipation. Even 24V may be managable. But to get +/-15V working I have to resort to dropping resistors which is not the best solution.

I need to choose the optimal topology for this task. Since I have two rails it may be benefical to use one of them as a positive and another one as a negative. The disadvantage (as I see it) is that I need 2 SMPS chips to do the work. Another solution is to use something like the method described here: http://www.ti.com/lit/an/slva369a/slva369a.pdf
But I doubt I can feed it with 40V and get +/-30V out of it.

Another question is what to do with grounds. With 2 chips solutions it seems pretty straightforward. But with a split-rail system - I can't wrap my head around this. Can I establish the common ground point for all modules in the system?

T3sl4co1l:
Why do the modules take different voltages?  How much load current?

Tim

ilya:

--- Quote from: T3sl4co1l on May 10, 2019, 04:37:11 am ---Why do the modules take different voltages?  How much load current?

--- End quote ---
Different modules have different voltage requirements. This can't be changed.
Load current is in the range of 150-300mA per rail for each module.

T3sl4co1l:
Can you use common e.g. +/-15, 24, 30V supplies, of up to 1.2A each I guess, and each module connects to only the supplies it needs?

I suppose there isn't much savings at that point over four independent supplies, but it's still something.

Why do the modules not have POL regulators internal?  Can they not be changed to do so?

Tim

ilya:
Each module has its own POL regulation. They all take common unregulated +/-40VDC and regulate it down to the needed voltage. Now it's all linear. I want to change this to SMPS for better efficiency and less heat dissipation.

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