Power supply question - again (solved)

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metermannd

Joined Oct 25, 2020
195
After going back and doing final touch-ups to two boards I've been monkeying around with their design (including adjustments per comments on my previous threads), I now turn back to the power supply in which I swapped the 5V regulator from a LM309K to a miniature SMPS per a previous thread.

I'm looking at this and am wondering if this is the most efficient / ideal arrangement, with the split secondary. Right now, the only thing served from the bulk 12V supply is one relay on the output board and the source driver for the LEDs on the display board.

I'm thinking of repowering a section on said output board (I haven't really delved into its design yet). Currently it has a 'mains DC' supply, but as it is possible to run that stage from a 12V supply instead, I want to make that change. (that will be a later thread - would like to know what AAC 'guidance' is on this subject as I didn't see it posted anywhere, yet have seen allusions to such a policy) But I digress...

The transformer is a Signal ST-5-20, each secondary puts out 10VAC and 600mA under maximum load (but I doubt the load is that severe). If I want to drive two SMPS units from this transformer, would I be better off making a single 20VAC winding into one bridge rectifier? Or should I think of kicking it up to the next bigger size (ST-6-20 - 1A rated secondaries)?

From the bridge, would I be better off driving the two SMPS units in tandem (in other words, the bulk DC from the bridge / filter cap fed to both the 12V AND the 5V) or in series (driving the 12V regulator from the bulk DC supply and in turn, the 5V from the 12V supply?)
 

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Wolframore

Joined Jan 21, 2019
2,283
I’m confused, you mention buck converters but diagram has linear? Why not design both and calculate the losses and available power involved, without knowing what the demand is, it’s impossible to make a call. The decision is also dependent on the efficiency of the SMPS involved, I like shooting for highest based on conversion and current output. It’s not a simple call, either can work.
 

Thread Starter

metermannd

Joined Oct 25, 2020
195
The 'linear' regulator shown is this SMPS module: CUI V7805-1500

The 12V module I'm considering is the CUI V7812-1000

...and I've never delved into the mathematical aspect of circuit design (in re: losses / max load requirements) beyond calculating LED or voltage-divider resistors. It may be that a lot of the load assumptions that led to the selection of the original design were based on the fully outfitted version of the four main boards, and with the removal / rearrangement of various portions of the original design, I could well be below the original maximums now.
 
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