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i'd like to build a system in which there will be step down modules that get their power from an ac-dc converter.

there are 5 modules connected to the ac-dc converter (each of them steps down to 5v/5a). 4 of the modules will power a peace of hardware that needs 5v / 3a the 5th module powers an arduino or something like this. i'm planning to input at least 24v (32 would be possible and preferred).

now the question: what power supply do i need? 220v ?a -> 24v or 32v ?a

i've been looking for calculators or discussions on this but it is a bit specific i guess. so if anyone can help me i'd be really thankful!

Thanks in advance!

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2 Answers 2

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I'd go for 220V AC to 24V dc because this type of power supply are likely to be more common and give you more "buy" options. Another reason is this; converting 24V to 5V using a switching regulator will give you more options on the switcher chip because there are fewer switchers capable of converting 32V to 5V than 24V to 5V. Almost without any uncertainty at all, a buck switching regulator that works at 32V will always work at 24V but not vice versa.

Even if you were to choose isolating modules for the final 5V conversion (using a flyback topology to provide isolation) 24V is a standard input voltage.

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  • \$\begingroup\$ Thanks a lot for the information! I can agree with you that the 24v ac-dc converter would fit. What current (output of the converter towards the step down modules) do you suggest? Can i just multiply 5*5a*5v and say 125 -> 24v * 5a? - Thank you for the help so far! \$\endgroup\$
    – blub_v5
    Aug 13, 2015 at 21:28
  • \$\begingroup\$ @blub_v5 you have 4 modules taking 15 watts each and one module maybe taking 1 watt. That's 61 watts in total to be dragged from the 24 V supply but add another 6 watts for module conversion inefficiencies and that takes you to 67 watts - you need an AC/DC converter that is capable of supplying 67 watts while still producing 24 volt on the output. \$\endgroup\$
    – Andy aka
    Aug 14, 2015 at 8:36
  • \$\begingroup\$ Thanks once again! Now i'll have to wait for some time to see if this issue has been solved today! (The power supply was ordered about 1 hour ago.) \$\endgroup\$
    – blub_v5
    Aug 14, 2015 at 10:25
  • \$\begingroup\$ What power supply did you order? \$\endgroup\$
    – Andy aka
    Aug 14, 2015 at 11:32
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What is the input current draw for each of the downstream converters? I would go for a 24V DC supply (minimise the difference between the input and output for the downstream converters) rated at the sum of the maximum input currents for each of the downstream converters + 20% margin.

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