12V, 5V, 3A dual power supply based on the LM2596

Hello, I'm trying to design a 12V, 5V, 3A dual power supply based on the LM2596 voltage regulator. Now I need about 2A on both the 12V and the 5V rails. This is supposed to power a SATA HDD and a raspberry pi board. I've attached a schematic here and I was hoping you folks could tell me if it would work? Also can I use the 5V rail to power a raspberry pi along with the HDD in parallel? Feel free to dismantle this circuit completely if necessary. The goal is to provide enough power for all devices the right way!

Any help would be really appreciated. Thanks.

The max Vin is 40V which means you better be sure that your 40V input doesn't go higher than 40V for any reason (i.e. including noise, spikes, surges, instability, etc.)

Also, is your 40V input able to supply enough current to supply both outputs at 3A max? Rough calculation:

12 * 3 = 36W
5 * 3 = 15W

36 + 15 = 51W total

51/efficiency = total actual power needed. Say, efficiency is at 80%, then 51/.80 = 63.8W

63.8/40 = 1.6A

So, your 40V supply will need to be able to supply 1.6A worst case [at 80% efficiency].

Also, you schematic says "Unrectified DC 40V" did you mean "Unregulated DC 40V"?

And, how about EMI filtering on the input of the supply? And, I know the datasheet shows, only a 680uF cap on the inputs, but I wonder if they will be able to respond to high frequency transitions (of which there will be plenty from a SATA HDD). Might be good to add smaller capacitance in parallel.

Also, if your Raspberry PI board is going to be used for development, it's probably better to power it with a supply that will limit the current to around 1A so in the event of a short, you're less likely to fry something.

I would use a linear regulator off the 12V output -- a 7805A for instance. But, take into consideration total current demand (between the HDD and the PI)

Yes I realized the input voltage of 40V is a bit excessive. I think a 15V-0-15V toroid transformer down-converting from 220V AC should do fine. And there was an error in stating "unrectified". I'm still a noob with this. Its supposed to be rectified and filtered. I did read about the EMI filtering and I think a 0.1uf ceramic should do good.

Yes it might be a good idea to seperate the two power supplies (for the Raspberry Pi and the HDD). Thanks for the inputs Steve. This was really helpful!