Supply rail design

Using Arduino Project Guidance
1

Hi guys

I'm working on a project where I have a distributed supply voltage of 12VDC. My components (µC, sensors,...) need 3.3VDC with a load between 10 and 150mA. I will also connect some addressable LEDs (maximum 6), those need 5VDC and if they are all at full brightness, that can end up to around 360mA. The LEDs will not be powered all the time, only when there is interaction with the unit (probably periods of 1 minute, 4-5 times per hour), so the µC will switch that rail on/off when needed.

There will be 30-40 of these units, and they will be operational 24/7. I'm looking for the most efficient way to create these 3.3VDC and 5VDC supply rails.
What I have looked into are:

  • Buck converters
  • LDOs
  • Capacitor booster

To quantify the most efficient way, I'm taking these factors into account

  • Supply efficiency
  • PCB real estate
  • Price
  • Part count (although that is probably automatically covered by the previous 2)

I already had 4 ideas, but have no experience in selecting these components (when there is actual design criteria), so maybe I don't take everything into account.

  1. 3.3VDC LDO + 5VDC LDO
    Probably the cheapest and easiest solution, but because of the 'high' 12VDC supply voltage, not very efficient.

  2. 3.3VDC Buck + 5VDC LDO
    The buck converter will be on at all time, so give away some PCB real estate for an increase in efficiency. 5VDC is only needed for short amounts of time, so ignore the loss in efficiency.
    Maybe use one of those buck converters with integrated inductor, to decrease the PCB real estate, at an additional cost.

  3. 3.3VDC Buck + 5VDC Buck
    Highest efficiency, but maybe becomes too bulky/pricy

  4. 3.3VDC Buck + 5VDC Capacitor boost
    Seems a bit strange to go down in voltage, and back up again, but maybe a good compromise to get an overal high efficiency? The 3.3VDC converter does need to be specced for a higher power rating, so maybe very inefficient at low loads.

If anybody can chime in on what route to take in this project, that would be great!

Thanks
Tom

2

What about 5V Buck and 3.3V LDO

3

Riva:
What about 5V Buck and 3.3V LDO

I though about that as well. But wouldn't that be less efficient than the second option I proposed, yet identical real estate and price?

Rough estimates:
12V -> 3.3V Buck: 80% efficiency
12V -> 5V LDO: 40% efficiency

12V -> 5V Buck: 80% efficiency
5V -> 3.3V LDO: 65% efficiency
12V -> 5V Buck -> 3.3V LDO: 50% efficiency

I think the 3.3VDC Buck + 5VDC LDO combination is probably the best compromise, but I'm a bit worried about the heat generated by the LDO.

4

5V buck and 3.3V linear regulator (not necessarily LDO but usually they are) is my standard configuration for 3-voltage circuits.

12V, Schottky diode, Pi filter with 1-2 mF bulk capacitance, buck converter (5V supply), linear regulator (3v3 supply). Rock solid.