Power stage 12v 5v 3.3v

Projects General Guidance
1

Hi,

I'm building a machine with an arduino uno that controls many i2c multiplexer (mcp23016 and one pca9548ad) and a 0,96" oled. In a recent future, a small audio amplifier will be added (something like 1W)

So far so good... now I have to address the power supply. This project will run on a 12v lead acid battery. For sure, I need a 5v line for the mcp controlled reed relays and an higher voltage to power up the arduino.
Just to not miss anything, I would like to put in a 3,3v line, so that I can connect 3,3v i2c devices (the pca9548 can work at different voltages for each bus).

I was thinking at these three linear regulators:

  • LM2940-12V (low dropout)
  • LM2940-5V
  • LM1117-3.3V

Is there any better solution ?

Thank you,
Robse

2

Is there any better solution ?

Looks decent enough to me, but do you need that first 12V one?

3

  1. Why a 12v regulator? Are you powering some parts off 12v? Are they sensitive to the exact voltage? If they're not, I'd run them directly off the battery. The reason I say this is that if you're running it off a 12v battery, presumably you're running some high-current parts off it, and you don't want to use a linear regulator for high current.

  2. How much current do you need at 5v? If not very much, a 5v LDO regulator is fine. If you're planning to pull more than a few hundred mA from it, you should consider using a buck converter - search eBay for Adjustable Buck Converter. Shouldn't cost you more than a cup of coffee, shipped (order extras if you get one without current limiting, though. The un-current-limited ones, while under a buck each shipped, will die if you accidentally short the output)

  3. If you do a buck converter, put the 3.3v regulator after the stepdown converter. Unless you're pulling serious current at 3.3V, which it doesn't sound like you are, an LDO regulator is fine.

4

DrAzzy:

  1. Why a 12v regulator? Are you powering some parts off 12v?

To be honest, only arduino would be attached there

  1. How much current do you need at 5v? If not very much, a 5v LDO regulator is fine. If you're planning to pull more than a few hundred mA from it, you should consider using a buck converter

I think 500ma max.

For some unknow reason I would prefer linear over switching.

I have to run about 10 8x8 led matrixs too in this project. They are still not in my hands yet, i don't how much they draw.

5

I use a battery only because I want to use it where I don't have a power outlet.

6

To be honest, only arduino would be attached there

Well the input regulator will stand a few more volts than 12. The limit would be set by the working voltage of the input capacitors, they will be about 16V minimum. If it is not sourcing too much current it will be fine.