Designing a power supply

So my next project is a bit more ambitious. Ok a lot more. I want to power it via a wall wart (ie not USB / battery) and run the following items:

3 x micro gear motors: (6-12 VDC, 360ma@6 and 1600ma@12VDC stall current) - likelihood of simultaneous operation: 0.001%
1 x Led light bar (12V @ 30ma)
Max: ~4.8A @ 12VDC

1 x fan: 5V @ 200ma
1 x ATMega328 @ 5V (??? ma)
(Up to) 3 x USB @ 5V (500ma max) - possibly but unlikely simultaneously
Max:~2A @ 5V

various switches and dials, etc.

I was thinking a couple of these: ( for the motor / LED section and use this: as a template for the power supply design, but the 317 has 1.5A max output.

I'd like to put everything into one or two boards, rather than have breakout boards and headers, etc. ie design a board for it.

Can I split the wall wart Vin into a 6-12V supply for the motors as well as a supply to a 5V reg for the 328+USB, etc?

Any suggestions for a 5V regulator that can handle a couple of amps output?

Any suggestions for power supply design?

For larger current outputs with a linear regulator it is usual to use a chip that drives an external
pass transistor to boost the current handling. You will need to consider heat dissipation and heat-sinking.

If you run both supplies from the same raw supply then you'll want to ensure the raw supply won't
overload in the worst case of motor operation (otherwise the other supply rail will be crow-barred
and cause a reset). Very short periods of overload can be mitigated by adding lots of decoupling on
the motor supply (1,000uF to 10,000uF ??).

A computer supply for a small form-factor machine (like a Shuttle) would have 12 and 5 or 3.3V outputs with more
than adequate power handling for your needs - you may be able to find one cheap?

Ooh yes PC power supply is a great idea, thanks.

Eesh so I found one. Big.

After careful balking at the size of that PSU I'm going to design this circuit so only one motor can be turned on at a time.

Huh. How about this:

Looks about right?

Wondering about using a SMPS now. A 5V regulator regulating a 12V supply would be inefficient.

The PS I mentioned above has some bad reviews on the Sparkfun site :frowning:

Small switching supplies (China) are dirt cheap on eBay. They are 80-90% efficient and very adjustable. Even a 10A supply is quite compact. I've had good luck with them. Linear regulation is not used today beyond 1A or so.


I have read so many websites recently my eyes are bleeding. Including 100s of forum threads here.

Thanks for the encouragement!