References for Power Supply Design


#1

Hi all,

I was wondering if anyone here has go to references (books, videos, articles, whitepapers, datasheets, etc.) for power supply design, particularly for the hybrid synth/eurorack/mixed signal/low cost applications we hold so near and dear.

In particular I’m wondering:

  • What’s the criteria for whether or not to have separate regulators for analog and digital supplies? Analog current draw from other things? PCB real estate? Transmission line length? All of the above? I notice some of the STM32F4+WM8731 modules have two regulators, some don’t.

  • How does one choose regulator packages? I notice LM1117 has the same current ratings for all packages, but do the larger packages just offer better heat dissipation? That’s really all that jumps out at me in the datasheet, but I’m not sure how one designs for this.

  • For the case of different voltage positive rails, is it best to cascade regulators (like o_C’s +5V and +3V3)? This makes sense to me as it seems like less effort for the 3.3V regulator to regulate down from 5V rather than 12V, but you just have to make sure this doesn’t cause too much current draw through the 5V regulator? (But I guess 800 mA * 5V would be pretty hard to get to in a well designed eurorack module with reasonable hp :slight_smile:) Are there other considerations?

Disclaimer: haven’t watched any of the Lanterman videos. Sorry in advance if any of these questions are hopelessly uninformed!


#2

What’s the criteria for whether or not to have separate regulators for analog and digital supplies?

Does it significantly decrease one of the criteria you care about?

PCB real estate?

That’s certainly a factor.

How does one choose regulator packages?

Ideally, as big as you can for heat dissipation.

is it best to cascade regulators

The reason for the 12V -> 5V -> 3.3V scheme is that you can use a jumper to power the +5V rail by the bus. Or some MCUs or Codecs actually need 5V.

I’m not sure about the heat dissipation argument. Sure, a 3.3V regulator regulating down 12V must dissipate a lot of heat, but not that much more than in the 12V -> 5V case. So if heat dissipation is the main issue, just use a large regulator (not two smaller part sharing the work).

is it best to cascade regulators

Sometimes you’ll see a DC-DC regulator (then not wasting any heat) for 12V to 5V, and then a linear regulator for 5V to 3.3V, in the hope that it gets rid of all the noise generated by the DC-DC regulator. It doesn’t always work that well.