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Help deciding on voltage regulation

This is probably a very basic question, but it is troubling me.

In my robot's design, I have a couple of daughterboards running PICs (or maybe other uC's). I want to design a circuit for supplying power to the daugherboards.

The main power source is a battery pack that supplies 12V. What I'm trying to decide is whether I design one extra daughterboard for voltage regulation or if I include voltage regulation in each one of the daughterboards. Here's what I see as advantages and disadvantes of each method, please critique.

One VReg ======== Advantages:

- savings in real estate

- savings in power consumption Disadvantages:

- If I install a diode or a bridge rectifier on the daughterboard, I won't have 5V for the electronics because of the v.drop of the diodes

- If one of the daughterboards needs 3.3V instead of 5V, I will need a vreg on the daughterboard anyway

Distributed VRegs ================= Advantages:

- Each board is encapsulated, which means I can connect any voltage (in between vreg specified min and max) that it will work

- I can select a specific vreg for each board according to its characteristics (current and voltage needs)

- I may choose a vreg with overvoltage and overcurrent features

- I can implement the reverse polarity diode before the vreg, therefore the diode voltage drop won't affect the voltage available for the load Disadvantages

- real estate

- power consumption

(cost is not really a problem... this is not going to production)

Cheers

Padu

Reply to
Padu
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I generally do it both ways. I have a small switcher daughterboard that provides

5v via a switching reg, which covers most stuff, then a separate bus that comes (nearly) directly off of the battery (also comes off the daughterboard), although there is a cap/diode arrangement on the DB between the battery and the 12v bus to provide some sag protecti> This is probably a very basic question, but it is troubling me.
Reply to
The Artist Formerly Known as K

Are you building a switching regulator? 5V from 12V through a linear regulator is a huge loss, (at 500mA, its 3.5W wasted) especially in a mobile unit where battery life and heat issues are a concern.

If the answer to the question is "yes", then ask yourself if you want to build one for each daughterboard. Probably not. Provide 5V through a switching regulator, and then place a LDO 3.3V linear regulator wherever you need 3.3V. Even at 50 mA, you're only dissipating 85 mW -- and 50 mA is a very conservative figure for a 3.3V core microcontroller.

Reply to
Mark Haase

"Mark Haase"

Thinking throughout the day, I think I'll have to.

I figured that out, indeed innaceptable

The problem with the switching regulator is that it is going to be too noise for a few sensors I'm using. Seems like I'm getting to a consensus for building one daughterboard where I have a switching supply from 12V to 6V, and then a LDO vreg on each daughterboard to 5V or 3.3V, this way I accomplish a couple of things:

  1. I effectively increase the overal efficiency of conversion/regulation
  2. I get a 6V line for my servos (although I need to consider power consumption requirements if I'm going to drive the servos directly from the switching PS output)
  3. Each daughterboard will be completely independent regarding power supply and power protection.

I was planning to use the ST L5973AD as a switching regulator. It seems simple to implement and doesn't need a bag full of extra components, but it provides up to 2A current. I don't know if that's gonna be enough for my sensors AND servos.

Cheers

Reply to
Padu

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