Difference between analog/digital PS

[grasshpr]

Hi guys,

Is their any difference between a power supply for analog circuits compared with those for digital circuits?

I would assume that digital circuits don't require very high tolerances for voltage regulation, but I'm just guessing.

 

[rickcr42]

digital power supplies are more about individual voltage pin decoupling and analog supplies geared more for the sonices of the supply

 

[grasshpr]

So rick, I assume that analog power output would be more than sufficient for a digital output source as long as you can supply several independent voltages?

 

[rickcr42]

Yes.You can make a single power supply that is large enough to ahndle all the various voltages required then stage regulate.

say for example the high voltage is for the output stage and it is an opamp design running off +/-12 volts and the digital parts off +/- 5 volts you can build the master supply for 13.4 to 14 volts,and then add local regulators for the sections.
Because of the huge differential between the 14 volts unregulated and the 5 volts regulated needed for the digital section it is advisable to pre-regulate this voltage with a 8 volt "digital master regulator" then do TL431 shunt regs at each digital pin.(plus 100uf/10uf tantalum/0.1uf right at the pins)
This three volt difference is OK and withing the range of the shunts but the larger 14 volts would generate way too much heat in the regulator chips causing short life spans or even failure.

so master supply raw (unregulated) voltage to the output section local vregs and master digital (8 volt regulated) supply to individual local digital vregs is the way for a single power transformer mixed signal supply.

the other option is dual transformers.One digital supply and one for analog

 

[grasshpr]

Thanks for the info rick.

Now I have read from several datasheets that digital ground and analog ground should only be connected at one location. Would you happen to know for what reason?

I'm going to try my hand in using my existing dynahi PS to output a digital supply for a microcontroller project (planning to fancifying my soon to be completed dynalo amp with a nice LCD display

).

 

[rickcr42]

Quote:

Now I have read from several datasheets that digital ground and analog ground should only be connected at one location. Would you happen to know for what reason?

digital ground noise.Easily avoided with a good layout and a single connection point for the digi-analog ground buss.

i will add a couple of links for further info shortly.Sit tight man...............

 

[rickcr42]

Decoupling

http://www.audiocraftersguild.com/Aa...decoupling.pdf

advanced grounding scheme

http://www.audiocraftersguild.com/AandE/2ndxdac.pdf

these 'eval" data sheets show actual board layouts-

http://www-s.ti.com/sc/psheets/sbau016/sbau016.pdf

http://www-s.ti.com/sc/psheets/sbau029/sbau029.pdf

http://www-s.ti.com/sc/psheets/sbau013/sbau013.pdf

http://www-s.ti.com/sc/psheets/slau068/slau068.pdf

and finally some actual layout by sheldon stokes showing two ways to go at the power supply issue :

http://www.quadesl.com/pdf/tube_dac.pdf

http://www.quadesl.com/pdf/cs4329_dac.pdf

http://www.quadesl.com/pdf/cs4329fix.pdf

you can also check the Analog Devices Application notes for mixed signal layout and grounding techniques.See the links section or just google analog devices and hit the front page tab for info.

should be enough to get you started,good luck man

rickmeister

 

[grasshpr]

You truly are the rickmeister! I should start labeling you as the linkmeister as well

Anyway, I was wondering why the DIY forum doesn't have a good links section providing, well, the information you just posted.

Thanks a million rick!

 

[rickcr42]

actually we DO and much of it is there (top of the DIY forum,DIY Big List) but I like to keep it streamlined and on a semi-diet for easy use and have generalised links which lead to other links which lead to more links and leading to.....

but I can see where the recent deluge of questions on digital design mean a big time section update is coming.
the layout side and power supply areas especially

Maybe later today if my brain is still functioning after the huge cookout party I am invited too (I wouldn't bet the farm man.I most likely will be incoherent

)

rickmeister rex

Oh,BTW-do a google on the "Retro DAC" and check out Yuri's site.He has a total perf board DAC layout that really is cool plus save the hassle of pc board design which to be honest is not really needed in most cases for anything other than duplicates.A single "one of' project done point to point or with a vector board works out great in real world practise.

 

[grasshpr]

Sorry for not checking rick. The list is quite long and difficult to navigate. Its like finding a neddle in a haystack, where the hay is serially placed one after another

Anyway, I meant no disrespect to you, since I know you work hard to compiling this list for all.

Thanks for the link about Yuri's site. It will take me some time to digest all this info

 

[rickcr42]

heh,in light of an earlier thread that actually made me laugh man.Thanks for that dude !

I guess I need to get "in there" and shuffle things around a bit and make some new subsections with digital audio being #1 on the list.This to be broken down into still more subsections

Considering the time of year and my free time ramping down drastically as the weather warms up i should have done this over the long gloomy months but it did not seem important so I took a pass :

but I am on it as soon as I get the desire to dive back in.
Really is a big time pain in the a*s sometimes because what you see is not how it looks when I am in there fiddling around then i test each link,check the spacing,etc.A real pain like I said but the time has come so.............