3x powersupply for rpi

pistollero

hondagx35 wroteHi pelliott321,

but what about the 5v supply.

fboe wroteI have made some ekspirement with linear power supplies for the rpi3. First I have powered it with 5v at the gpio, which gave an enormous improvement. But then I removed the "crappy" onboard regulator (for 3,3 and 1.8v) at the rpi board, and powered it direcly at pp8 and pp9. Oh my.... another enourmous improvement in sound

Frank

Hello do you know how many amps are needed for the 1.8 and 3.3 volts?

TommyBoy

Please inform the current usage in 1.8 v
And 3.3 and 5.0 v
So we can plan heatsink size, and correct regulator types.

fboe

it's the chip Pam2306 I have replaced at the rpi 3, and according to the specification for that chip the max current is 1A for 1.8v and 3.3v. I have used that data as a max-guideline.

TommyBoy

aha, if current is under 1A then LT1963 is overkill, it is VERY expensive like all LT products.
better to look at LM2941CT TO-220 it is 1/3 the cost.

fboe

I use the LT1963, because I like the sound of it

-I have tested several regulators and for me this is the best. And the LM2941CT, can't go under 5v in output, so you can't use it for this.
But please try your own choice of regulator

TommyBoy

you are absolutly RIGHT..
good point about the input voltage range of the cheaper LM2941
I had the idea you feed 6V or higher into your audio box,
and then make the 3 low voltages (1.8 3.3 5.0) from a 6V or higher input.
the higher, the better input noise rejection ratio, but also more local heat.

connecting regulators in series is a VERY bad idea for stability,
the total heat loss will be exactly the same, so there is no point in this.

TommyBoy

been playing with this the whole day, just a short Yippee ki-yay
my good thrusty LM2941's works perfectly at any input voltage down to 3V and deliver just perfectly nice and clean 1.8V
so i made a little all lineary power supply for the pi player case, takes 5.5 to 6.5V input
and deliver 5.0 3.3 1.8 as required.
the main input about 6V, is made using transformator, bridge, caps, and huge lin regulator
to night we install and test.

before caps install

with caps and tested and adjusted, same size and same mounting holes as the switchmode unit we are replacing
so it sould be a quick fix.

fboe

Looks great, and I'm looking forward to hear what you think of the sound with this hack

- but how did you manage to get the 2941 under 5v and stable?

And this is my test setup

: IMG_0139.JPG (136.8 KiB) Viewed 5370 times

TommyBoy

>but how did you manage to get the 2941 under 5v and stable?

datasheet is old, from the good-old-5v days, no one had the idea to feed electronics with under 5V,
but off course the part also work all the way down to referance voltage

so no big deal, also tested with a scope, and pulsed load, super performance all the way,
i got a bag og them, and need them tonight, so cant wait..

TommyBoy

here we go installed,

total current at 6V inout is 1.2A to 0.8A with USB harddrive and music playing
the heatsink is not hot at all, so super happy

close up of the connections, be warned : the schematic provided a few posts ago only match correct board hardware version
my PI is another version where this powersupply is changed a bit.
my PI is 3 B ver 2

TommyBoy

my notes about how to connect power supplies
the ic is removed using two soldering irons, then it was easy,

ritsjie1971

Very nice TommyBoy!

Actually I'm working on my linear psu too now. I'm gonna use the LT1963. I have to order the parts and then build it together.

TommyBoy

you are welcome.
please use as SHORT wires as possible, make room for large local caps like my picture show,
DOUBLE check your PI hardware before removing the original switcmode chip,
like measure the 1.8 and 3.3 and 5.0 volts at the locations i have shown.
different PI pcb versions exist, and they have moved the caps and caps numbers a little bit.
also very important to double check the voltages you make with the new regulators,
trim the two low voltages in as accurate as you can +/- 50mV and the 5V a bit to the high side,
like 5.05mV or 5.10V since your USB disk love a little bit to the high side for biggest margin to fail.

Another trick for noise hunters, see the cap near the USB connector, side of board, near IO pinrows ?
it is called C97 on my PI
it is mounted directly on USB power, after the 5V switch and measure system,
add a 1000-2200uF / 16V switch mode super duper grade cap accross this one,
now peak currents from usb disks cant enter your pi.

please share pictures, and results..

ritsjie1971

: 20170218_213347.jpg (145.58 KiB) Viewed 2688 times

My spare time is quite limited these days, as a lot of it goes to my photography hobby

Anyway, I started with the power supply. The main linear supply is finished. With this, I'm gonna feed the stablizers for the 5V, 3V3 and 1V8.

I used a 6V transformer, 4 3A schottky diodes as rectifier, and 4 1500 μF in parallel for smoothing.

ritsjie1971

Rectifier and smoothing elco's.

Attachments

: 20170218_203546.jpg (137.27 KiB) Viewed 2687 times

ritsjie1971

Schematic, so far. No rocket science at all. Power On LED is not drawn here, but it's connected at the output right via a 470 Ohm resistor.

Attachments

: 20170222_163237-1.jpg (46.96 KiB) Viewed 2684 times

pelliott321

Just one question
What is the resistor across the smoothing caps for? What is the value?

ritsjie1971

pelliott321 wroteJust one question
What is the resistor across the smoothing caps for? What is the value?

That's a 2k7 resistor, used to drain the voltage from the caps when no load is connected. Otherwise these caps will keep their charge. So the 2k7 is used to discharge these caps.

TommyBoy

what is your LOADED voltage at v-min measured with a scope ?
to be able to generate 5.00 stable, with no ripple the min pulse must be over 6V
so your trafo deliver too Low voltage,
use a 9V AC trafo and shotkey diodes will give correct range, then add a pre-regulator adjusted to 6V
this way your transfer a perfect DC supply into your critical unit, and this way it can make perfect 5V and all the other voltages,

JohnC

I went down the external DAC route with clean power supply (DIY) with good results. This way, so long it's USB DAC Audio Class 2 compliant, I can have better control of what chip to be used and this method works with Rune very well:

A) The following post has a very simple method to separate the power supply using a Y-split USB cable. It works like a charm:

http://www.head-fi.org/t/634760/resonessence-labs-concero-discussion-review-thead/1320
Go to Post #1326 for the illustration. It works great with iFi iDSD Micro for DSD or DXD files.

B) Another option is to use a DAC that separates the power for you. I personally find the HiFiMeDIY Sabre USB DAC 2 (External PSU) sounds good and have good value for general uses.

C) Lastly, the linear power supply mod for HiFiBerry DAC+ Pro is pretty straight forward. https://support.hifiberry.com/hc/en-us/articles/205732441-DAC-Pro-external-power-supply

John

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