3x powersupply for rpi

[pistollero]

[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 4561 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