L-Adapter

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InSides

Member
Joined 2004
jimk04 said:
I have recently changed from 12v trafo to a 9v for my 5v L Ad powering Rpi 3b. I found the sink on Q2 was getting quite hot with the 12v...touchable but definitely very warm. Still warm with 9v but I am happier!
Click to expand...

I thought that might be the case.

I am planning to mill a full "cover" for the PCB (and populated parts, obviously) out of aluminium so that it looks like a single block. Q2 would be attached to the cover (and the PCB upside-down) so that the entire cover acts like a heatsink.

Heat management should not be that big of an issue - but still want to make sure the PSU operates optimally.
 
C

CallMeMike

Member
Joined 2016
InSides said:
Hey Salas, many thanks for what is poised to be a great PSU option for the RPi4.

I have a few boards on the way, and as I am slowly gathering parts (I am having the PSU built by someone much more experienced than myself), a question:

I have on hand an encapsulated, double shielded 2 x 12V @ 50VA toroidal transformer. I understand that within the guide you recommend 9V transformers for a 5V (well, 5.1V output) - but is there any chance to use this transformer?

My initial plan is to have 2 PSU's built in the same enclosure with the same transformer - one for the RPi4, the other for an optional USB isolator if the need arises.

I'd like to be able to use this transformer, especially since getting a new one will delay the build significantly, but do not want to compromise on the PSU.

Any thoughts? Thanks!
Click to expand...


It is quite likely that you may need to upgrade the heatsinks for dissipating the increased heat; in your case it may be a better solution to use your choice of transformer (it seems to be a quality one) and larger heatsinks if the enclosure you have in mind allows it.
 
I

InSides

Member
Joined 2004
Much appreciated all. Once I have the boards in hand, will post here a CAD of the "cover" which should act like a heatsink.

One more sanity check before I go ahead with milling, if you will.

Also, may be a stupid question - but are there any issues with mounting the boards, and with that, the PSU, upside down?
 
I

InSides

Member
Joined 2004
Salas said:
All the electrons are going to fall out! Naah no issues.
Click to expand...

Hey I warned it may be a stupid question! :D

In all seriousness though, I was wondering about the fuse clip mostly - but I take it that should be just fine.

Now the only thing that remains is to locate 6,800uF capacitors which work well for the circuit according to recommendations (35V, 105 C), but are still shorter than (or equal to) 25mm (20mm would be ideal, but they don't seem to exist).

Trying to cram all this in a low profile case, but if all else fails, I will have the PSU cover stick through the top like the transformer does.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
If it isn't going to be too hot inside the box 85C capacitors aren't an impossibility. Lifetime is stated in hours at nominal C. Rule of thumb is it doubles with each 10C less. A 1000h 85C cap is expected dry in 8000h at 55C for example.
 
I

InSides

Member
Joined 2004
Salas said:
If it isn't going to be too hot inside the box 85C capacitors aren't an impossibility. Lifetime is stated in hours at nominal C. Rule of thumb is it doubles with each 10C less. A 1000h 85C cap is expected dry in 8000h at 55C for example.
Click to expand...

Got it.

Vertical height is exactly 38mm. With, say, 6mm spacers and 2mm board height, I still have 30mm above the board, so I can go with 25mm capacitors (CDE makes some) and will mount the PCB the right way up.

This means no cover for the PSU, but I can mill a proper off-board heatsink for Q2. I may still go for board level heatsinks on the diodes, just to be on the safe side.

Proper ventilation on the top cover, of course.
 
merlin el mago

merlin el mago

Member
Joined 2009
Paid Member
Salas could the L-Adapter power mine laptop 20V 2.25A, I ask because is in the edge of maximum voltage output?
 

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Z

zOr7gA8

Member
Joined 2020
Newbie questions

hello, I'm a newbie in diy-audio. I want to build a L-Adapter for my audio-device. ('ve seen the group buy thread ;-) and have questions.

-> I use a PI3A+ which needs 5V 2,5A with a diy-DAC connected via GPIO/hat.
1.) which specs should the input psu have. I've read 9V would be good!? how much Ampere should the input unit have?

2.) which output power from L-adapter is best for my system? Have read voltage should be about 5,1V and Ampere can be up to 30% higher than needed. so 3A should be fine?

-> Several options for power input. I can give power input to PI via micro-usb (and feed DAC). I can give power input to DAC (and feed PI). Or I can give seperate power input to PI and DAC.
3.) which way of power input do you recommend?

-> I think clean power to PI (for whole system) is good. maybe better is, dirty power to PI and separate clean power to DAC.
4.) do you think it needed to use 2 L-adapters for separate clean power supply for each PI and DAC?

Thx in advance.
 
J

jimk04

Member
Joined 2018
Paid Member
@z0r7

I can recommend powering the Pi and dac separately but also using an isolator...available from Ian Canada or Allo. Both available form Audiophonics or though Ian's group buy .

Powering the pi through the micro usb is not optimal.

Recommend an L adapter for your Pi and another suitable psu for your DACs requirements.
 
Z

zOr7gA8

Member
Joined 2020
jimk04 said:
@z0r7

Recommend an L adapter for your Pi and another suitable psu for your DACs requirements.
Click to expand...

Thanks for the answer.
In my understanding the L-Adapter gives "clean" power out of an ordinary psu. You recommend to feed the pi with the L-adapter, and the DAC separately, but not necessarily with usage of L-Adapter. Do I get it right?

I thought linear low noise power for the DAC is more important than for the PI!?
 
R

ricyuyc

Member
Joined 2006
zOr7gA8 said:
Thanks for the answer.
In my understanding the L-Adapter gives "clean" power out of an ordinary psu. You recommend to feed the pi with the L-adapter, and the DAC separately, but not necessarily with usage of L-Adapter. Do I get it right?

I thought linear low noise power for the DAC is more important than for the PI!?
Click to expand...
If you have good quality output equipment, I think it is worth to feed the DAC PS rails with independent supply, i.e. analog side by ultrabib and digital side by reflektor-d.
 
I

InSides

Member
Joined 2004
So as the PCB's are on their way to me, I've been working through the parts list and was able to find almost everything at Mouser, which is pretty much the only option that would send most (if not all) parts to me.

Two items are currently out of stock:

1. The Kingbright LED graph is out of stock until late August it seems. But locally I have found a different Kingbright model (DC-10YWA). Is it OK to use this one as opposed to the DC-10EWA? Alternatively, could you suggest a suitable alternative currently in stock at Mouser?

2. Also, the multi-turn pot is out of stock at Mouser (500R mutli-turn 3296Y Bourns style). Could anyone please suggest an alternative currently in stock at Mouser?

Thanks!

EDIT: It seems there is an identical Bourns pot at Mouser currently in stock, with the sole exception the packaging is not tube, but cut tape reel. Slightly more expensive, but that is fine - can anyone confirm this pot is the same, albeit different packaging and can be used?
 
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