AC-DC power supply

Thread Starter

MacMcD

Joined Feb 4, 2024
7
Hello,
I have just joined the website. I am fairly new to electronic theory and design, but like to build projects. I have a few amp kits, preamps, dacs, speaker projects on the go. I am looking for help with the following.

I am going to power the digital side of an I2S over USB board from 2 external supply's. I need 2 AC-DC power supply's powered by 9VAC transformer secondaries. The output DC is +5V 400ma draw for one and +5V 100ma draw for the other.

So to start out with my first questions on this forum:

1. When looking at online AC-DC power supply's to purchase, they are +/- DC outputs. Is it possible to use only the + output of these power supply's ?
2. If the answer to question #1 is "No", would any member have access to gerber files that I could send to a pcb fab shop. I was thinking that LM317T would be a good choice for the application.

I hope I have given enough information, thanks for the help,
MM
 

MrChips

Joined Oct 2, 2009
30,794
Welcome to AAC!

If we are talking about wall adapters (bricks, walwarts, power adapters, etc.) there are two designs.

1) Transformer adapters. These tend to be bulkier and heavier.

1707314527402.png

2) Non-transformer adapters. More commonly used as USB chargers.
1707314713417.png

The photos shown above are not representative of all wall adapters. There are many other styles and types.

In general, a single voltage supply will have an output plug. This is often a barrel connector of different styles and sizes.
1707314924399.png

1707315015106.png


The label on the adapter will indicate the voltage and current output as well as the polarity of the output connector.
Note that the current rating is the maximum current that the adpater can supply. The actual current output will depend on the load. The load will only take as much current as it needs.

+ and - label does NOT suggest that one wire is positive and the other is negative. It means that one wire is more positive than the other wire. In other words, the voltage rating is a relative value. In the above example, the positive wire is 6V higher than the negative wire.

To answer your questions,

1) No. You need to use both wires.

2) If your two loads require 400mA @ +5VDC and 100mA @ +5VDC, you do not need two supplies.
All you need is a single +5VDC supply that can provide a minimum of 500mA.
A good choice would be a +8VDC @ 600mA and use a 3-terminal 5V regulator.

Better still, use a single USB charger that is already regulated to supply +5VDC and in excess of 500mA.

1707315773144.png
 

Thread Starter

MacMcD

Joined Feb 4, 2024
7
Thanks for all the replies,
I guess I did not explain my needs very well. I have an r-core transformer that has 2 X 9VAC secondaries. I would like to build 2 x AC-DC single rail power supplies. The 2 power supplies need to be separate in all respects. The 2 power supplies can have the same DC output values, for example +5V @ 500ma. DC type wall warts do not satisfy my needs as I have a transformer.

Would anyone have a circuit that they have built using simple components that would help me out.
 

MrChips

Joined Oct 2, 2009
30,794
Thanks for all the replies,
I guess I did not explain my needs very well. I have an r-core transformer that has 2 X 9VAC secondaries. I would like to build 2 x AC-DC single rail power supplies. The 2 power supplies need to be separate in all respects. The 2 power supplies can have the same DC output values, for example +5V @ 500ma. DC type wall warts do not satisfy my needs as I have a transformer.

Would anyone have a circuit that they have built using simple components that would help me out.
Why do you need two +5VDC supplies when one will do?

Here is your basic +5VDC regulated PSU. Use your 120VAC to 9VAC transformer.

1707321410127.png
 

BobTPH

Joined Jun 5, 2013
8,938
How many wires in the secondaries? If it is 3, you cannot make two separate isolated supplies. If it is 4, than make sure the two for one supply have no continuity
to the two wires for the other one.
 

MisterBill2

Joined Jan 23, 2018
18,461
The five volt supply shown in post #5 will supply your needs very well if you use your 9 volt transformers instead of the 12 volt one shown. It will even be a bit more efficient. Just duplicate the circuit to provide the separate isolated supply.
Foe the discussion of the wall type supplies shown, the positive wire is the source, the negative is the return. Basic circuit theory is that no current will flow until there is a complete path around the loop.
 

boostbuck

Joined Oct 5, 2017
510
Per post #6, the world is swimming in 5V phone chargers, most of them are about 1 amp these days. Is there some reason you don't want to use these?
 

Thread Starter

MacMcD

Joined Feb 4, 2024
7
Thank you for all the replies. @ MrChips: I need 2 x +5V supplies that do not share anything. @ MrBill2: thank you for your knowledge. @ all the DC wall wart replies, I am using a r-core transformer with 4 independent secondaries for powering the dac main board and the digital I2S over USB board. I already have a power supply unit for the main board. The idea of using 2 extra DC power supplies to power the digital part does not appeal to me, but thank you for the information.
Best regards,
MM
 

MisterBill2

Joined Jan 23, 2018
18,461
The reason for avoiding chargers is first, there is no need for battery charge power to be low noise, and second, there is no need for it to be isolated from the mais iput line, which could put mains AC on one of the outputs. So there are two good reasons, not the only ones, but certainly conditions able to cause problems.
 

MrChips

Joined Oct 2, 2009
30,794
Thank you for all the replies. @ MrChips: I need 2 x +5V supplies that do not share anything. @ MrBill2: thank you for your knowledge. @ all the DC wall wart replies, I am using a r-core transformer with 4 independent secondaries for powering the dac main board and the digital I2S over USB board. I already have a power supply unit for the main board. The idea of using 2 extra DC power supplies to power the digital part does not appeal to me, but thank you for the information.
Best regards,
MM
Can you give me your reasons why the two supplies have to be isolated from each other?
I cannot think of a good enough reason myself. I can see a 12VAC CT transformer filling your needs.
 

Thread Starter

MacMcD

Joined Feb 4, 2024
7
MrChips,
A person can power the USB section of the JLSound card fron existing USB bus (computer), and then the oscillator and reclock section can be powered from the psu that was used for the mainboard. Nothing wtong with this and many have done this. Only problem is hash introduced from your USB bus. This is why some people have gone to separate supplies, one for the analog portion and one for the digital portion of the JLSounds board. No communication or interference with each other. Here are some quotes from some members on the diyAudio forum that have used separate supplys.

1. This member took 2 bipolar psu's and cut them in half to get 2 x +5V single rail boards.
Quote 1: Finally used modified PSU2 for (2x5v) for Jlsound board. Separate for digital and analog. Jlsound spend less than 400mA as it specified but 1963 regulator become very hot. Didn't expect but this regulator require really big heat sink for currents much bellow maximum.

Qoute2: The real deal is a 7- 8VAC secondary for XMOS (analog) part and another secondary 7-8VAC for the oscillator part. Hence the need for 2 supplies.

Qoute3: Question:
Can the remaining 2 x 9V secondary's be used to power the JL Sounds board, as I do not want it powered from my PC ?
Yes. Take a raster board and make two separate power supplies.

One is 5V 400mA (with a large heatsink) and one 5V 100mA with a smaller heatsink. Use separate secondaries, the 5V 400mA should be galvanically isolated from everything else, ground it to the chassis via a 100nF 100V capacitor. The other 5V 100mA should be grounded to the common GND of the other power supplies.

I used LM1117T-5.0 LDO voltage stabilizers, but any fixed or adjustable TO220 stabilizer will do. For 5V 400mA and LDO voltage stabilizers the transformer secondary must be at least 7VAC 600mA. If the stabilizers are not LDO then at least 9VAC 600mA. And use schottky diodes, 2-3A for 400mA, 1A for 100mA.

Quote4:
Please make sure that the USB and oscillator/reclock is powered separately to have optimal performance.
Details on page 3 of the JLSounds user guide.

This si about all I know about it. If you go to diyaudio and look at the thread DAC AD1862 Almost THT I2S input NOS R-2R and have a look at pages 398 to 400 for info.
Regards,
MM
 

MisterBill2

Joined Jan 23, 2018
18,461
The main reason for choosing to have separate power supplies, aside from providing enough capability, is to provide isolation between the circuits being powered. Coupling becomes an issue when loads vary the current draw during operation, because neither power supplies nor wiring have actual "Zero" Internal impedance. It is that effective impedance that couples the voltage variations between the different circuits, causing undesired operation.. It is also a "Real World" problem that seldom appears in most simulations, and so is missed as a problem source sometimes.
 

Irving

Joined Jan 30, 2016
3,878
A single supply with suitable filtering will suffice. The main reason for duplicate supplies for analog and digital portions is to reduce noise in the analog side from switching noise on the power supply on the digital side. This is usually the result of poor/inadequate power supply decoupling on the digital side and introduction of ground loops due to poor routing of digital and analog grounds. The two diagrams below showcase the issue.

1707394602854.png
 

BobTPH

Joined Jun 5, 2013
8,938
Are you sure the two sections you are powering are isolated from each other? Because if there are signals passed between them without using galvanic isolation, your two supplies are no longer isolated.

Edit: can you post a link to the board(s) you are using so we can get an idea what you are talking about.
 

Thread Starter

MacMcD

Joined Feb 4, 2024
7
Here are a couple of posts to explain the concept of 2 independent supplies.
NIXIE62
Separate galvanically isolated power supply for the XMOS part of the JLS card. The second part of the JLS card should have a a separate power supply and a connection to the DAC GND. These power supplies must have two separate secondaries.

ra7


So, you are saying use two supplies: one for usb portion and one for clocks, correct? And tie the clocks ground to dac gnd? Wouldn’t that be through the i2s lines? Each one has a gnd connection and they are all tied together on the TDA board.

My plan is to build at least one supply first for the clock portion.

NIXIE62
That's right, one power supply for the USB part and one for the oscillators. There is a galvanic separation between them, if you have only one power supply for both parts, you do not have a galvanically separated PC from the DAC. The oscillator part is grounded through the I2S connection on the DAC board. There is no need to make another GND connection because it is a ground loop.

That power supply for the USB part, if you want to keep the galvanic isolation, must have a separate secondary on the transformer. That part is grounded to the chassis via a 100nF capacitor, it is preferable to have AC GND for high frequencies, but it is not mandatory.

Only one power supply for the oscillators is possible, and the USB part is powered from the PC. But it is best to have both separate power supplies, because the quality of the power supply from the PC is not great, there is usually a lot of noise.

ra7


JLSounds board now working with two independent regs, one for usb and other for the clocks. Sounds much better. Earlier I found it to be bass heavy and somewhat harsh, which was surprising considering it is driving the TDA1541. It appears it is sensitive to the USB supply as much as the clocks supply.

The regs I am using are simple LED mosfet followers, where an LED string on the gate is used to set the voltage out.


Here is a picture of the DAC and JLSounds card with no external psu's.

IMG_3070.heic.jpeg

Here is a pic of a psu that is powering the one part of the JLSounds board. The other source of power to the board is from the DAC board. This is not how it should be. Should be either no independant supplies like the image of the basic dac, or 2 independant supplies (ie: not half way).

IMG-20230817-WA0000.jpeg


I am working with some buds on some psu's on another forum, So not sure how much I will be back here on this subject. I hope that the latest information I have provided helps to give a more clear understanding of the process. Thank you all for your knowledge and time sofar
Regards,
Myles
 

MisterBill2

Joined Jan 23, 2018
18,461
My experience in building industrial testing machines has been that it is less expensive to use separate power supplies for the digital section and the analog (linear signals) section. The time and grief of looking to see where things went wrong is vastly more than the cost of the separate supplies, in addition to being required by the plant equipment specifications folks. An additional benefit is that using separate supplies allows setting the voltage of each at an optimum level.
 
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