Single power supply with multiple linear regulated outputs

Thread Starter

Littlegee

Joined Mar 25, 2020
14
Hi can someone help me please, I would like to create a linear regulated power supply unit using a single 240v 50hz AC toroidal transformer with 4 x 5v linear regulated power supply PCB's. I see DIYAUDIO have some super regulator boards that you can build linear regulated voltage supplies from. I want to power the following items.

1. Chord Qutest DAC - 5v 2.1A (As rated on the SMPS)
2. Chord HUEI phono stage - 12v 2.1A (As rated on the SMPS)
3. JCAT USB card FEMTO - 5v 1A minimum
3. JCAT NET card FEMTO - 5v 1.5A minimum

Is it possible to use 4 of these boards, 1 for each regulated linear power supply for each of the above supplies, all powered from 1 toroidal transformer?
 

KeithWalker

Joined Jul 10, 2017
1,225
We need a little more information before we can give you any real answers to your question.
What secondary windings does the transformer have and what voltage and current are they rated at?
Regards,
Keith
 

Thread Starter

Littlegee

Joined Mar 25, 2020
14
I have not selected a transformer yet, that will be worked out based on the other components voltage drops and required power supplies if possible with a single transformer? I am a newbie and learning as i go along, from what I understand so far is that these printed PCB's can be adapted with the correct components to supply a linear regulated power supply both POS, NEG or can be split to use just the POS board. In which case can i use 4 of these boards powered by the secondary windings of a single stepdown transformer? Is it possible to get the required voltage outputs and currents using this particular board and components? Thanks for your response.
 

dl324

Joined Mar 30, 2015
11,573
Given that you want a 12V power supply, you should use switching regulators for the 5V. You could connect all three 5V devices to a single 5V supply. If the secondary voltage is sufficiently high, you may want to use a switching regulator for the 12V supply too.

Have you considered using a computer supply? They're relatively inexpensive and every old computer has one.
 

Thread Starter

Littlegee

Joined Mar 25, 2020
14
I want to steer away from switch mode power supplies as this creates unwanted noise especially since I am powering some very sensitive equipment. I currently have a Wells Audio Headtrip 2 Headphone amplifier which is picking up a really bad humming noise from the DAC's SMPS no matter where I power it from in my studio along with some other ground loop hum signals. I have just built a fanless media server which I will build another LPSU to power once I have established and built a good LPSU for the above mentioned components.
 

dl324

Joined Mar 30, 2015
11,573
I currently have a Wells Audio Headtrip 2 Headphone amplifier which is picking up a really bad humming noise from the DAC's SMPS no matter where I power it from in my studio along with some other ground loop hum signals.
That problem wouldn't be caused by high frequency noise in switching regulators. You should be tracking down the ground loop(s).
 

Thread Starter

Littlegee

Joined Mar 25, 2020
14
Ground loop I already identified and removed with a ground loop isolator circuit device, the hum from the SMPS for the DAC only exists when it is powered and disappears when removed. Having the 4 linear power supply boards in one chassis will be ideal and convenient.
 

dl324

Joined Mar 30, 2015
11,573
Having the 4 linear power supply boards in one chassis will be ideal and convenient.
I don't know what's on these power supply boards you're referring to, but you could also just hang 4 linear regulators on the rectified output from the transformer.

Can't give any meaningful suggestions until you know what the secondary voltage will be.
 

Thread Starter

Littlegee

Joined Mar 25, 2020
14
If the secondary voltage is based on VA's then:

1. Chord Qutest DAC - 5v x 2.1A = 10.5VA
2. Chord HUEI phono stage - 12v x 2.1A = 25.2VA
3. JCAT USB card FEMTO - 5v x 1A = 5A
4. JCAT NET card FEMTO - 5v x 1.5A = 7.5VA

Total 48.2VA
Total current required 6.7A

This has not taken into account voltage drops or any added safety factor

Can you advise me on what transformer would be required, will there be 2v per board voltage drop meaning 8v in total plus the max 12v needed for the 12v LPSU = 12v + 8v = 20v so to get say 6.7A on the secondary would I need something like a 100VA transformer like the attached?
 

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Thread Starter

Littlegee

Joined Mar 25, 2020
14
Actually 6.7 x 20v is 134VA so the next transformer up in the line is the 200VA transformer with 2 x 20v outputs @ 5A so this would give 10A if wired in parallel right, would this work?
 

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Thread Starter

Littlegee

Joined Mar 25, 2020
14
Thank you for your reply, so from what you are saying then it is possible to get 4 linear regulated power supplies off 1 transformer which goes back to my original question. You suggested the VPOT18-5560 9-0-9 toroid here are the specs:

VPT18-5560 Electrical Specifications (@25C)
1. Maximum Power: 100VA
2. Input Voltage: Series: 230VAC, 50/60Hz Parallel: 115VAC, 50/60Hz
3. Output Voltage: Series: 18VAC CT @ 5.56A Parallel: 9.0VAC @ 11.12A
4. Voltage Regulation: 9% TYP from full load to no load
5. Temperature Rise: 45°C TYP
6. Hipot: 4000VAC, Primary to Secondary
7. Efficiency: 88% TYP. @ full load

The output voltage in parallel is 9V @ 11.12A which is fine for the 5v but to get the 12v I assume I would need to boost the voltage somehow? Is it better to boost the voltage for the 12v output needed or better to upgrade the transformer with a higher secondary rating and have regulators dissipate more energy in regulating the voltage down to the required 5v and 12v supplies needed?
 

dendad

Joined Feb 20, 2016
3,602
The output voltage in parallel is 9V @ 11.12A which is fine for the 5v but to get the 12v I assume I would need to boost the voltage somehow? Is it better to boost the voltage for the 12v output needed or better to upgrade the transformer with a higher secondary rating and have regulators dissipate more energy in regulating the voltage down to the required 5v and 12v supplies needed?
Look at the circuit above. It supplies 2 unregulated voltages.
V+ and V+/2
A center tapped transformer with a bridge rectifier is mostly used for +/- supplies, but if it is connected as shown, assuming 9V CT, then you will get (9+9)*1.414 = about 25V, and 9x1.4 = about 12V. This will be a bit different as the transformer 9V out will depend on the mains volts, and there is the rectifier voltage drop to subtract too.
If you can get a 7.5V-0-7.5V one, it will reduce the heating a bit.
The one I mentioned was just the transformer I first found. But if you look further, others will be available.
 

atferrari

Joined Jan 6, 2004
4,095

Thread Starter

Littlegee

Joined Mar 25, 2020
14
Dendad, so what you are saying is the 12v rail is taken from 18v secondary wired in parallel which is rectified and the 3 x 5v supplies come from one half of the the secondary coils which is not rectified as pointed out by Atferrari or the diagram was just a brief overview of how to split the rails? So in actual fact the 9-0-9 transformer would be a good match?
 
ATFerrari;
In the late 1980s I designed this particular configuration supply for a very high volume consumer product. It works.

What is initially confusing, is that the center tap which normally is connected to ground, is now connected to a positive output.

The way to analyze it, is to follow the current thru the diodes and the load. You will notice that the two diodes in the bridge whose anodes are connected to ground, carry the current for both the +5 and +12 regulators.

The diodes in the bridge which are connected to the higher +V, only carry the current for the +12 regulator.
 

dendad

Joined Feb 20, 2016
3,602
The 2 x 9V windings are in series so you get 18VAC. Not parallel.

And the 18V is rectified by the full wave bridge.
Then, the 9V is rectified "push pull" by the 2 left most diodes of the bridge.
Most times the "push pull" rectifiers have the center tap at 0V and use what is the right pair of diodes to give a +ve output, but there is no reason it cannot be used with the diodes the other way to give a "-ve" output. So, here that is done but the -ve out is connected to 0V so the center tap is +ve with respect to that, and that will be the rectified 9V.
Build it up, without the regulators first, and see how it goes.
 

dendad

Joined Feb 20, 2016
3,602
Another way to look at it is to just use 2 diodes for a start, like the 2 right hand ones. Have the center tap at 0V.
Now you will get around +12V, that is 9VAC x 1.414.
Next, connect it up using only the left hand pair of diodes, still CT at. 0V.
The output now is -12V.
Now, with all 4 diodes connected.......
So in effect, you have a dual power supply, +12V, 0V, -12V.
But if you take the CT off the 0V connection and put the -12V one there, you end up with +24V, +12V, 0V.
The voltages are the same, just the reference point has changed.
 

Thread Starter

Littlegee

Joined Mar 25, 2020
14
This is brilliant guys, you are awesome, thanks for your patience so far, as I said I am new to this and learning as I go along. What do you think of the NTE 5322 for the rectifier and LT3086 for the linear DC regulators? Also decoupling capacitors before the rectifier?
 

dendad

Joined Feb 20, 2016
3,602
That rectifier looks ok.
Maybe https://au.element14.com/stmicroelectronics/ld1085v50/ic-reg-ldo-5-0v-3a-to220/dp/1564295?st=3A regulator for the 5V ones,
and https://au.element14.com/texas-instruments/lm1085it-12-nopb/ldo-reg-1-5vdo-3a-12v-3to220/dp/3121991?st=3A regulator for 12V.
You will need quite a good heat sink with all these on it.
The VA you quoted in post #9 is just for the outputs. You will need to almost double that as you are using linear regs.
So, 12V at 2.1A actually will be (18VAC*1.414) * 2.1A = 25*2.1 = 53VA.
Adding all the 5V regs together... = 5V @4.6A.
So, (9VAC*1.414) * 4.6 = 21.5 * 4.6 = 28VA.
Total VA rating needs to be in excess off 80VA, so 100VA transformer is needed.

These numbers are approximations and assuming full load too.
If you take your load VA from the transformer VA, that gives you a bit of an idea what the regulators will have to dissipate in heat.
So, 80 - 48 = 32Watts in heat. You may need a fan on the heat sink.
This is quite a lot! And a full load case.
If you can find a transformer with something like a 7.5 - 0 - 7.5 winding, the dissipation will go down quite a lot.
Some systems use a switch mode supply to drop the power down to a couple of volts above the required level, then a linear reg to get the voltage needed and quiet things down.
If you want to put the time into it, a switch mode supply could be shielded and well filtered to save all that wasted heat.
 
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