Low noise 5VDC power supply design

[BjornKarl]

Hi,
I’m not good at circuit design but I can use a soldering iron. I have a high-end audio device which is currently operating with 2 Li-Ion batteries. I constantly forget to charge the batteries si I’m looking to replace them with a line operated DC supply. The output from this supply shall be 5VDC with a current output of about 100mA. But, the output must have ultra low audible noise, approaching that what I get from using the battery. It must also be well filtered to eliminate hum. Can anyone point me in a direction where I could possibly find a circuit diagram with appropriate component values for this use?

I have looke all over to find a ready made board for this but can’t find anything other than cheap stuff from China which of course have no specifications to support the claims. I’m grateful for any advice I can get on this.

[rooppoorali]

Have you tested this circuit ever? https://www.theengineeringprojects.com/2015/04/how-to-design-a-dc-power-supply-in-proteus.html

Among the ready-made ones, this one has good reviews: https://allo.com/sparky/shanti.html

There are 2 options here. 5V,3A and 5V,1A. 5V,1A means, it can output Maxium 1A current. If your requirement is less, you can still use this power supply.

[Vovk_Z]

But, the output must have ultra low audible noise, approaching that what I get from using the battery. It must also be well filtered to eliminate hum. Can anyone point me in a direction where I could possibly find a circuit diagram with appropriate component values for this use?

I'm not sure there is a circuit diagram which may give 'ultra low noise' itself without some additional knowledge how to make an ultra low noise devices.
I would recommend to study some book about how to achieve low noise, for example, 'Noise Reduction Techniques in Electronic Systems by Henry W OTT, and 'High Speed Digital Design: A Handbook of Black Magic', and similar. Somewhere there was a topic about literature on this topic.
eevblog.com Book about noise?

[Terry Bites]

Low noise design requires careful layout/ wiring and good filtering on the input and output. Adding an LDO after the ouput will reduce ripple and noise.
You will probably need a shielded box or can to stop radiated fileds coupling into your deleicate circuit. It will not be easy to get right without the electical know-how.

See this example problem solving https://recom-power.com/en/rec-n-very-low-noise-filter-for-isolated-dc!sdc-converters-46.html?0

Here is a deep dive into issues and solutions www.ti.com/lit/pdf/slyp709?keyMatch=SLYP709

[mariush]

You could just go old school with an AC linear power supply

They make small transformers that you can mount on a prototyping board .. add a fuse, a bridge rectifier,a smoothing capacitor and a linear regulator to regulate to 5v and a small capacitor on output of this regulator (or capacitor - inductor - capacitor as a pi filter) and you have a linear power supply.

Pick a transformer that outputs 8..12v AC  because after rectification using a bridge rectifier, you'll have a DC voltage with a peak equal to Vdc peak = Vac x 1.414 - 2  x (voltage drop on diode inside bridge rectifier)
So for example, for a 9v AC output transformer, you'll have Vdc peak = 9vx1.414 - 2 x 0.8v  = 11v
If you use a plain linear regulator, such regulators usually require that the input voltage must always be above the output voltage by at least 1 - 1.5v so let's make sure it will by adding a capacitor after the bridge rectifier.
You say you need around 0.1A so let's calculate things for a maximum of 0.25A of current.

This formula approximates how much capacitance would be the minimum to use to always have the voltage above some threshold :

C = Current / [ 2  x AC Frequency x (Vdc peak - Vdc min) ]

With the 9v transformer example above we can put the values in formula C = 0.25A / 2 x 60 Hz x (11v - 7v)   = 0.25 /  120*4 = 5.20e-4  Farads or around 520uF  so to guarantee at least 7v before the regulator even if your circuit consumes 0.25A, you would need at least 560uF.
Considering you're estimating 0.1A, you can probably go with a standard value of 470uF (should be rated for at least 25v).

For the actual linear regulator, it won't really matter ... a 7805 would work... and have a small 100uF 10v (or higher) rated capacitor on the output of this regulator.

[Peabody]

For an audio device, I wonder if a switching supply might be a better choice.  If it oscillates at 500KHz or more, perhaps the remaining ripple would just be at a much higher frequency than you  could hear.  But I'm no expert.  Maybe it doesn't work that way.  It just seems that with a linear regulator it's hard to get rid of mains hum, which you defintely can hear.

[tooki]

For an audio device, I wonder if a switching supply might be a better choice.  If it oscillates at 500KHz or more, perhaps the remaining ripple would just be at a much higher frequency than you  could hear.  But I'm no expert.  Maybe it doesn't work that way.  It just seems that with a linear regulator it's hard to get rid of mains hum, which you defintely can hear.

I'd say you've got it precisely backwards. It's easy for a linear regulator to get rid of hum. Trivially easy. If you're getting audible hum, it's not because of the regulator, but a ground loop.

Switching supplies can be OK, but they are often very noisy. It's rarely that they switch at an audible frequency, but rather that there are audible-frequency harmonics that can get spewed out into your circuit (both in ripple and as electromagnetic interference induced into nearby circuits). And they can still cause ground loops.

And finally, any amplifier worth its salt is fairly impervious to power supply ripple. In the past, it was actually quite common to use unregulated power supplies for the power amplifier stages. Just rectified and smoothed with big caps.

[BjornKarl]

Thank you for your inout. I’m already very familiar with the ALLO Shanti and it is a very good one. But the supply also has a 5V/3A included which I do not need. Also, the Shanti is a complete standalone unit which takes up a lot of space. I’m looking for a circuit that I can incorporate together with  a streamer and a DAC in my own enclosure. And I already have 9VAC available.

[TimFox]

If you decide to go the old-fashioned transformer-rectifier-filter power supply route, I highly recommend PSUD II freeware from Duncan to design the rectifier section.
Note that the software models the transformer by no-load voltage and equivalent secondary resistance, but manufacturers specify them by loaded voltage at specified load current.
https://groups.io/g/duncanampspsud

[BILLPOD]

Any USB charger would work for this, and you must have several, as everyone must have.  Cut off the USB plug and strip back the wires a bit.
Attach whatever connectors you need to power your audio device to the red and black wires.

[beatman]

i have the same problem about.i want to replace the two stock switch mode psu,s from two motu devices.i just by one 18v -3a linear laboratory power supply with just 0.5 millivolt ripple .i replace the caps inside with good quality lock the knob to 15.2v and power the two units ecxelent solution.better sound overal

[MathWizard]

Yeah I have a stereo with an unregulated 18V from a transformer, it feeds all the op-amps, etc, and a 7806 for a reference voltage. I guess it's all common mode-noise to the op-amps, and mostly cancels out at the output.

The only real amount of 120Hz hum it ever has is when I had a ground loop by connecting the return path of 1 PCB to the wrong gnd point, it should be a star-gnd.

[jc101]

I have a high-end audio device which is currently operating with 2 Li-Ion batteries. I constantly forget to charge the batteries

Get a second set of batteries, keep one set charged and swap them over as needed - so there is always a charged set to hand?

[radiolistener]

you can use usual linear regulator IC. For example, you can use some popular LDO from ST or other manufacturer.

But it's not clear what is your noise level expectations?
If you're needs ultra low noise, there are also more expensive ultra low noise linear regulators, for example LT3042.

What is your noise level requirements?

[radiolistener]

But, the output must have ultra low audible noise, approaching that what I get from using the battery.

If it's for a hi-end audio DAC, I think LT3042 solution will be good enough.

But such design also require proper shielding and ground layout, otherwise bad PCB design can kill profit from a good regulator IC performance due to RFI and near field coupling.

[tooki]

I very much doubt LT3042 levels of performance are necessary, and given that the OP isn’t that experienced in electronics, the PCB layout requirements of the LT3042 to achieve its full performance are likely out of reach.

Besides, we don’t even know if the device needs unusually clean power, or if it’s just a phoney-baloney “audiophile” “requirement” rooted only in superstition.