[sdiy] anyone tried this SMPSU?

Ben Stuyts ben at stuyts.nl
Thu Feb 18 11:14:47 CET 2021


I’ll try to give a 10 km overview… Conducted emission is just one aspect of EMC (electro-magnetic compatibility). Broadly speaking you have:

- emission: anything unwanted that comes out of your device. This might affect other equipment around it. TV sets, pacemakers, airplanes...
- immunity: anything that comes into your device and affects its operation in a negative way. Crashing cpu’s, noise on the audio output, etc.

Both of these can be subdivided (again broadly!) in:

- conducted: this comes in or goes out via the cabling. An SMPS might throw noise out on the AC line, and that can affect other equipment. Or you get noise through the AC line into your device, and that manifests itself as e.g. noise on the audio output or CV.
- radiated: this comes in or goes out of your device via the air. That CPU clock line on your board is a nice antenna which transmits e.g. 25 MHz plus all its harmonics. Or the other way around: a cell phone nearby might be received by your board, the signal is rectified and you hear those familiar sounds in your audio path.

Conducted and radiated noise are also related: noise coming out of a device via the power supply lines, can end up being radiated emission because the power supply lines are basically antenna’s.

So these are four different things to check and take care of. Some can be solved by shielding (radiated), others by filtering (conducted). The one I mentioned below was a specific case of the Mean Well power supply throwing stuff back out on the AC line. A common mode filter (a common mode choke coil) was enough to solve this problem. I often use this series: https://www.we-online.com/catalog/en/WE-LF. Sometimes additional ferrite is needed in the cable: https://www.we-online.com/catalog/en/pbs/emc_components/ferrites_for_cable_assembly.

But that whole system required mechanical shielding as well, to cope with radiated aspects.

Disclaimer: I am by no means an expert in this subject, but I do have experience with our products having to comply with EMC regulations. So I often work with specialists and test houses on this subject.

Ben


> On 17 Feb 2021, at 15:43, ColinMuirDorward <colindorward at gmail.com> wrote:
> 
> Conductive shielding is something I've never implemented, great idea to fab PCB for the job, I'll give this a go. I thought a conductive shield would need to be grounded, how can it do anything if it's just a floating piece of metal? Well I have seen people with tinfoil hats in the movies.
> 
> I looked up "conducted EMC" and got a little lost in all the other EMC acronyms. What does it stand for here?
> 
> Also a great idea to use these as replacement supplies for dying gear. I actually have an MPX1 and a DX7S, so maybe I'll need a few extras one day! In more dire need of repair is my JX-10 supply, which is suffering from a (mechanically) buzzing transformer.
> 
> Is anyone regulating SMPS down for example from 15v to 12v? My understanding is that HF noise will pass right through the lm317, etc, and yet I see it is very popular to use SMPS brick/wallwart connecting to a eurorack case which then uses linear regulators to derive 12v. I was just looking at the behringer euro supply, and I think it actually uses two SMPSUs: one in the power brick, and then another in the module itself. I'm sure it works, but is that a little goofy?
> 
> Thanks folks!
> 
> On Wed, Feb 17, 2021 at 5:25 AM Ben Stuyts <ben at stuyts.nl <mailto:ben at stuyts.nl>> wrote:
> I meant to say: they offer a good trade-off between performance, reliability and *price*
> 
> > On 17 Feb 2021, at 10:31, Ben Stuyts <ben at stuyts.nl <mailto:ben at stuyts.nl>> wrote:
> > 
> > 
> > 
> >> On 17 Feb 2021, at 04:10, Brian Willoughby <brianw at audiobanshee.com <mailto:brianw at audiobanshee.com>> wrote:
> >> 
> >> Mean Well aren't perfect, but they do quite well.
> > 
> > We use quite a few MW psu’s in my company because they offer a good trade-off between performance and reliability. The one issue though during design that always comes up is conducted EMC. If you have any noise on the DC (e.g. from a CPU clock) it will go straight out to the AC side. We usually (now habitually…) have to add some form of common-mode filter on the AC side.
> > 
> > Ben
> > 
> > 
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