SMPS question

[noofny]

Hi all! I've been reading everyones helpful input in regard to using SMPS to power their MB's;

http://www.midibox.org/forum/index.php/topic,2081.0.html

http://www.midibox.org/forum/index.php/topic,10921.0.html

Basically I want one that provides 12v for goosneck lamps and 5v for MB. There's 2 that sell here in Australia via Electus/JayCar which look OK but I know NOTHING about this subject, so was wondering if anyone could comment on these specs to help a decision (or talk me out of it altogether!). My MB is 2 MB64e's linked so no motofaders or anything too fancy, seems 1-2 Amps will be enough for the 5v rail to power the MB's so there should be plenty with these?

Soanar - 60W - $65 AUD (34 EUR)

Output 5v, Tolerance +-10%, Ripple/Noise 75mV, Current 0.3-6A

Output 12v, Tolerance +-10%, Ripple/Noise 150mV, Current 0.2-4A

MeanWell - 60W - $80 AUD (42 EUR)

Output 5v, Tolerance +-2%, Ripple/Noise 75mV, Current 4A

Output 12v, Tolerance +-2%, Ripple/Noise 150mV, Current 3A

 

Am getting a lot of help from this forum and loving my first MB project so far!  :)

-Mike

[lylehaze]

Welcome!

Speaking in general: Switching supplies are great for digital projects, but can be a source of electrical noise if you are building an analog project (audio).

I'm not saying that you can't use switching for audio, just that you may have noise issues to deal with.

Getting back to your specific application, The applications you mentioned (MB64E X 2 and lamps) should have no problems. The MB64E is a digital project, and the lamps are, well, they are lamps.

One thing to watch out for. Many SMPS supplies have a minimum current that must be drawn for the regulator to work. One of your examples even calls it out in the specs. You will need to make sure that you always load the supply by at least that amount. This can suusally be done with a few big power resistors (which may get warm). There are Ohms Law calculators on the web that will help sort out the correct values.

A popular trick for a cheap "bench" power supply is to convert an old PC supply. Just as above, you will need to "load" the +5 and possibly the +3.3 volt supply to make it work. Also, If you're using a PC supply, be SURE to fuse your project, as those supplies can deliver enough power to do some real damage before they trip themselves out.

Have Fun,

LyleHaze

[noofny]

Welcome!

Thanks!

Speaking in general: Switching supplies are great for digital projects, but can be a source of electrical noise if you are building an analog project (audio).

Yes it seems to be that way - lot of people arguing for and against.

I'm not saying that you can't use switching for audio, just that you may have noise issues to deal with.

Thats exactly what I thought. I don't know if anyone can comment on what is classed as 'noisy' or 'acceptable' - would 75mV or ripple/noise on 5v rail and 150mV ripple/noise on 12v rail be considered good/bad, or is this a stupid noob question?

Cheers

[stryd_one]

Thats exactly what I thought. I don't know if anyone can comment on what is classed as 'noisy' or 'acceptable' - would 75mV or ripple/noise on 5v rail and 150mV ripple/noise on 12v rail be considered good/bad, or is this a stupid noob question?

No I think that's an excellent question. I'd like to know the answer too :)

[lylehaze]

It's a perfectly good question, and I won't answer it for you. :-)

Especially in audio, the term "acceptable noise" is an argument in itself. I think Alan Parsons would have a different threshhold of "acceptable" than say  Jimi Hendrix. One made his name by eliminating noise, the other by amplifying it.

So I'll cop out and give an engineers answer. A switching mode supply works (in part) by "chopping" the incoming voltage at a varying dwell angle, using this to adjust the resulting voltage. This turns out to be way more efficient than linear supplies (less heat to dissipate) but it can produce a lot of noise, expecially near the switching frequency. There are some things the designer can do to reduce that noise, but if it's being mass-produced, companies trying to save every penny will reduce or eliminate those "unnecessary" parts.

So, as a designer, the first call is to reduce the emission of noise from the power supply itself. The second call is to adapt your audio circuits with a low-pass filter to further reduce these high frequencies. For something like an ADC (audio digitizer) you might even choose a fixed frequency power supply and filter that frequency in software (though that is a bit extreme).

Another trick is to use a SMPS to feed an "ideal" voltage into a linear regulator. i.e use a 7.5 volt SMPS to feed a 7805. This gives SOME advantages from both worlds, but it's not perfect.

In the end, what is "acceptable noise" is up to each individual. It does make a difference.

As I said before, the MB64(e) does not directly handle any audio (as far as I know) so you are free to use SMPS without any ill effects.

Please pardon my verbose response, but there's always a lot of power supply questions around here, so I try to be as complete as possible in my answers.

LyleHaze

[stryd_one]

my verbose response

Keep em coming buddy!

[noofny]

Indeed keep em coming - I'm learning so much in such a short time from this forum (and the project).

Thanks again LyleHaze for taking the time and write such an awesome response.

All the switches, pots and LED's arrive today so it's going to be a good busy weekend!  8)

-Mike