Switching power supplies and DC-DC convertors

[letterbeacon]

Currently I have two linear power supplies in my DIY modular synth. They work well and supply clean +/-15VDC to my system, but they are physically heavy. I'm looking at making my modular more portable for live performances and have started considering switching power supplies.

When I first started building my modular switching supplies were frowned on -too much noise. But I've noticed recently that some modular synth companies are offering switching supplies commercially with good results. Take for example the Tiptop audio Zeus system: http://www.tiptopaudio.com/zeuspwr.php

I think this is how it works:
It takes 15V from regular laptop switching power supply brick, feeds that into what looks like two DC-DC convertors which clean up the switching DC and turns it into +/-12V. Now my knowledge on DC-DC convertors is pretty limited, but I think because they switch at much higher frequencies than the laptop brick, it means the noise is inaudible to the ear. Also as the brick can be positioned away from the synth, the interference generated by it doesn't affect the synth.

At least I think that's the theory! As I say, my knowledge is limited so someone please stop me if I'm way off here!

My plan is to build something similar. I could just buy the Zeus, but it doesn't supply the +/-15V that I need, and the connectors aren't compatible with my DIY system so I'd end up modding it heavily.

My plan is to take a laptop PSU that outputs 18VDC and feed it to two DC-DC convertors that will output the +/-15VDC that I need.

I was thinking of using something like this to give me the +15VDC: http://uk.mouser.com/ProductDetail/Cincon/EC7B-24S15/?qs=sGAEpiMZZMtwaiKVUtQsNZk%2fyhBUJKktSIxQ6LwPsOs%3d

I can't seem to find much on the net about best practices when using these things. Do I literally just feed the DC-DC convertor +18VDC and I get +15VDC from the output? Do I need to filter the DC at all? I can't seem to find any application notes at all!

Would someone be able to point me in the right direction about using DC-DC convertors, and to let me know if my theory above sounds about right?

Thanks a lot!

 

[PRR]

> I can't seem to find any application notes at all!

There's not even a real datasheet linked from Mouser; to me, that's a non-starter.

There's a Trim which I might ignore, but what do I do about the Remote on/off?

> a laptop PSU that outputs 18VDC

18V is the very bottom of the listed input range. Are you sure it is enough? (A real datasheet would help.)

$44 is a startling price. (Also note there is no stock and 2.5 month lead time.)

The result seems to be +/-15V at 1.3 Amps. Or 40 Watts. In my mind, a 40W DC supply is probably NOT the heaviest lifting involved with taking a mod-synth out for gigs. Nothing compared to speakers or power-amps. If that's not your job, you still have mixer, stand, and the synth itself. The one I used to attend was BIG. If yours isn't, it probably "should be" for live gigs?

Since you can find 17V flaptop lumps for $5 on eBay, and an LDO regulator is $2, it could be sensible to get *two* power-lumps and two regulators, cobble-up the AC cords.

Or just drag the present DC supply. Don't mess with what works. Especially in live performance.

 

[letterbeacon]

Thanks for the reply!

I guess this is also about streamlining my synth. At the moment the case I bought is fairly deep to accomodate the two transformers and PSU PCBs etc. If I had something similar to the Zeus I linked to then I could build a much shallower case. You're right that messing with something that already works is probably a bad thing, but I'm jealous of the guys running commercial rigs (but on +/-12V) and are able to have nice shallow cases using switching power!! There must be something I can DIY!

The result seems to be +/-15V at 1.3 Amps. Or 40 Watts. In my mind, a 40W DC supply is probably NOT the heaviest lifting involved with taking a mod-synth out for gigs.

The plan would be to have a few of these DC-DC converters running from one large laptop power brick.

There's not even a real datasheet linked from Mouser; to me, that's a non-starter.

Maybe I picked the wrong DC-DC converter, and that's probably down to me having zero experience with them. I just can't find any info on application notes, or best practice when using them anywhere on the net! Are they really that simple that you can just plug power into them and that's it?

It seems like a few people here use DC-DC converters in their designs and I wondered if they have any tips on their practical usage...

 

[abbey road d enfer]

Currently I have two linear power supplies in my DIY modular synth. They work well and supply clean +/-15VDC to my system, but they are physically heavy. I'm looking at making my modular more portable for live performances and have started considering switching power supplies.

You could use these:
http://www.produktinfo.conrad.com/datenblaetter/500000-524999/511837-da-01-en-Dehner_SPS_G015_15_Netztm_get.pdf
I've used them to power a 51X 6-pack and am very pleased with their performance, particularly noise and heat dissipation. A very basic LC filter takes care of HF residual. It is tempting to be creative with salvation army parts but in the end you may find that it ends up as costly and less reliable...

 

[letterbeacon]

Great, thanks for that.

If I went for a higher powered model, would the noise increase at all?

 

[abbey road d enfer]

Great, thanks for that.

If I went for a higher powered model, would the noise increase at all?

Unfortunately I can only guess. ASSuming the larger ones are designed in accordance with the same rules as the smaller ones, noise should be nearly identical.