Where to find Switching PSU tutorials?

[ejbasses]

After building countless PSUs for people using your usual traffo, I want to learn how to build those switching PSUs like the onespots and poweralls. is there a place in the net where i can find information on how to build these things?

[loscha]

Best place to look is the data sheets for the switching chips themselves.
They have pages of data, and lots of pretty equations for you to put your numbers into.

[Paul Perry (Frostwave)]

Linear Technology are really the leading switcher designers. Their app notes rock.
Note, though, an efficient design requires a lot of work. The key is the inductor...

Plenty of info on the net, for an intro try http://www.hills2.u-net.com/electron/smps.htm

[George Giblet]

Let me give you some friendly advice.  Don't try to build a mains powered switchmode from scratch if you aren't a professional (even a pro wouldn't do a  DIY PSU, it's not worth the trouble). You can kill yourself, you can kill other people, you can cause fires and it is likely you will exceed radiated and conducted emissions standards.  These things aren't thrown together there's a lot of fine details behind the scenes.  Also it will cost you more money to get the high frequency transformers, inductors and capacitors than it would to buy a prebuilt unit and you won't get a nice molded case.  If you find these effects orientated units too expensive buy a generic regulated PSU based on switch mode technology - it will be better than anyone's first attempt at making one.

If you just want to understand switch modes check out applications notes from manufactures like national semiconductors, linear technology, texas instruments.  There's an massive amount of information on this stuff - do a google.  Most of this stuff is the *bare basics*.  Some of the  ST microelectronics notes give you some hints at designing transformers and snubbers but again they only touch on the subject.

Godlyke Powerall:

http://www.godlyke.com/product.asp?item=102

Visual Sound One Spot:

http://www.visualsound.net/1spot.htm

[R.G.]

Let me add an enthusiastic round of support for George's warning. I am (or was) a switching power supply pro. I did that for a living for years.

(1) It's dangerous. You need to work with live wall-socket AC on your prototypes. There are ways to do this, but they require expen$ive equipment and generally a buddy working with you to turn things off before you fry.
(2) It's expensive. The equipment necessary just to test what you've done is enough to buy a lifetime supply of power supplies off the shelf. Beyond that, what do you put the finished unit into? A Hammond box? A Raco box? The boxes are custom designed, and there's a whole layer of mechanical complication to that.
(3) Last and least, it's complicated. The layouts are CRITICAL, the magnetics are custom, and you need to have your result tested for RF emissions so you don't shut down all the electronics near you.

If you just want to learn how, great! Go google. But trying to save money on these is false economy. I know for a fact that te 1Spot is available in the low $20 range. You can't get an oscilloscope that will see the switching speeds you need to look at in a design for fifty times that.

[Paul Perry (Frostwave)]

I cetainly agree with GG & RG!
But, there is (maybe) a place for switch mode in stompboxes.. not from the mains (that is, as people have said, a quick way to kill or injure youself, eg. by components just exploding in front of what were your eyes), but by making supplies that convert say 6v lead acid  gel cell batteries to regulated +-9v supplies. The DIY led torch guys do this kind of stuff, they have a lot in common with us.

[R.G.]

Yeah, I'll go for that. doing low voltage DC to DC switchers is attainable for home guys.

However, this is not something you can do blind, at least not very well, so there's still a steep price for equipment to be able to tell what you're doing. A 60Mhz delayed sweep scope is about the minimum, and storage helps tremendously. My old Tek 7633 drives me nuts because it's old and not ... quite good enough for that stuff any more. I'd like to spring for a new DSO, but I don't have the bucks for the moment.

[Paul Perry (Frostwave)]

Switch mode power supply design is about the only time that you really need a twin beam (as opposed to a mere twin trace) scope. Good luck finding one of those babies.....

[Gripp]

While almost staying on topic...

I'm interested in these switching DC/DC converters http://www.elfa.se/elfa-bin/dyndok.pl?lang=en&vat=0&dok=2017305.htm, http://www.elfa.se/pdf/69/06956007.pdf.

This seems to be a way to avoid having someone make me a custom wound toroid and still get many isolated 9V outputs in a small package. Although not cheep, all other ways seem to get even more expensive here in Sweden.

What worries me is the max capacitive load of 33µF. Would a basic buffer do or perhaps a linear regulator after, other ideas?
As I understand it, switching supplies needs to be loaded down by a small amount to work properly, any practical consequences of this , other than loading it enough in the simplest possible way?
Or should I quickly forget about this whole thing?

Best!
/Pelle G

[Paul Perry (Frostwave)]

I presume the maximum capacitive loading is designed to limit the maximum current flowing to the cap when the unit is first switched on. If that is the case, then maybe a problem will occur if you run the unit straight to a FX with a lot of cap across the power rails, regardless of whether you have a regulator or buffer in the way.
As to the question of switchers needing a permanent load..... it depends on the design, some do, and some don't. I havn't looked at the specs of the unit in question.

[Gripp]

Thanks Paul!

I presume the maximum capacitive loading is designed to limit the maximum current flowing to the cap when the unit is first switched on. If that is the case, then maybe a problem will occur if you run the unit straight to a FX with a lot of cap across the power rails, regardless of whether you have a regulator or buffer in the way.

Yes, that makes perfect sense. Hmmm, and of course, my power-hungry fx have a lot of cap across the rails... (in excess of 33µF anyway, 100µF is not uncommon)

I guess I'll have to try one and see if it can cope with running outside the spec.

Edit: Just read the datasheet for the Nth time and saw that they at least were short circuit protected for 1s max.

[Paul Perry (Frostwave)]

Maybe the capacitance on the output has some influence on the stability of the feedback loop that is comparing the output voltage with an internal reference. If might well be, that havign an 'excessive' capacitance on it makes it go unstable. Even a 'simple' linear three pin regulator, can have 'issues' with certain capacitance values on the output. (treated in the National Semi application notes 30 years ago).