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Old 16th January 2008, 03:28 PM   #1
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Default Switch Mode Design.....help?

I'm working on making a gainclone (first Power amp project). I'm still in the works for optimizing my PCB layout. However I have arrived to the point of the project of which I was dreading the most, the power supply. I was going to go with the standard toroid transformer design, but those things are bulky, heavy, and expensive.

Backing up a bit, my father is big into VERY high end audio. He has (excuse me for not knowing the brand name) some VERY high end, VERY expensive 1kw mono block amps for his woofers. They are in a nice, neat, small package and look very slim line. I know they use a Switch mode power supply to keep heat, and form-factor down.

I guess the meaning of this post is, I would like to incorporate my own SWPS into my design. I know I can go out an buy pre-made kits, but wheres the DIY in that? Does anyone know where to find or even have schematics for a high power SMPS? Or know of any articles that could aid me in a design for a ~400-500watt SMPS? I found a few small articles (more like quick blurbs) that talk about it, and schematics for 30watt supplies, but this just isnt going to cut it. Now I'm not an EE by any means, so I cant really do much design beyond converting a schematic into PCB, so I guess "modifying" a schematic is just out of the question.

Thankyou for all help you guys/gals can provide me with!


David
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Old 16th January 2008, 03:44 PM   #2
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Forgive me for asking, but why so much power?
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Old 16th January 2008, 05:45 PM   #3
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Well this system is not going to be the cream of the crop high end audio. This is going to be a good system that will be used for a home theater and general music. I'm making a pair of line arrays that these amps will power. There is going to be x16 drivers per channel running 35watt continuous rated and 50watts max per driver. Also knowing my roommates, they have this issue with turning every amp in the house up to "11 " so I would like to have the amp big enough to handle it when it's needed, along with robust enough to handle large power outputs without releasing the "smoke within the ICs"
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Old 16th January 2008, 10:25 PM   #4
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Not to be snotty... but switchmode design is probably not the best starting point. Your own capabilities aside, just the equipment needed is considerable.

One of the biggest obstacles lies in designing and building the magnetic elements... it is difficult... even when you know what you are doing. Magnetic design also employs some amount of trial and error... gets expensive real quick.

If you hate power supplies... BUY some... and be a happy guy. Paint the resistor red and TELL people you built them.

If you insist on learning switchmode... start out with a buck convertor... then a flyback... then a forward... then a push pull. Start small... 5 or 10 watts... less smoke... smaller shrapnel... smaller injuries.

The fundamental book is: Switching Power Supply Design by Abraham Pressman.

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Old 30th January 2008, 08:07 PM   #5
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Forgive me for my ignorance on this, but I'm doing some research simply to get my head around it all. Chances are I'll still end up buying one pre-built, how-ever I would still like to understand the design and practical applications of a SMPS. In my research I've come across many different designs as poobah listed above. If I'm trying to convert a 120Vac to say 60-0-60 (or any other voltage under that), isolated, with the smallest form factor, which design would I should I go with?
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Old 30th January 2008, 08:13 PM   #6
poobah is offline poobah  United States
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Push Pull would generally give the smallest form.

Switchers are about copper & iron... a push pull uses the iron in both polarities.

Go to Linear Technologies and look at app note 19

Also... go to Onsemi and look for their SMPS stuff... this stuff is a pretty good tutorial.



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Old 30th January 2008, 08:34 PM   #7
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Thanks poobah, once again. I went to those sites, not sure what I was looking for. I tried searching both site using keywords but nothing came up that looked useful. You think you could help me out with a link? Or guide me on where to look?
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Old 30th January 2008, 08:37 PM   #8
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'ang on...

Here:

http://www.smps.us/

That should get you started... look toward the right.... "SMPS topologies"

One key to understanding SMPS is that caps store POTENTIAL energy... and inductors store KINETIC energy. Don't know how much physics you've learned.

Also... forget some of what you learned about transformers... learn to think of transformers as "COUPLED inductors"...

open book quiz Friday!

get readin'


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Old 31st January 2008, 01:07 PM   #9
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Ah thanks there poobah. I know think I know what you mean by coupled inductors (basically a 1:1 transformer? or is it used more like a flyback transformer?) In my research thus far, I see how you can get different voltage outputs with a DC source (used Spice models to understand more) but one thing I was always wondering is how they Isolate everything? I know you cant have a direct connection from the mains, it's just too dangerous. I just want to know how ever as a isolation transformer, how can you go from a 12lbs toroid to a small 1/2lbs inductor? I guess I just need to keep reading to find that answer!
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