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Old 27th December 2011, 02:20 AM   #1
Mrbobb is offline Mrbobb  United States
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Default Discuss: Modern Highly Efficient PSUs

So starting with Apple's portable devices, I have noticed in the last few years the portables' wall plugs have REALLY SHRUNKED! Now your iPhone's wall plug is but an oversized dice giving you a full AMP of power, a few years before that you were looking at a weighty cube containing an old fashioned iron transformer+bridge rectifier+470uF electrolitic. Not only that, the new plugs run COOL! because obviously they are more efficient and loose less of the energy in heat. I have also noticed the new generic wall plugs they sell now, i.e.: Radio Shack are smaller AND with higher ratings and have an Efficiency Rating label.

Obviously I missed the boat on what transpired recently, *somebody* made a discovery, an invention that made this possible. In the 80's when I was going to electronics school, I remembered the teacher saying back then: PS are innefficient! the most you can get out of them was like 35% efficiency, 65% energy loss!

So anybody want to chime in what I missed?
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Old 27th December 2011, 03:21 AM   #2
kevinkr is offline kevinkr  United States
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Compact, cheap line operated switching supplies.
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
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Old 27th December 2011, 03:46 AM   #3
wwenze is offline wwenze  Singapore
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The *some* discovery was made as early as... ...actually I dunno when SMPS was invented but it has been used for high-power applications since I was born that's for sure.

Four things - the requirement for high efficiency and low vampire power draw, the reduction in price of integrated circuits, the advancements in metal processing, and the sharp rise in copper prices. For a long time low-wattage supplies have been sticking to linear since the economic of scale for SMPS only kicks in at higher wattages. Then SMPS became cheaper than linear for 20-30W and found their way into DVD players and etc. Then now <10W supplies are also SMPS.

For us UK-standard users, the iPhone's power adapter isn't even an oversized dice.

Click the image to open in full size.

Last edited by wwenze; 27th December 2011 at 03:51 AM.
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Old 27th December 2011, 04:40 AM   #4
benb is offline benb  United States
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I remember the 5V 1A "wallwarts" for I think it was the Commodore 64 (bargain priced at $5 at Delta Electronics, an Atlanta surplus outfit that eventually converted to selling computers), weighed a pound or two and you could use it for a hammer (except it was in plastic case). I bought a cheap flipcam a few years ago, its charger is as small and light as any old-fashioned transformer-operated 5V 50mA wallwart, and it's rated at 5V 1A. It appears cellphone makers have finally standardized on these chargers with the mini USB connector, so people won't be throwing away old chargers when they get a new phone with an incompatible charging port. Here's one surplus cheap, $1.49 but it's only 1/2 amp (!):
SALE! - Lightweight Mini USB Charger for: Cell Phones, MP3 P-The Electronic Goldmine

Yes, it's new line-operated switching regulator chips. I think I've seen such a chip by National, I suppose I could look up a few part numbers if you wanted to see.

The main thing inefficient about line-transformer power supplies are the transformer. Larger power supplies using transformers are I think substantially higher than the figure you gave, perhaps 50 to 70 percent, and the transformer only got "warm" instead of "hot." Smaller 50/60Hz transformers as used in older wallwarts are really bad though, and 35 percent might be an optimistic figure. I read something about their design about a decade ago, they often saturate the core as a crude method of voltage regulation.

But back to SMPS, they're good for efficiency (80 to 90 percent, or even higher as you go to higher power), often good for power factor (whereas linears never have been, as rectifiers only conduct for a small portion of the cycle), everything seems great, but ...

The downfall for audio is SMPS's make lots of electrical noise. This can be filtered somewhat, but at the frequencies they operate, 100kHz and up, they can radiate as well as conduct hash and switching noise through their output power connections. It would seem these frequencies are beyond audibility and wouldn't be a problem, but switching supplies can sometimes oscillate with subharmonics of the operating frequency, and these can be within the audio band. The only audio app these are actually "good" for is powering huge 1000+ watt PA systems where efficiency and low power factor are more important than pristine sound quality, and getting as much output power as you can out of a 120V 20A circuit.

I don't know that Apple started SMPS wallwarts, I'm guessing the parts for these tiny off-line switchers became cheaper than tiny 50/60Hz transformers about ten years ago, and that marked the end of the 60Hz transformer as a high-volume mass-produced item. Even at the height of their manufacture such transformers were expensive, and they've always been heavy, adding to product shipping costs.
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Old 28th December 2011, 04:59 AM   #5
! is offline !  United States
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One difference is everything is made disposable these days. So long as you didn't exceed their current rating, the old unregulated linear supplies would last for a couple decades or longer. You can crack open a 40 year old wall wart and solder in a new 50 cent capacitor in under 5 minutes and have it work for another two decades.

Today's little SMPS packs tend to last somewhere between end of warranty and 3 years continuous use at the current rating, maybe a bit longer if the casing is vented and it uses non-electrolytic capacitors. The tiny ones are acceptable to consumers because they're more portable and because they are meant for limited # of VA hours output over the product warranty period. IOW, you aren't powering your iPhone at full power 24 hours a day/7 days a week from one.

They can be built more durable and long lasting but that is not a popular line item feature to marketing departments and it would come as extra expense consumers wouldn't consider enough (would be ignorant of) to spend more money on.
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Old 28th December 2011, 07:23 AM   #6
dtproff is offline dtproff  United States
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I am a power supply engineer that helped on some of these shrink their size and make higher efficiency designs. We always knew how to do them but knowone would spend the few extra cents it cost to hit the higher efficiencies and smaller form factors. To be honest, because of the commodity prices the BOM costs are actually lower now than 5 years ago. It forced us to rethink the standard magnetics approach (now a lot of the cores are custom) and thin the plastics while paying more attention to EMI in an effort to shrink the BOM cost.

Right now in the 65W-240W adapter range (non-air cooled) the top end for density without a cost premium is about 14W/in^3.

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Old 28th December 2011, 08:32 PM   #7
Mrbobb is offline Mrbobb  United States
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Originally Posted by benb View Post
I don't know that Apple started SMPS wallwarts
Don't know for sure, but I would not hesitate giving Steve Jobs one more accolate, the way he's with thinness and perfection.

I recently looked at an Apple TV, that dang tiny box does alot AND has a built-in PSU which to me is absolutely amazing. U buy anything else, and it comes with an ugly wallwart.
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