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Old 26th June 2017, 04:30 PM   #11
cdsgames is offline cdsgames  Canada
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you need 5V/3A

PMP4478 AC in, 5V 3A Quasi-resonant Flyback Converter with Optimized Light Load Efficiency Reference Design | TI.com
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Old 26th June 2017, 05:59 PM   #12
dmills is offline dmills  United Kingdom
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Quote:
It all adds up doesn't it ?
First design the SYSTEM, including calculating what the performance requirements are for each subsystem, then pick the subsystems based on those requirements, this is good design.

The 'Best' is not a meaningful requirement. 100uV RMS noise over DC to 20MHz (The usual measurement bandwidth for most power supply datasheets), between 20 and 100% load, is a possible requirement. Common mode noise currents less then 1mA over DC-20MHz is a possible requirement. Greater then 50ms hold up at 100% load is a possible requirement, MBTF > 100KHrs at 100% load, 60C ambient is a possible requirement, maybe smaller then 8 cubic inches is a possible requirement....

Seriously, 1uV in an uncommonly narrow bandwidth? When powering a high speed processor supplied by the cheapest on board buck converters possible? Who cares? It is not like that noise contribution is even going to be visible in the roar of non synchronised spread spectrum clocks and bucks on the CPU card.

Now if you are designing either a precision clock or small signal analogue then you care, but you start from a completely different place, LC filters and low noise linear regulators having PSRR up to above where the LC filter cuts off, then you start worrying about the grounding, signal integrity and (sometimes) screening, but first you get your matlab on to see how good you need to make things, only once you have the numbers do you start shopping.

Then you LISTEN, and Measure, and LISTEN some more, and have your friends around and LISTEN doubly blind, and measure some more... One thing I quickly realised was that if I could hear it, I could measure it, but that correlating what sounds good to what measures what is a difficult problem, still good design will usually tell, and good design is NOT automatically the use of the most expensive possible parts.

Sometimes you can get sneaky, I did an ADC/Mic preamp design powered by a switcher, I locked the switcher to a harmonic of the word clock so that any switching noise that got into the analogue section would alias to DC and be removed by the digital filters. It effectively made the leakage from the switcher pretty much a non issue, I mean it was 100dB down anyway, but when I fitted that jumper and the loop locked you literally could not see it in the output any more.

ZVS quasi resonant converters are generally MUCH cleaner then bucks or flyback converters, but even they can be tamed if you are smart about it (Cheap ~60W flybacks are often bad news at ~25MHz or so due to the reverse recovery charge and transformer parasitics, this seems to be worse on the class VI efficiency ones, I assume due to less snubber).

I would recommend that anyone building stuff get a few books on RF design, you cannot get away from it these days, and certainly anyone using logic faster then the 4000 series or doing ADC/DAC based things needs to think in terms of RF not audio.

Regards, Dan.
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Old 28th June 2017, 07:33 AM   #13
cdsgames is offline cdsgames  Canada
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SO basically we have 2 choices..ZVS quasi resonant or just plain quasi resonant. The ZVS is a more expensive/bigger design and quasi resonant is cheaper and smaller

On the design that I proposed, first thing will be to add a RC snubber on the bridge rectifier. It will reduce the noise radiated in mains and smooth further the DC
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Old 28th June 2017, 12:05 PM   #14
dmills is offline dmills  United Kingdom
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Originally Posted by cdsgames View Post
The ZVS is a more expensive/bigger design and quasi resonant is cheaper and smaller
About right, depends on how much efficiency matters at high load for your application.

The efficiency advantage of ZVS only really becomes apparent once the savings in cooling start to matter (Usually cooling is the elephant in the room where efficiency is concerned rather then the direct energy cost), I use them in radio transmitters but usually pick something simpler for most audio doings.

Actually if you are smart about your design and layout, even a good quality flyback can be fine, you just need to design based on what you know it will do.

Regards, Dan.
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Old 28th June 2017, 12:11 PM   #15
cdsgames is offline cdsgames  Canada
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Efficiency does not matter much at 15W. We want low noise in mains and of course low noise on the output.
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Old 6th July 2017, 10:54 AM   #16
cdsgames is offline cdsgames  Canada
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Design has started with some improvements to the schematic. First thing we did...on each diode we have a RC snubber to reduce the oscillation.
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Old 10th July 2017, 11:11 AM   #17
cdsgames is offline cdsgames  Canada
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Oscillations observed on mosfet and diodes. We will use RC snubbers to tame them.
Attached Files
File Type: pdf 5vout1vperdiv.compressed.pdf (108.0 KB, 156 views)
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Old 11th July 2017, 07:19 AM   #18
soundcheck is offline soundcheck  Germany
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Great to see that you guys (@Allo) are working on a PS product. I hope this time a single voltage (e.g. 5V) device.

Some things to keep in mind:

1. Don't forget that the "numerous" cable parameters matter big time This plus the right choice of plugs might have ten times more impact than your observed oscillations.

2. A good balance of risetime plus current delivery has to be found Overregulation, overdamping/-filtering, high ESR, low buffer capacity might be some of the things to eliminate as much as possible. I fought this by adding low ESR buffer capacity to the iFi. 3. I'm not sure if a flexible DC cable length wouldn't have been a better approach on the iFi. Fixed length and then rather long DC cables are not what I'd call the ultimate solution.

4. And the other thing which IMO might not be the best of all approaches is to have the supply sitting right in the mains distribution block. I'd rather see it closer to the device.

5. iFi IMO has done a great job by supplying several uselful adapters. Something you want to think of if you intend to be commercially successful.

Just my thoughts (based on my experiences).

Looking forward to an iPower alternative.

Good luck.

Last edited by soundcheck; 11th July 2017 at 07:26 AM.
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Old 11th July 2017, 09:20 AM   #19
cdsgames is offline cdsgames  Canada
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Hi

1. Are you referring to better cables (like wire thickness ?)
2. Already taken care of... I am sure you will like what we did :-)
3. Not enough space on our casing.. if you referring to retractable cables.
4. Agreed. Taken care of.
5. Included..I am thinking if a specif material (like cooper) will be better than standard.
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Old 11th July 2017, 11:42 AM   #20
soundcheck is offline soundcheck  Germany
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"Better cables"

Obviously that's a topic on its own. iFi uses coax + ferrite bead. There are some advantages by using coax. Decades ago Thorsten Loesch - the man behind the iPower - wrote an article on TNT about interconnects. He applies pretty much the same principles for the iPower DC cable nowadays.

There are probably better choices. But the coax might be a good (or the best) compromise. However. The "targeted" retail price will probably dictate your choice. If you go for a rather cheap and/or rather inflexible solution, I'd appreciate if you'd keep the DC outlet DIY friendly. Meaning: I should be able to rather easily open the case and attach (even soldering is OK ) my own custom cable!

Cheers

Last edited by soundcheck; 11th July 2017 at 11:47 AM.
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