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Old 15th March 2013, 04:57 AM   #21
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Originally Posted by Thunau View Post
So, would a Class A amplifier with its constant draw be a perfect candidate for a SPS?
Sort of. Unfortunately the constant load means some of the advantages of being able to optimize the feedback/compensation network for a specific load pole placement go unused. And the overall efficiency is still low 'cause, hey, it's class A. Helpful for line regulation, though, and the constant load makes passive filtering of switching noise quite a bit easier.

In the watt or so range I've found class AB with a linear supply tends to end up equally or slightly more efficient. A 2.5+W class A amp off a buck converter would be a nice little project. Another class A application where switching works well is tube heaters.

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Originally Posted by Osvaldo de Banfield View Post
I have the project in paper, and haven't scanner, but with time I can draw in LTS or Express Schematic.
Looking forward to seeing it when you have the chance. Substituting a digital camera for a scanner might work.
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Old 15th March 2013, 05:22 AM   #22
JMFahey is offline JMFahey  Argentina
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If you pm lorylaci he has the original copy.
Mine has been bodged to suit my mosfets and transformer core.

A 27951 thread is here:
IRS27951 / IRS27952
OK, thanks a lot.
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Old 15th March 2013, 05:50 AM   #23
kimbo is offline kimbo  Australia
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Nelson uses them in his Amp Camp Class A amp.

Amp Camp Amp #1

As he says..... 'What? An audiophile component with a switching power supply? Get over it it works fine.'
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Old 15th March 2013, 08:34 AM   #24
marce is offline marce  United Kingdom
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Outside of the Audio (exclude pro audio) amps, SMPS's are used everywhere, both large and small on board supplies for various digital voltages. They are used almost exclusivly over linear because not only are they cheaper but more efficient and these days that is a concern when power consuption is a design consideration.
Nice to see Mr Pass using them, it may help dispell the myths that abound regarding SMPS supplies.
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Old 15th March 2013, 09:15 AM   #25
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Originally Posted by JMFahey View Post


"Uncommon" as in *all* PCs, *all* cellphone chargers, *all* TVs , *all* CD/*DVD players , *all* monitors, etc?
Well, besides the 5 to 10 SMPS present in every household, yes, *maybe* they could be considered somewhat uncommon
Hi ! title changed to be more specific
Regards,
gino
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Old 15th March 2013, 09:27 AM   #26
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Hello ! if I understand well SPS have difficulties when the current draw is variable
It is really interesting that they can be good for class A amps
Small power high quality amps with high efficiency speakers ... interesting
Thanks to all for the very valuable informations.
Kind regards,
gino
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Old 15th March 2013, 01:30 PM   #27
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Originally Posted by ginetto61 View Post
Hello ! if I understand well SPS have difficulties when the current draw is variable
It is really interesting that they can be good for class A amps
Small power high quality amps with high efficiency speakers ... interesting
Thanks to all for the very valuable informations.
Kind regards,
gino
It depends of the topology choice. Flyback naturally has the largest dynamic range and then fast to response upon load variations, and all buck derived are the worse, because the large low pass filter at its output generates large time delay in the regulation feedback loop. I repaired lots of SMPS, and flyback's can support large overloads, and a range of 100:1 of load transients are well supported by them, but it also depends on loop characteristics.
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Old 15th March 2013, 01:58 PM   #28
marce is offline marce  United Kingdom
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Quote:
Hello ! if I understand well SPS have difficulties when the current draw is variable
It is really interesting that they can be good for class A amps
Small power high quality amps with high efficiency speakers ... interesting
Thanks to all for the very valuable informations.
Kind regards,
Yes and no, today you can design multiphase SMPS's so each phase runs at optimum load, and you switch phases on or off to go with the load requirements, add spread spectrum to the design and you can get some interesting supplies, that are efficient over a wide range and have minimal noise, done 2 to 8 phase layouts recently.
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Old 15th March 2013, 02:35 PM   #29
jcx is online now jcx  United States
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spread spectrum PS – could be considered a stupid trick to game a bureaucratic limit

get the real EMI power down for real quality, minimal effect on associated equipment

then spread spectrum should be evaluated in the system context – whether a (hopefully weak) spectral peak causes more problems in the system than a lower level, broad spectrum – that may excite circuit resonances that the narrower line could be designed to avoid

in general good ground up sw mode ps design is considerably more complicated than most diy audio linear amps


it is suprizing that we have gotten away so long with exemption/non-enforcement of line harmonic limits in consumer audio with linear supplies

Last edited by jcx; 15th March 2013 at 02:37 PM.
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Old 15th March 2013, 04:13 PM   #30
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Originally Posted by Osvaldo de Banfield View Post
I repaired lots of SMPS, and flyback's can support large overloads, and a range of 100:1 of load transients are well supported by them, but it also depends on loop characteristics.
100:1 is a bit marginal for class AB but workable if the phase margin can be tuned to be good at the low end of the load range and acceptable at the high end (class D might be a little easier due to the quiescent dissipation often being a bit higher). I wouldn't mind having another look.

Any suggestions on a design approach that would work with off the shelf magnetics? Or for low cost, low minimum order custom magnetics? The ones I've plugged audio design requirements into all come back with application specific windings, which seems to mean one has to buy a couple hundred US dollars/euros of sample run magnetics to do a hello world on the supply. Even if the design's good out of the gate, no tweaking is needed, and one finds buyers for the unused parts that kind of kills the cost structure of a typical DIY project where you're going to build one or two supplies (I don't actually listen to the living room rig all that much so when I worked it out the cost riser for custom magnetics to supply the small amps I use was enough to pay the power bill on a linear supply implementation for the better part of a decade).

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Originally Posted by marce View Post
Yes and no, today you can design multiphase SMPS's so each phase runs at optimum load, and you switch phases on or off to go with the load requirements
Challenge is switching the phases on and off fast and cleanly enough to track the current demand without startup or shutdown transients bonking the rails. This is essentially the class H amp problem, just with current tracking rather than voltage tracking. Performance with real time tracking is usually not so hot, with the usual fix being to lag the audio signal to give the supply some lead time to get to where it needs to be. Fine for audio playback, can be problematic for video, and the variability of music signals can clobber the efficiency gains. For example, if you have a small class AB amp that goes between 10mA quiescent and around 1A peak the optimal multiphase implementation is nominally a 10-100mA phase and a 100mA-1A phase. Home listening levels tend to peak right around that 100mA breakpoint, with the result being both phases end up wanting to always be on.

A maybe more viable approach---depending on personal listening levels, speaker efficiencies, and so on---would be a composite chip amp with a two phase supply. Those are usually around 30mA quiescent so one could have a 30-300mA phase and a 300-3 to 4A phase that would go up to the chip amp's current limit (these numbers are for two phases per channel but one could have higher current phases serving more channels). I've toyed with this idea but never found an implementation I was exited about enough to want to build. A linear supply with the control loop regulated and the output devices unregulated provides the same sort of scaling at lower cost since the incremental cost of increasing the size of the output devices' heat sink is usually pretty low. One concept I keep coming back to is amps with a loud mode. Idea is you flip a switch and control circuitry boosts the supply output and increases the amp's gain for, say, a 20dB increase in output power. This aligns with a two phase SMPS but, similarly, I've never found an implementation elegant enough to be worth building.
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