SMPS for Class D....resonant or not? - diyAudio
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Old 1st January 2012, 10:32 AM   #1
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Default SMPS for Class D....resonant or not?

Hello,

I notice that a number of off-the-shelf SMPS's for audio usage are LLC resonant type. They have no PFC.

IMHO, there are problems with this, because LLC resonant converters are are known for not having good line regulation......as the following explains under the "frequency and gain" section


Using quasi-resonant and resonant converters

Not only that, but LLC resonant converters are in voltage mode, and this is not going to be as good with transient response as current mode controlled SMPS's.
...Also, an LLC resonant converter has a transient response which depends on its frequency of operation.......at switching frequencies near the upper resonant frequency, the transient response of an LLC resonant converter is best.......but as you go above this frequency, the transient response gets markedly poorer.

...the problem with this is that when the input voltage is variable, then that means that the LLC converter's switching frequency will at times NOT be near its upper resonant frequency, and so its transient response will not be too good.


So i believe that this is why coldamp.com have chosen *not* to use a resonant converter for their SMPS.......SPS30...............

https://www.coldamp.com/store/sps30.html

.....you can see the output inductors which proove that this is not an LLC resonant converter......and i believe that they have chosen the non-resonant direction because of the above reasons that i have stated.

Though it would be superb if owners of LLC resonant supplies could come forward and confirm the above.
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Old 1st January 2012, 03:50 PM   #2
Cristi is offline Cristi  Europe
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I believe that this article was so fascinating that you refuse to read further articles which might say that there is still possible to achieve good regulation, sometimes even better that of a hard-switched power supply.
i've already posted some transient response results in one of the countless threads which you opened regarding some LLC converters issues.
personally i designed the LLC power supplies to provide output voltage regulation while the mains input voltage is is within 95-130V or 193-256V. more or less is useless, first, because 99% of the ppls which use them live in a decent place and they can afford relatively good quality power (min-max voltage limits, frequency, wave shape, harmonics) and second, if the mains voltage would drop below 95 or 193V or increase over 130V or 256V i believe they will have other reason of concern than the output voltage stability of the SMPS500R.

I understand my reasons and others designers reasons which choose LLC topology instead of old, poorly efficient and highly EMI polluting hard switching topology, but i cannot understand why would someone prefer to use hard switched flyback or forward instead. yes, you will remind me once again that is current mode, has fast transient response, etc. but the same can be achieved with a well designed soft-switched converter, not necessarily LLC. build one, test it and come back and tell us what did you found.

Off-topic: I never liked shrimps, in fact i hated shrimps until i eat it first time. now i try to eat less because of high fat content.
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Old 3rd January 2012, 01:16 PM   #3
ssanmor is offline ssanmor  Spain
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Thanks for the comparison and thoughts.
Coldamp has selected modified hard-switching topology because of several reasons, mainly reliability and well controlled switching frequency (that allows things such as well controlled, easy filtered noise frequency and synchronization with Class-D amplifiers in order to reduce potential whistles or noises that can be produced with other kinds of switching PSUs). BTW, this is the same reason why we decided to make our amplifiers constant-frequency instead of self-oscillating.

The theoretical higher EMI of hard-switching (not so a problem with careful design) has been improved in our case with spread spectrum modulation technique, that reduces EMI peaks considerably.
However, even before spread-spectrum was introduced, I must say that we found no practical problem when operating several of our PSUs together at full continuous power near sensitive electronics.
Efficiency is extremely high, as well, well above 95%
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Old 3rd January 2012, 01:42 PM   #4
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Quote:
Originally Posted by ssanmor View Post
Thanks for the comparison and thoughts.
Coldamp has selected modified hard-switching topology because of several reasons, mainly reliability and well controlled switching frequency (that allows things such as well controlled, easy filtered noise frequency and synchronization with Class-D amplifiers in order to reduce potential whistles or noises that can be produced with other kinds of switching PSUs). BTW, this is the same reason why we decided to make our amplifiers constant-frequency instead of self-oscillating.

The theoretical higher EMI of hard-switching (not so a problem with careful design) has been improved in our case with spread spectrum modulation technique, that reduces EMI peaks considerably.
However, even before spread-spectrum was introduced, I must say that we found no practical problem when operating several of our PSUs together at full continuous power near sensitive electronics.
Efficiency is extremely high, as well, well above 95%
it would be interesting to see some mesurments of EMI / Ripple of SMPS output.

I noticed, that no one show such information's, for some reason.

Thank you
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Old 4th January 2012, 11:56 AM   #5
ssanmor is offline ssanmor  Spain
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We are working on that, to provide a serious measurement report soon.
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