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Class D Switching Power Amplifiers and Power D/A conversion

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Old 8th November 2011, 04:52 AM   #11
ssanmor is offline ssanmor  Spain
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Quote:
glad to see you answering in a friendly and technical manner.
It couldn't be other way, you haven't been unrespectful, only that your judgement has been a bit hasty.

Anyway, Class-I (which is stated in all our datasheets with proper earthing recommendations) is not a problem in practice, I wouldn't expect 400W+ PSUs (SPS80 is even capable of >1200W continuous, >2000W music, despite the official rating) to be Class-II (double insulation), only small consumer applications. Any professional amplifier requires earth and we do support our customers so they wire and install the PSUs properly. Ground loops are usually not a problem if everything's done correctly.
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Old 8th November 2011, 05:09 AM   #12
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Quote:
Originally Posted by JohnsonAV View Post
Hey everyone,

This is my first post here, so go easy on me. I'm putting together two Class D Audio SDS-258's, what would be an appropriate power supply for such a combination? I spoke with Tom and he recommended +-65V, 8-10A. Any recommendations? I'm not looking to build one.

Thanks.

Aaron
I'm using 2 SMPS800R from Connex. Very happy with them.

I think I have read elsewhere that Class D Audio have recommended the SMPS800R ?

That amp has the balanced input? I'd be interested to hear how it works out for you as I'm looking for a balanced input amp for my subwoofers.
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Old 8th November 2011, 05:17 PM   #13
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Hi Cristi,
I am finding 1.4mm between the drain plates of the primary switches and the screw.
Between primary caps and secondary resistors I am finding 1.3mm.
The insulating sleeves of e-caps are generally not considered as protective insulation.
It is not obvious whether the transformer offers 6.6mm creepage or not.
No, I am not planning to unwind and debug it - at least not for free.
I need my spare time to go on with my class D, that's why I decided to purchase a SMPS from stock instead of designing one.
If I have to design a smps, I am asking for money.
If I have to design a classD amp I go for it with a smile.
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Old 8th November 2011, 05:27 PM   #14
ssanmor is offline ssanmor  Spain
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No, definitely screwing the power mosfets to a heatsink using metal screws is not a good idea, you will have small clearances as Chocoholic shows. Unless you use dedicated heatsink for each mosfet with proper clearances, although that's generally impractical for moderate to high power levels.
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Old 8th November 2011, 05:51 PM   #15
AP2 is offline AP2  Italy
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Hi,
I think it is right to look at the building, if they have complied with the standards for insulation. EN etc.
But I see that no one observes the behavior of the SMPS, given that supply power to an amplifier, if the output is clean (especially for class D), or if you have a good response time (if it is a regulated SMPS).

Regards
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Old 8th November 2011, 06:22 PM   #16
Pafi is offline Pafi  Hungary
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Originally Posted by ChocoHolic View Post
Hi Cristi,
I am finding 1.4mm between the drain plates of the primary switches and the screw.
Yes, but it is not a free surface, it's covered by an elastic insulator. Even if there were a very small gap, contamination is not likely to penetrate into there. So I wouldn't say it's really risky.

Quote:
Between primary caps and secondary resistors I am finding 1.3mm. The insulating sleeves of e-caps are generally not considered as protective insulation.
Indeed, it's not enough by itself, but as long as it's intact, it's perfectly enough against creepage, furthermore with the other insulator layers (resistor+air) they fulfill the double/enforced insulation requirement also. (IMHO!)
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Old 8th November 2011, 06:31 PM   #17
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I bought this smps, because of regulation and multiple postings of Cristi, which made me trust in his expertise. And I still do, even when I am not happy with that smps in particular.
I did not check for the regulation, because I decided not to use it.

And regarding regulation I must state that the hypex is not regulated.
When loaded it sags and shows pretty some 100Hz output ripple.
HF-ripple appears to be far less than the 100Hz ripple.
Thanks to sync rectifiers the 100Hz ripple is symmetrical on pos and neg rail also at unsymmetric load. And also it perfectly avoids supply rail pumping.
Regulated +/- 12V outputs are just done by 7805 and 7905, resulting in the known noise of multiple hundrets of nV/sqrt(Hz).
==> Not really something special, but a good fit for my planned amp.

Edit: Did I say 7805 and 7905? Rubbish. 7812 and 7912 of course.

In general I agree to AP2 that regulation behavior can be pretty important.
The regulation time constants (or even regulation overshoot/ringing) can easily happen to be in the audible frequency range. If such artifacts happen in that range + the sagging/overshoot/ringing is not really small, then it might become necessary to evaluate the audiophile suitability in detail.

Last edited by ChocoHolic; 8th November 2011 at 06:45 PM.
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Old 8th November 2011, 06:44 PM   #18
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Hi Pafi,
I am a old fashioned German engineer and consequently cannot handle standards in a relaxed and souvereign way...
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Old 8th November 2011, 07:29 PM   #19
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Quote:
Originally Posted by Pafi View Post
Yes, but it is not a free surface, it's covered by an elastic insulator. Even if there were a very small gap, contamination is not likely to penetrate into there. So I wouldn't say it's really risky.
Well, real physics seem to be country depending in this regard.

When looking to UL world, then any kind of potting is accepted to reduce the required creepages (as long as the potting is flame retardant )
I am willing to agree that the compressed silicone isolation will do a similar good job.

When looking to Europe safety relevant pottings have to be vacuum pottings and the evaluation of potting is done by cutting the potted thing into thin slices. If any bulbs are found inside ==> rejection.

In fact I am not sure which philosophy is closer to reality.
If we look to really high voltages the european bubble panic appears well reasoned for me. If you have stacked dielectrica the electric field splits inverse to dieletric constant. Most pottings/plastic isolator with dielectric constants between 2-6. Means by far higher than air. Consequently inside enclosed air bubbles there will happen undesired high fields, which in turn could lead to partial discharges...
But if we look to our concerned mains voltages of 230V (or 120V) and multiple mm distances, then we are far away from such effects.
Hm.. Currents creeping on a surface (or betweenface ), between two isolators closely pressed together? Anybody out there looking for a Phd topic ?


Quote:
Originally Posted by Pafi View Post
Indeed, it's not enough by itself, but as long as it's intact, it's perfectly enough against creepage, furthermore with the other insulator layers (resistor+air) they fulfill the double/enforced insulation requirement also.(IMHO!)
At this point I am definitely not on your side.
Neither the insulating sleeve of the e-caps, nor the resistor coating is considered as safety relevant insulation.
...can't get out of my German skin...
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Old 8th November 2011, 09:25 PM   #20
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Originally Posted by ssanmor View Post
..screwing the power mosfets to a heatsink using metal screws is not a good idea...
Plastic / Vinyl screws would also not help much here.
Creepage would increase just by the thickness of the insulation washer. The trouble starts as soon as you have a hole/interruption in the washer close to the drain plate or any other conductive part of the MosFet.

And looking to the insulation washer:
For basic insulation there is no requirement for the thickness.
But for double/reinforced insulation the EN60065 requires a minimum material thickness of 0.4mm. Ohps,...did I check the hypex design for this? No, I didn't .
May be - I'd better stop to check what I buy and start believing instead.
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