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 Class D Switching Power Amplifiers and Power D/A conversion

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 7th February 2005, 03:58 PM #31 richie00boy   Did it Himself diyAudio Member     Join Date: Nov 2003 Location: Gloucestershire, England, UK I thought from my post of #23 in this thread you would have got it into your head that I am not simply doubling power arbitrarily. It's not to take account 'in case of' lower loads or anything like that -- it is simply the minimum requirement to drive your desired power into your desired load and no lower, with sinewaves, without burning up. If you read that post again you will see why the transformer has to have an AC voltage that is 0.707 x DC plus a bit, that I trust is simple and obvious. The reason that DC current is multiplied by 1.61 is that is the current capacity required from the AC side when pulling through a bridge rectifier is increased by this factor. This is simple, fundamental bridge rectifier theory! Thank you __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, modules and more.
classd4sure
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Join Date: Feb 2004
Quote:
 Originally posted by richie00boy I thought from my post of #23 in this thread you would have got it into your head that I am not simply doubling power arbitrarily. It's not to take account 'in case of' lower loads or anything like that -- it is simply the minimum requirement to drive your desired power into your desired load and no lower, with sinewaves, without burning up. If you read that post again you will see why the transformer has to have an AC voltage that is 0.707 x DC plus a bit, that I trust is simple and obvious. The reason that DC current is multiplied by 1.61 is that is the current capacity required from the AC side when pulling through a bridge rectifier is increased by this factor. This is simple, fundamental bridge rectifier theory! Thank you
I didn't ask you why you used 45V, if you read my post again, you'll see that simply and obviously. I would say 45V is likely on the high side though, conducting mosfets won't even drop 1 volt.

I'll also point out this is an incorrect way of calculating rails for a UCD which has voltage protection, and for which good design requires one to account for a 10% mains overvoltage condition, as well as the transformer's regulation factor.

Post #23 isn't arbitrary, but a mindless doubling is. You can absorb that much can't you? Maybe if you can't, try comming down from your high horse, it could help.

If it is simple fundamental bridge rectifier theory you're using then you should know it's 1.8. Not a single rectifier version uses 1.61.

You're apparently incapable of an intelligent exchange, perhaps your blood sugar is low? You seem cranky. Go have a biscuit.

Thank you.

richie00boy
Did it Himself
diyAudio Member

Join Date: Nov 2003
Location: Gloucestershire, England, UK
Oh come on, let's not let this flare up again

Quote:
 Originally posted by classd4sure I didn't ask you why you used 45V, if you read my post again, you'll see that simply and obviously. I would say 45V is likely on the high side though, conducting mosfets won't even drop 1 volt.
Conducting MOSFETs will drop a little and unless they have a gate driver that can rise above the +ve rail they will drop more than a volt or two. I'm guessing that the UcD will have sufficiently sophisticated drive circuitry to overcome this and thus the bulk of the losses will be through the rectifier diodes. So for a 400W UcD you are looking at a required AC voltage of about 45V. I think we are reasonably in agreement with that.

Quote:
 Originally posted by classd4sure I'll also point out this is an incorrect way of calculating rails for a UCD which has voltage protection, and for which good design requires one to account for a 10% mains overvoltage condition, as well as the transformer's regulation factor.
I agree that for a good design we should take line and transformer regulation into account. However, if we do this it puts up the AC voltage requirement (and hence VA) even more to maintain that 400W output at worst case. And I cannot see what relevance any overvoltage protection an amp may have has in this part of the calculations.

Quote:
 Originally posted by classd4sure Post #23 isn't arbitrary, but a mindless doubling is. You can absorb that much can't you? Maybe if you can't, try comming down from your high horse, it could help.
But my whole point was that it appeared to me that I was being accused of mindlessly doubling the speaker power to arrive at the transformer VA. Maybe I was wrong

Quote:
 Originally posted by classd4sure If it is simple fundamental bridge rectifier theory you're using then you should know it's 1.8. Not a single rectifier version uses 1.61.
This is the best bit 1.8 is more than 1.61, which makes the VA add up to even more. That 800VA transformer of yours is now looking rather weedy to drive your 2x 400W amp. This is irrelevant anyway as (and I await your apology ) once you have read a basics text book or searched the net you will see that it is in fact multiply by 1.61 or divide by 0.62 (same result). Remember we are talking about full-wave, bridge rectified AC.

Quote:
 Originally posted by classd4sure You're apparently incapable of an intelligent exchange, perhaps your blood sugar is low? You seem cranky. Go have a biscuit. Thank you.
My exchange has been intelligent, I'm the one showing all my working and providing formulas, rather than, umm...

Sound of jammy dodgers packet being opened
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classd4sure
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Join Date: Feb 2004
Quote:
 Oh come on, let's not let this flare up again
Sorry, I've an admittedly weak tolerance for concentrated condescension, like poison it can only be taken in small doses.

Anyway I'm really not here, or trying, to argue, just to learn and help where I can. I do appreciate that your recent post has a much better tone, and so I respond accordingly.

Quote:
 I agree that for a good design we should take line and transformer regulation into account. However, if we do this it puts up the AC voltage requirement (and hence VA) even more to maintain that 400W output at worst case. And I cannot see what relevance any overvoltage protection an amp may have has in this part of the calculations.
Here I fail to understand, you know, thick head and all. The UCD has protection that shuts it down at a certain voltage, used to be 63 volts, now it's higher and a non issue, but this math was done before that, so what the hey. Let's assume a regulation factor of 5%, along with the 10% mains over voltage. We have to allow for a 15% overshoot worst case, without tripping the protection. So realistically we wound up with less voltage, because 56.6 * 1.15 = 65.09 and the amp has cut out 2 volts ago. So then to maintain VA, we'd want more current, but it will never get used because we can't fight ohms law. In reality, what we have isn't exactly a 400W amp. This has been fixed though so it's no longer a problem. That's the relevance to the over voltage protection as I see it. In truth it is no longer relevant with the higher protection level.

Quote:
 But my whole point was that it appeared to me that I was being accused of mindlessly doubling the speaker power to arrive at the transformer VA. Maybe I was wrong
No not at all. I simply wanted to know more about it, which is why I asked originally. I fail to see why you couldn't have explained it without being so condescending. You had a decent answer which left me with another question, apparently you saw that as more accusations, I dont' work that way, I'm fairly straight forward.

Quote:
 This is the best bit I await your apology once you have read a basics text book or searched the net. Remember we are talking about full-wave, bridge rectified AC.
I see more condescension and at this point, the smilie ain't smoothin it over.

http://www.atc-frost.com/products/design/va.htm

http://www.plitron.com/pages/technote.htm

have a scroll down to "Rectifier Circuits"

Apology denied. Besides I don't really care, I was just being combative at this point.

Quote:
 Sound of jammy dodgers packet being opened
I'm glad that amused you, it was meant to.

All the same, it's time I took my leave.

Cheerio, ol chap.

richie00boy
Did it Himself
diyAudio Member

Join Date: Nov 2003
Location: Gloucestershire, England, UK
I now see how you were concerned about the overvoltage protection of the UcD400. A very valid concern to those expecting to get 400W out of the amp. I wonder if they have increased the voltage on the amps as well, but's that's not for this thread

I must admit to never having seen the 1.8 factor in over 10 years of electronics, it's always been 1.61. However, those links you posted are valid sources. I can only assume that they are accounting for slightly higher peak currents and/or slightly longer conduction times for the rectifier diodes.

Quote:
 Originally posted by classd4sure Apology denied. Besides I don't really care, I was just being combative at this point.
You were doing so well, winning me round, until you dropped that clanger

I think we've covered the bases on this topic anyhow, and anybody should be able to pick up the methodology, reasoning and formulas to design a PSU for a UcD or ZAPpulse amp easily enough from this thread
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 8th February 2005, 09:59 AM #36 destroyer X   diyAudio Member     Join Date: Feb 2004 Location: Recife - Brasil Northeast My 45 years of experience, are in garbage can now... terrible feeling! I can understand why you are discussing that matter so deep, and those things will are confused to me too, as i am completely crazy with things happening here, at my home. I bougth a very good audio system (sorry, not rich) from Phillips, and its power consumption (written in the back panel) is 125 watts... so i expect to have something around 96 watts power...but as specifications are "manipulated"..... "tricky informs"....i will acept 60 watts of sound....and this is perfect in my mind.... very nice power....because those 45 years, i could realize that normal (not hard to move) speakers, goes to limit movement with 4 or 5 volts.....and the heavier ones need 10 to 15 volts...so.....30 watts is OK!....each channel, perfect! The main problem are specifications...they informed us, power as their top maximum, short time....not even continuous seems to be.... specifications talk in 10 percent distortion....and that distortion is enormous...sounds terrible, it is not more sound, it turns noise!..... and when you go searching, you will find a very small power...i could see 12 watts to a 120 watts amplifier in some Philips Class D chip....and they are making those crazy things with us....mine, with 125 watts consumption, is rated to 200 + 200 watts (they did not tell us what kind of "watts" are those). This is impossible....125 watts consumption producing more power than consumption....creating energy! So i connected multimeters....in AC range...good to 60 hertz bass....those instruments can measure with less than 10 percent error, and having some continuous tone, we can avoid problems related to pointer weigth...i tried digital too..... could measure 7 volts over 4 ohms...and, increasing volume, could reach 20 volts, but distortion was a hell, as i use external hi level drive signal, and beeing square waves, measurements loose precision, as turns almost alike continuous. So, for the good old days ...this amplifier can produce 12 watts each channel, clean watts.... can produce some square crazy wave of much more power. But this is not what happens hearing....that crazy thing sounds alike 100 watts each channel.... and give a punch in bass enormous...and kicked all my amplifier's s without too much effort, not only in quality of watts produced, as in quantity of watts produced. So...i cannot understand?....what is going on? Can i respect those calculations you are discussing to have some idea of the power produced? I am a hell confused.... those watts i cannot measure with multimeter!!!! HELP!!! regards, Carlos __________________ Dx Sonic signature https://www.youtube.com/watch?v=4EPR8i3IJeE; New VW; https://www.youtube.com/watch?v=v3jrrEkQUXw
destroyer X
diyAudio Member

Join Date: Feb 2004
Location: Recife - Brasil Northeast
The equipment is heavy...have enormous transformer; 3 X 3 X 3 inches

This size makes me believe in much more than 400 watts.

regards,

Carlos
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destroyer X
diyAudio Member

Join Date: Feb 2004
Location: Recife - Brasil Northeast
Near future i will open it to have internal pictures too.

One more image.

Carlos
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 12aa.jpg (54.6 KB, 221 views)

destroyer X
diyAudio Member

Join Date: Feb 2004
Location: Recife - Brasil Northeast
The last image, to present you, the equipment i am talking about.

This way, things turns more real.

Carlos
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 15aa.jpg (41.4 KB, 210 views)

 8th February 2005, 10:23 AM #40 richie00boy   Did it Himself diyAudio Member     Join Date: Nov 2003 Location: Gloucestershire, England, UK Carlos, Thank you for your contribution I assume you are using a 'known' same set of speakers for your tests, i.e. the same speakers for each amplifier? The key thing about rating a transformer is the acceptable tempearture rise for a given power draw. Your 'boom box' will likely be rated to give out high short term power, but cannot sustain this continuously without overheating the transformer, and the supply begins to collapse after not very long. In contrast, your 'hifi' amplifier will likely have a power supply that cannot match the same short term power as the 'boom box', but it can give out sustained power. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, modules and more.

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