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Class D Amplifier Design

Authored on: Jan 3, 2011 by Hugo Letourneau

Technical Paper / Application Note

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True audiophile electronic designers have always dreamed of designing the perfect amplifier perfectly reproducing the recorded soundstage. They may have started to dream about it when they learned in their first electronic classes, that the class-A topology gives exceptional results in terms of linearity. The main advantage of Class D topology is its efficiency that can get in the high nineties of percents due to its digital nature. Read this application note to learn more about Class D Audio Amplifier Design.
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musiklab Posted Mar 9, 2011

When reading a paper it is unfortunate that EE times finds it convenient to take up a sizeable proportion of the page with inane advertising or stationary banners left and right of the reading pane, so a reader must scroll up and down, left and right to read a paper- this quickly detracts from the reading effort and prevents me from casually browsing around- too much Chaff. Give me back my screen, and respect that I spend my time here, please.

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Jerry.Brittingham Posted Mar 16, 2011

Amen

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zeeglen Posted Mar 16, 2011

Overall an interesting paper, other than minor graphical errors in Figs 1 and 2 which are obvious and ignorable. As for the advertisements, these are what make EE Times online free for readers. The publication staff of EE Times cannot work for free. The advertisements are necessary if you want to continue subscribing to a free and informative publication. If you do not like the ads, you are free to avoid coming here. One of the ads was for EE Times moderator. Hmmm....maybe I will apply...

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Xyber Posted Mar 23, 2011

LOL, Your comments are rather difficult to read because of the amount of advertising squeezing them... ;-)

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Medina0 Posted Mar 23, 2011

The painful reality of the advertisements is that they pay for the publishing of the paper. I guess they are a necessary evil.

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David Ashton Posted Mar 30, 2011

Hey, guys, don't be lazy...one click (on the PDF icon at the top (or where it says Click to Download) and you have an almost fullscreen copy of the paper without that many ads. Save the PDF and reopen it and you have one with NO ads. Even with my slow (256K) broadband it doesn't take toooo long. As Zeeglen says, the advertising enables you to get this stuff free. Plus the "Navigate to Related Information" bar often leads to more gems. Just be grateful EETimes gives you such easy access to this info, all in one place. When I started 30+ years ago, you depended on magazines once a month and Databooks which were expensive and difficult to get. EETimes is a veritable paradise by comparison.

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atarifan49 Posted Jun 17, 2014

Thanks for the tip. The stupid VIEW button doesn't work. It does get frustrating to have to view documents on this website because most of the time the connection just hangs and can never get it to come up - I guest that is why I don't bother opening them!

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ADKngc Posted Mar 30, 2011

What about the 10.8 Megabytes containing a 2 page presentation? Any idea why this is the case?

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johnmoran Posted Apr 25, 2013

It's because they don't know how to use a pdf writer properly. This paper is effectively saved as a big image, rather than text. You usually get this problem when the big important paper writer offloads the encoding into pdf to the poor office lacky. I suspect they (the lacky) do this on purpose to get their own back! Kind regards - John

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MichelCharest Posted Mar 26, 2011

The solution to have the best sounding amplifier with the highest efficiency would be to have a topology that combines a class A and a class D. Many of you probably believe it is impossible but this technology exists. It is called ADH for Analog Digital Hybrid and it was developed by a couple of engineers that used to work for Nortel France. They took four years to refine their design and then started, 2 years ago, a company called Devialet. They are selling an amplifier that is able to push out 2 times 240W but only consumes 20W on idle. The envelope of the signal is generated by a small class A amplifier that provides only 1% of the total power and the remainder of the power is supplied by a class D current source that is slaved to the class A.

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Fabio007 Posted Apr 3, 2011

I have just checked out the patent for this (US7,545,212) and my comment is: this has been done before. The key idea is that a voltage-follower transistor (part of the voltage amplifier) is protected form variations of Vce by a cascoding transistor. The current in that cascoding transistor is small, since the current supplied to the output state is augmented by a current source fed to the common junction of the cacsoding and cascoded transistors (if there are such words!). Said current source just happens to be a switcher (a buck converter) hence high-efficiency results. I would claim that making a current source from a switching transistor and an inductor (a buck-converter) and having its current controlled from a signal that represents another current, is certainly not new, and neither is using that current source to "augment" the output of a "current-source". Further, having this basically supply the bulk of the output current of an audio amplifiers has also been done before. Unless I am missing something that is very subtle...

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GordonScott Posted Jun 23, 2011

Indeed. I often wonder how on earth some patents get granted. Ive been using digital supplies controlled exactly like that for high(ish) power analogue amplification for years, partly because in my context the amplification has to be effectively class A to function and I need to keep the dissipation as low as I can or fry the circuits. Cascode Vce buffering in the voltage gain stage of an audio amplifier is ususual, but by no means unheard of. Doug Self discusses the technique in his audio power amplifiers book. What they're patenting of course, is the particular combination of these things in that context. In my case the voltage gain is just an op-amp as I only need distortion below 1%.

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Fabio007 Posted Jul 21, 2011

Hello Gordon, yes, agreed, some patents really are laughable and would fail any test of "novelty" or "prior art". Just want to raise a point re: cascoding the output pass transistor in a class AB (or class A, B, or C) audio amplifier. Yes this is unusual (at least for "non-audiophile" amplifiers), but prior art goes back at least to the late 70s with Nelson Pass and his "Stasis" amplifier, refer US Patent 4,107,619, filed 20-Dec-1977. That patent covers using cascoding transistors to limit Vce variation on the final output transistors. The other idea of augmenting the output current of a linear amplifier with a switcher-based current source is also not new, refer US Patent 4,516,080 filed 30-Mar-1983, in particular fig 10. The combination of these two ideas, well I don't have a patent for that just at hand, but if these two previous patents dated late 70s and early 80s, then I'm sure that not long after these patents were granted then the idea of applying these two concepts to the same amplifier would have occurred to someone...! Maybe you have an example at hand? ...And I am not claiming that these two patents are the earliest examples of "prior art" one can find; for example, the class-D concept for audio amplifiers can be dated back to the 1940s...! I'll post the Patent no later...cheers.

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ADKngc Posted Mar 30, 2011

First I love PDF but I don't understand why the PDF on class-D's is 10 Megabytes but only 2 pages. I have had 50 page illustrated books in PDF format come through using only 5 megabytes. What Am I missing something? Second item, I suggest those who have a snooty attitude about advertisement pony up for a donation to the magazine. Advertising pays the bills.

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Akegarasu Posted Nov 23, 2011

The file volume is so huge, and it takes too long in down loading...

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Kuttichira Posted Jan 6, 2012

Well the files are being stored in high quality version of pdf resulting in a heavy file. Suggest that the files be saved for standard quality which will be smaller in size.

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ibm221 Posted Dec 14, 2011

Eversince I used my email address to register as a EET member (to be able to post here). EET is the WORST spam source I ever seen. they also keep on changing their email address so I can't block them. all this reminds me of cockroachs...

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cutedaddy Posted Sep 24, 2014

Check Hypex Ncore 400 class D amp. The work is done. And i mean ALL the work. More fidelity than any existing design of any description.

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