Design Article
Product How-To: 350W + 350W Class D power amp in the size of an iPod
Jun Honda, Yasushi Nishimura and Liwei Zheng
8/23/2011 1:44 PM EDT
Figure 3 is an example of a 2 channel 370W+370W Class D amplifier. This design features the IRF6775M DirectFET® from International Rectifier rated at 150V, 47m ohms, 25nC in a surface mountable package that enables small footprint while optimizing PCB layout.
Although power dissipation of a Class D amplifier is significantly smaller compared to its conventional Class AB counterpart, thermal design is still not a negligible part of the effort. Unlike Class AB, efficiency is a function of the MOSFET temperature. The higher die temperature increases RDS(ON) , thus conduction loss in the MOSFET. On the other hand, a good portion of the switching loss comes from reverse recovery charge Qrr in the body diode which has a positive temperature coefficient. Higher junction temperature increases overshoot/undershoot due to the higher Qrr.
The IRS2052M integrates all four essential functional blocks along with clock oscillator and thermal protection. A clean THD+Noise vs. output power waveform in Figure 4 indicates successful noise management in the controller IC.
Thanks to the low Qg in the MOSFET making gate drive easier, the control IC can also deal with a noise sensitive analog section on the same die. In addition, the low Qg in the MOSFET allows low gate drive power so that all four gate driver stages fit in a small MLP package.
The resulting design example is a 4" x 2.8" board space that offers a complete design in the size of an iPod at the efficiency of 90% while providing comparable audio performance to an equivalent output power Class AB amplifier. The latest Class D design brings higher audio quality with superior power efficiency at lower system cost which makes this topology achieve ever close to the ideal amplifier.
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Robotics Developer
8/25/2011 3:08 PM EDT
Very nice compact design! Is there a possible way to get the PCBs or a kit? Just wondering...
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studleylee
8/25/2011 7:14 PM EDT
https://ec.irf.com/v6/en/US/adirect/ir?cmd=catSearchFrame&domSendTo=byID&domProductQueryName=IRAUDAMP10
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studleylee
8/25/2011 7:04 PM EDT
I'm Salivating big time!!!!
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fdunn
8/25/2011 8:54 PM EDT
Love it!
So when is the author going to release it in kit form or fully assembled?
Also what is the max current for the +/- 50Vdc power supply and how much noise is allowed on these lines (ie: can a switchmode power supply be used?)
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turboeclipse
8/29/2011 3:07 PM EDT
This is a half-bridge design! What about power supply pumping issues at low frequencies? This could result in destruction of the power supply and amplifier.
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kendallcp
8/29/2011 3:19 PM EDT
"Class D topology is perfect in theory. It is free from non-linearity, meaning there is zero distortion"
Boy, these guys have got a big disappointment coming! The best switching amplifiers can perform well and sound great, but let's take it easy with the hyperbole.
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1Sparky
8/29/2011 7:27 PM EDT
Curious article, I see more work in Class D amps which seem to have never been mentioned in Audiophile circles(at least I only hear it in derision and casual glances)...My take on it is that the 'D' System will ultimately be less reliable than a comparable Class A system. You will need digital filtering and expensive power supply components, quite a bit more complex designs and similar high-priced devices...I am surprised the Japanese authors seem to be unaware of their forefathers' interest in Hi-Fi, as they made some really high quality gear in the 70's and 80's! The first statement gets me too...as cost was seldom an issue in the pursuit of premium sound in those days; 'trade-off' seldom entered the conversation! If I ever run across a 'stereo system' touting Class D innards, I'll be sure to have a careful listen.
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1Sparky
8/29/2011 7:37 PM EDT
btw, Radio and other kinds of tubes known as Audion, valve, Triode, etc. are patented by some and developed by others. Tesla deserves a mention in this circle and, in general, naming a device is sufficient as there is much uncertainty about the personalities behind 'ownership' of any technology.
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sime_attero
8/31/2011 8:22 AM EDT
1Sparky:
These IR Class-D modulators are closed loop, and as such can run quite happily on a basic (and cheap) unregulated power supply. The PSRR of this design is roughly comparable to other closed loop A and AB designs.
Power supply pumping is definitely a very real issue, and many half-bridge stereo amplifiers run the two channels out of phase and reverse the speaker output terminals on one channel to preserve absolute phase on both channels. Since power supply pumping tends to be a low-frequency, high amplitude issue, and low-frequency content in most program material is pretty "mono", this approach effectively eliminates any danger from power supply pumping.
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sinsinsin49
9/1/2011 2:53 AM EDT
I would like to see the +/-50V power supply for this amplifier "in the size of an(other) iPod". Where should I look?
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andigtech
9/1/2011 10:01 AM EDT
Well sinsinsin49 is right. The IR Class-D Audio Amp exists for quite some time but I never got a response from IR regarding a suitable SMPS. I was working on a DJ surface controller two years back and we intended to include an AMP right into the unit so that a portable party machine could be realized. But dropped it due to the SMPS issues. Also DC protection is important. Who wants $$$$ speakers to be fried !!!
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Tom.ChaklosJr.
9/16/2011 3:21 PM EDT
I went to IR's website and this Reference design is not yet being sold. But the other ones all cost about $300 each. Here is the link to thier ref design page.
http://www.irf.com/technical-info/refdesigns/audiokits.html
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