| Rhesusminus |
How high efficiency is possible with class D. I saw a sales brochure claiming 97% efficiency in a range of 100W - 500W Public Address amplifiers. I have designed both class D amps and switching power supplies, and my first reaction was that this was a load of hogwash.
Is it at all possible to achieve this kind of efficiency in an amplifier?
I mean, I would have to struggle hard to achieve this kind of efficiency in any kind of power supply! |
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| IVX |
| i've at moment 97% H-bridge 400VDC 100KHz 300W, but after replacing the poor IRF mosfets to new ST, i'll wait >98% and at 600-700w. So even 99% for low frequence switching and for half bridge isn't impossible.:cool: |
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| fredos |
I reach it, but you should use APT or IXYS fast and low RDSon mosfet, with low lose rectifier, etc....Impossible to reach with ''commercial'' mosfet, you have to move to industrial parts.
Fredos
www.d-amp.com |
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| Pafi |
| quote: | | Is it at all possible to achieve this kind of efficiency in an amplifier? |
Fredos can reach at least 100%. :D
In a complete amplifier (power connector->filter->rectifier->PFC->DC/AC->trafo->rectifier->choke,capacitor->bridge->filter, plus fan, modulator, signal processor circuitry, etc...) I can't believe such efficiency. In the power modul, it's OK.
| quote: | | i've at moment 97% H-bridge 400VDC 100KHz 300W, but after replacing the poor IRF mosfets to new ST, i'll wait >98% and at 600-700w. So even 99% |
What kind of amplifier is this? (400V 0,8A?)
Be careful! 3% loss or 1% loss is a huge difference! Don't underestimate the power of switching loss! :-) (Unless you use ZVS) |
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| soongsc |
| quote: | Originally posted by Pafi
Fredos can reach at least 100%. :D
In a complete amplifier (power connector->filter->rectifier->PFC->DC/AC->trafo->rectifier->choke,capacitor->bridge->filter, plus fan, modulator, signal processor circuitry, etc...) I can't believe such efficiency. In the power modul, it's OK.
What kind of amplifier is this? (400V 0,8A?)
Be careful! 3% loss or 1% loss is a huge difference! Don't underestimate the power of switching loss! :-) (Unless you use ZVS) |
There's a thread "Free Energy Devices" that shows a device said to generate more energy given it. :D |
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| IVX |
| fredos, why only APT or IXYZ? Infineon presented month ago 500v 130mOhm 48nC, not so bad thing. BTW, how to obtain samples from Infineon? |
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| BWRX |
| quote: | Originally posted by IVX
BTW, how to obtain samples from Infineon? |
You have to know somebody on the inside ;) |
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| fredos |
290nC...Total gate charge...Nothing impressive, specialy the 120ns turn-off...Far from APT or IXYS!
Fredos |
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| FastEddy |
IVX / BWRX: " ... BTW, how to obtain samples from Infineon? ..."
Infineon buys stuff, they never sell stuff. Check out their web site = filled with "carreer opportunities" and new supplier information ... meaning they are in expansion mode. Their customers appear to be big companies with long term projects ... or race tracks and car shows. (As Forbes.com would say: "short the stock.")
:confused: |
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| FastEddy |
Class-D is a new breed of cat. Just as flouresent bulbs are more efficient than incandecent bulbs, "switching" pulse width modulation amps are more efficient than "brute force" or current dump amps (type A or AB). The over all thermal efficiencies tells the true nature of Class-D, being as they deliver most of the power to the load instead of consuming a significant amount of power as heat. The number being bandied about for "efficiency" of Class-D are generally erronious. The numbers to look for for comparison should be thermal efficiencies. Modern motor speed control using pulse width modulation is significantly more thermally efficient than simple variable resistance control (same, same w/ Class-D) ... that's why the EPA & the EU want to see more of 'em = less heat generated = more environmentally correct = less power consumed for the job.
Put your hand on Class-A or Class-A/B amp heat sinks after several hours of continuous operation :hot: ... then try the same with a Class-D amp of the same power, relatively same heat sinks == :cool:
A well designed pulse width modulation amp (Class-D) should have thermal efficiencies greater than 85% or more ... over all thermal efficiency ... from power plug to speaker terminals.
(Also that 6.3 volt filiment in a vacuum tube is called a heater .. for good reason ... )
The true tests should be the specs like THD ... and the listening experience, not the efficiencies. Unless you want sodium vapor lighting in your living room, there is still no substitute for an incandecent bulb to read by IMOP.
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| IVX |
| quote: | Originally posted by fredos
290nC...Total gate charge...Nothing impressive, specialy the 120ns turn-off...Far from APT or IXYS!
Fredos |
what you mean? I told about IPP50R140 500v 130mOm(typ) 48nC(<<<290nC!). |
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| Spasticteapot |
I've got a 95% efficient amplifier handy.
It's an H-bridge used to drive a ginormous motor.
Hey, you never said it had to be able to produce frequencies above 20hz! |
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| Pafi |
Fredos talks about efficiency measurement:
| quote: | | No PFC on amplifier, just measure power and effiency with real VA, not watts.. |
No comment... |
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| fredos |
The IPP50R140C3 was only 23A....Not enought for fews KW switching power supply!
Fredos |
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| fokker |
| quote: | Originally posted by fredos
I reach it, but you should use APT or IXYS fast and low RDSon mosfet, with low lose rectifier, etc....Impossible to reach with ''commercial'' mosfet, you have to move to industrial parts.
Fredos
www.d-amp.com |
what is a "commercial" mosfet vs. an "industrial" mosfet? |
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| BWRX |
Easy - a commercial mosfet is one used in commercial products while an industrial mosfet is one used in industrial products ;)
Seriously, he's mainly talking about devices used for different power levels. "commercial" devices being the ones used in "lower" power applications and "industrial" devices being the ones used in "higher" power applications. |
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| fredos |
What I call a commercial mosfet is something like Fairchild, IRF, MOSPEC, Infineon, low power series of ST. A fews $ mosfet in other word. What I call Industrial mosfet is APT, IXYS, big ST mosfet, a mosfet that you can push to 150% of it capacity without fear of faillure! But maybe 10 time the price of an commercial mosfet!
Fredos |
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| Eva |
There are really interesting Infineon parts readily available through Farnell in Europe, like a 600V 34A MOSFET with ultrafast body diode, 0.1 ohm typ. Rds-on and 163nC typ. total gate charge. Not to mention that this is the one I'm using in the last version of my +/-200V +/-35A LF class-D amplifier (with great success BTW).
On the other hand, after browsing several dozen datasheets, I was unable to find any device worth even trying from IXYS or APT. I can almost guarantee that at least all the MOSFET stuff from those manufacturers available through Farnell is useless and extremely expensive. Am I missing something or what? |
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| IVX |
| fredos, topic is "Record efficiency", but not "Record output power", however, 23A at 400VDC H-bridge give several KW, obviously. I guess, tales like this -"really cool can be APT/IXYS ONLY", actually just a popular myth. Commercial IPP50R140C3 from Infineon, outperforms any of the comparable APT "COOLMOS", IXYS will offer pretty good mosfet soon, but at moment many interesting specs is "tbd" (see http://ixdev.ixys.com/DataSheet/f7f...22b16bbb606.pdf). Maybe "commercial"/"industrial" just a cost ratio? |
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| Eva |
| quote: | Originally posted by fredos
What I call a commercial mosfet is something like Fairchild, IRF, MOSPEC, Infineon, low power series of ST. A fews $ mosfet in other word. What I call Industrial mosfet is APT, IXYS, big ST mosfet, a mosfet that you can push to 150% of it capacity without fear of faillure! But maybe 10 time the price of an commercial mosfet!
Fredos |
How do you manage to push MOSFET dissipation (or even drain current) 150% above rated while still keeping 99% efficiency? I may be missing something again...
I don't mind at all whether my switching MOSFETs or IGBTs are rated at 75W like low cost TO-220 parts or at 500W dissipation like ultra-expensive IXYS and APT stuff. They are rarely subject to more than 25W in my circuits. |
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| fredos |
Hello Eva
What I mean by this is that I dont push it to 150%, but means that you can push it more close to their limit without the risk of explosion!
I have lot of years of experience in class d and reliability on the field is really important. Lot of user use amplifier in stupid ways (that's the need for stupid proof protection and Mosfet). A cheap 13A IXYS mosfet can be abuse a lot more than a 23A IRF mosfet. That's what I have experiment with the time... And much better, most of the time are more efficient!
That's the breaking point I think between cheap and good products... It's not only if it do the job, but if it can do the job in any environement! Like on a gas generator, on african electricity network, or under tropical rain with 100% humidity when the show must go on! All this event will cause ''commercial'' mosfet to be overdrive, when overdrived ''industrial'' mosfet with electricity spike or humidity leak between drain and gate still work, bad, but still work without faillure! And no, I dont told you to test your amplifier under water.... But certification required a 8 hours test into 40 degree at 95% humidity....Poor Infineon, fairchild and IRF!
That's why, even with the price, I prefered IXYS and APT!
Reliability and effiency are my first concern!
Fredos |
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| Eva |
Hi Fredos
I may be still missing something...
The +/-200V +/-30A amplifier that I mentioned in one of my previous posts is currently being subject to the kind of certification tests that you have mentioned. The own customer is performing these tests as they are quite demanding people. Temperature and humidity conditions are likely to be as you mentioned. Output power is probably 1800W continuous and test periods are likely to be one week long rather than 8 hours.
I'm using Infineon MOSFETs (my favourite for 600V applications), Fairchild IGBTs, On Semiconductor diodes and IR drivers... No failures reported so far. Oh, and the entire amplifier including active PFC power supply is efficient enough to use a single convection-cooled heatsink, without fans. There is only a small fan to move some air inside the case to cool the magnetics and the resistors of the snubbers, and I'm doing my best to get rid of it (because the class-D switching stage itself and the PFC can produce 3KW continous if the magnetics don't overheat).
Furthermore, the previous prototype (no PFC) was also subject to the same endurance tests without failures, and it employed 12 low-cost 600V 10A TO-220 Infineon IGBTs to achieve over 1800W continuous output. However, the customer complained about 88% efficiency and 0.6 power factor, so I had to find a way to get into the 95% range including additional losses from an active PFC stage (it gave me lots of headaches!!)
I suppose that the difference is that some people is skilled enough to get big performance and reliability from small transistors while others just aren't (and will probably never be). |
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| fredos |
For space purpose, it's better with only 2 outputs...12 is too much for my case size! Anyways, you agree with me that 12 small outputs can be as reliable as 2 big one! And faillure are more probable with 12 outputs than 2! And I'm pretty sure that 12 of your outputs cost near the same as my 2 beast! So topology for topology, I think that we get the same result? No?
About PFC, their is no rule yet here, so I take the train when is there!
Fredos |
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| Eva |
There are reasons other than size or cost to use 12 small co-pack IGBTs with diode in a 400V full bridge rather than 4 big MOSFETs, you may discover some day...
BTW: Big TO-247, TO-218 and TO-3P cases exhibit quite poor performance in fast switching applications because lead inductance (in the 20nH range) resonates with internal drain-source and collector-emitter capacitance, usually in the 10Mhz to 50Mhz range. Lead inductance also imposes a limit on the switching slopes achievable with conventional gate drive circuits. An extra source or emitter lead with its own bonding wire attached to the die would be a great thing. The problem becomes even worse in those big "beast" devices due to increased capacitances and the higher currents being usually conducted. |
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| IVX |
| quote: | Originally posted by Eva
.. some people is skilled enough to get big performance and reliability from small transistors while others just aren't (and will probably never be). [/B] |
:drink: again hard, but EXACTLY :drink: |
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| fredos |
I dont call 62.5Khz fast switching....Ans most of the time, there is more inductance in the routing of PCB...Specialy with multiple outputs!
Fredos |
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| Eva |
To Fredos
It's really hard to discuss switching electronics with you because you seem to get most of the concepts wrong during most of the time. Switching speed is not necessarily related to frequency. You can sonsider my amplifier as an example of that, since everything is clocked at 48Khz (the PFC is synchronized ) but my turn-on crossover times from 400V to 0V are in the 60ns range and turn-off from 0V to 600V takes 25ns at full load. My switching at 48Khz is probably way faster than yours at 300Khz, and note that my turn-on is intentionally slowed down to reduce EMI and to avoid TO-247 self-resonance, because the magnetic snubbers that I use to limit diode di/dt cause very little current to be yet flowing after 60ns.
I'm taking advantage of more tricks to boost efficiency, but I can't reveal them for obvious reasons. I think that 95% full load efficiencty for an amplifieir including power supply can be considered state of the art. |
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| fokker |
| quote: | Originally posted by fredos
What I call a commercial mosfet is something like Fairchild, IRF, MOSPEC, Infineon, low power series of ST. A fews $ mosfet in other word. What I call Industrial mosfet is APT, IXYS, big ST mosfet, a mosfet that you can push to 150% of it capacity without fear of faillure! But maybe 10 time the price of an commercial mosfet!
Fredos |
sounds like to you the separation point is either price (more expensive = industrial) or failure tolerance (over "capacity" without failure?).
I can hardly see the 1st point: there are expensive devices from all manufacturers and what's the point?
on your second point: there is a difference between rated capacity and true capacity. a device manufacturer may decide to rate a part, for example, at 300v when in fact most of them can take 350v. I don't think logically it is possible to push one over its (true) capacity - that's just violates the definition of capacity.
a prudent design is one where a device isn't pushed over its (rated) capacity. But if you really want to, maybe you should just pick a higher rated part to beging with. |
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| Genomerics |
| quote: | Originally posted by Eva
I'm taking advantage of more tricks to boost efficiency, but I can't reveal them for obvious reasons. I think that 95% full load efficiencty for an amplifieir including power supply can be considered state of the art. |
IGBT turn Off
DNA |
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| Eva |
| quote: | | Not much more to say really. It appears to work although you might be worried about the reverse bias ratings of an IGBT. I liked it so much I went and filed a provisional UK patent, 04/11/06, on it. Not one of my best efforts so it's probably worthless. However, if you want a look then you can download it.... |
Genomerics approach, which he is trying to patent without having even bothered to try with real components, is clearly based in the following thread that I started two weeks before he filed the provisional patent. On the other hand, my thread shows real oscilloscope captures from a commercial power supply designed by me.
http://www.diyaudio.com/forums/show...&threadid=88740
Fortunately, the approach that I employed (no schematic shown) exhibits superior performance and does not require a coupled inductor. However, I will be no longer publishing any more of my 'tricks' in this forum. I'm sorry for all the DIYers, but I can't risk having more unfair cheaters trying to patent my work without having even bothered to heat their soldering irons... |
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| Pafi |
| quote: | | is clearly based in the following thread that I started two weeks before |
OK, probably it is based on it, but I don't see any problem with this! His conclusion and solution is quite different.
Let him to be happy with that! I think your soultion is better (due to its simplicity), but his one can work too. |
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| Jaka Racman |
| quote: | | However, I will be no longer publishing any more of my 'tricks' in this forum. I'm sorry for all the DIYers, but I can't risk having more unfair cheaters trying to patent my work without having even bothered to heat their soldering irons... |
It is high time that somebody tells you that all your "tricks" you post here are nothing more than reinventing hot water. And that is a compliment, since otherwise one might think that you purposely steal and post other's ideas to a bunch of class D amateurs. In the very same thread you have shown is a link to a previous implementation of what you claim to be "your" idea. Sweet Jesus, do you think you invented switchmode design? Next time you post something "original" just check it was not invented and described 20 years ago. Oh, let me guess you can't, you have no access to IEEE articles and you are to cheap to pay for a membership. Please do not bother replying, this is my last post here. This forum has deteriorated low enough. |
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| Genomerics |
| quote: | Originally posted by Eva
Genomerics approach, which he is trying to patent without having even bothered to try with real components, is clearly based in the following thread that I started two weeks before he filed the provisional patent. On the other hand, my thread shows real oscilloscope captures from a commercial power supply designed by me.
http://www.diyaudio.com/forums/show...&threadid=88740
Fortunately, the approach that I employed (no schematic shown) exhibits superior performance and does not require a coupled inductor. However, I will be no longer publishing any more of my 'tricks' in this forum. I'm sorry for all the DIYers, but I can't risk having more unfair cheaters trying to patent my work without having even bothered to heat their soldering irons... |
Honest Eva. I haven't tried to rip off one of your ideas. I hadn't seen your previous posting but I know you are doing this sort of stuff so I thought you might be interested.
I am playing with PFC, as you say just theoretically, and was having problems with power losses in mosfets so turned to IGBTs. I've looked at them before but never really liked them because of the switching losses.
This time I was forced to look harder and I did try paralleling the IGBT with a mosfet to achieve zero current turn off. Unfortunately it did not work, in simulation, for me so I guessed about stored charge and came up with the reverse bias/charge removal idea that is shown on the web page.
I did a patent search to see if there was something similar about and found things like....
paralleled IGBT/Mosfet1
paralleled IGBT/Mosfet2
But nothing that mentioned applying a reverse bias to the CE terminals to remove stored charge so I went and put a patent in. It's not a very good one and I doubt if anything will come of it which is why I published the web page.
Like I say I gave you the link because I know you are working on similar stuff and might be interested. I really did come up with the idea independantly. If you have something that works for you and it is simpler then that's great but please believe me.....
I'm not trying to 'rip you off'.
DNA |
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| Eva |
| quote: | Originally posted by Pafi
OK, probably it is based on it, but I don't see any problem with this! His conclusion and solution is quite different.
Let him to be happy with that! I think your soultion is better (due to its simplicity), but his one can work too. |
Of course I leave him to be happy with a slightly different solution (which has theoretical background only). Anyway, there are several problems that arise even when simple paralleling is actually tried with real components. For example, at high currents the IGBT may turn on by itself while the MOSFET turns-off and Vce is rising due to reverse transfer capacitance, thus wasting part of the benefit. Another even funnier problem with paralleling is current bouncing action between both devices during turn-on phase, as each one is pulling down the gate of the other through reverse transfer capacitances and lead inductances, which usually results in a nasty oscillator during a few hundred nanoseconds. And finally, there is the classic diode reverse recovery problem.
What I claim is that I'm solving these issues in slightly unique ways, which I can no longer risk revealing. Also, IEEE papers tend to be beautiful from a theoretical point of view, but my experience is that they hardly cover the actual problems that arise when your target is to create a working product for a very demanding client and not just a thesis for university... I'd rather expend the membership money in components and stuff for experimentation... |
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| Eva |
| quote: | Originally posted by Genomerics
This time I was forced to look harder and I did try paralleling the IGBT with a mosfet to achieve zero current turn off. Unfortunately it did not work, in simulation, for me so I guessed about stored charge and came up with the reverse bias/charge removal idea that is shown on the web page.
I did a patent search to see if there was something similar about and found things like....
But nothing that mentioned applying a reverse bias to the CE terminals to remove stored charge so I went and put a patent in. It's not a very good one and I doubt if anything will come of it which is why I published the web page.
Like I say I gave you the link because I know you are working on similar stuff and might be interested. I really did come up with the idea independantly. If you have something that works for you and it is simpler then that's great but please believe me.....
I'm not trying to 'rip you off'.
DNA |
Then please accept my apologies. However, I must still criticise the fact of trying to file a patent on something that you haven't even tried and measured with real components (while somebody else may have it working and will be in trouble the patent is accepted). Hunting patents in that way is a truly unfair thing. Finally, if you accept some advice, stop trusting simulation when switching behaviour of transistors is involved, software is intended for more conceptual work (like control-loop modelling) and it usually gets all low-level switching plots wrong. Software told you that direct paralleling wasn't going to work, while it can actually achieve complete current-tail killing with latencies below 200ns (depending on IGBT choice).
EDIT: Concerning these two Japanese patents that you cited, note that they leave the unexpected problems that I explained unsolved.
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| Genomerics |
No worries......
Regarding patents. I'm not really in a position to defend them both in the legal and moral sense. However if you have commercially sensitive stuff then you can file for a patent or keep it secret and profit from it by using it. The patent route is considered pretty worthless by some people....
Don Lancaster
At best it just gives me a reference date. If someone else has done similar stuff prior to that then obviously my patent becomes invalid. If they do it later, and arrive at the idea independently, then yes it does seem unfair. However in my case I'm not likely to be chasing them.
It's not actually necessary to physically 'prove' that the idea really does work. There may be some part of patent law that restricts you in that area as well. Again I suppose it seems unfair but if an idea does work then it works. If someone is going to implement it then, as you have said and know, there will other problems.
At the end of the day if I come up with something that is 'new' and worthwhile what should I do with it? It's not as if I haven't invested time and effort in getting there. Is it fair that I give it over to MegaBuck Incorporated without some form of recompense?
That's going to happen anyway.......
I accept some of what you say about modelling but a lot of that is down to experience, how you use the software and how much you believe the results. Certainly in this case I had been using some ST IGBT models and quite frankly they were Rubbish. The IR model I ended up working with was much more believable.
When I have a bench to work at I use Spice as a thinking tool. It's just too easy to waste time prodding about in the guts of something that is misbehaving when what you need to do is get away from it and think. It has also been extremely useful in gaining insight into what might be happening and also learning things I thought I knew. It's good for demonstrating stuff as well...
Snubbing
I haven't added to that but there is something about reverse recovery of the output diodes and leakage inductance in the transformer that results in the voltage spike during diode turn off. I wouldn't have figured it out without modelling it in Spice and seeing what the 'idealised' waveforms were doing. It is cute.
I am biting my tongue here. However I have seen too many people rubbish simulation only to find that they have implemented things that were 'silly' and simulation would have given them some idea of how silly they were being. On the other hand I have also seen people simulate things and get the wrong answer as well......
I use both, believe neither, and question the results from each side until I understand what is going on and what compromises are being or have to be made. Ultimately it's about experience and how you gain it but I do not think it is right to just adopt a hard nosed opinion about simulation and throw it and people who use it in the bin.
No, the Japanese patents don't cover 'problems'. No, mine doesn't cover them either. However I can guess at some of them and, if and when I do build one, will have to sort out the other ones that crop up as well. However you had to have the original problem to think up a solution to it and then discover solutions to the problems that cropped up.
Yes, I believe that using the 'right' IGBT will 'improve' the situation but I'd rather have something that 'solves' it for all cases. I'm not being so bold as to say what I've suggested does but I'll be trying it. You mention problems with direct paralleling but the method I'm proposing is not really direct paralleling so it may overcome some of those problems and throw up ones of its own.
And, yes, I will be trying the resonant diode soft recovery technique. And yes..... I will be modelling it before I implement it to gain some insight as to what is really going on.
Anyway, it's about time for lunch for us English type people and your lot is on the same time line, sort of, so have a tasty one.
DNA |
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| ChocoHolic |
...I am really wondering how to measure such high efficiencies...
If I look to the specs of normal equipment then I am finding accurracies like +/-1% for normal DC measurements. For AC at 50 Hz also, but already for AC power where we have to take into account phase shift and harmonics I am happy if I can measure the power with +/- 3% overal accuracy with professional equipment (forget my hobby instruments at home). And if things are coming to amp output with several kHz..., then power is really hard to measure high accuracy. Even if we assume perfectly resistive load and just measure the voltage, you usually can expect a power tolerance of again +/-2%...
So even if professional equipment is telling us 95% efficiency from AC power input towards amp output... we must consider that it is 95% +/-5%... means: Something between 90% and 100%.
Or do I miss something?
On the other hand it is better not look to the accuracy specs of measurement equipment and better not to do a measurement error analysis, because it's time consuming and usually frustrating...
So for my DIY projects I have simplified things:
If it is small and cool, then efficacy is OK. :D |
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| fokker |
| quote: | Originally posted by ChocoHolic
...I am really wondering how to measure such high efficiencies... :D |
why bother with measuring? I thought it has been a tradition for some on this forum to just deem anything from others to be of a low enough efficiency. does 30% ring a bell for you? |
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| ChocoHolic |
...well, if a class D amp shows only 30% efficacy... YES, then some alarms bells would ring ...
And in fact finding out if you are around 30% or around 90% is easy to measure.
But I am bothering, because this thread here is discussing if it is 91% or 94%. Unfortunately there is quite a good chance that exactly one and the same proto would show 89% when measured with equipment A , but when measured with equipment B it would show 96%.... |
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| powerbecker |
Jaka,
".....this is my last post here. This forum has deteriorated low enough"
Right because of that it will be really a pity to lose you, please think about!
Regards
Heinz! |
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| IVX |
| quote: | Originally posted by powerbecker
Jaka,
".....this is my last post here. This forum has deteriorated low enough"
Right because of that it will be really a pity to lose you, please think about!
Regards
Heinz! |
I agree, absolutely! :cool: |
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| Genomerics |
Yes, I am also troubled by you leaving this Forum.
I notice that you have gone elsewhere and you are already discussing the opportunity of parallel operation of power stages.
Please come back and explain how this should be done.
Then we can get Eva to build some for us.
DNA |
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| IVX |
| About precision of the efficiency measurement, it is really important if true RMS V/A meter in use (even for design with PFC), otherwise, with some type of multimeters, >100% we can get yet. :) Funny, efficiency of the my regenerator circuit (input =230VAC@THD=3% to output =AC230VAC@THD=.00_%), obtained by the cheap multimeter = 98%+@500W, but it's two convertors -PFC+H-bridge! So, if that multimeter have quasy peak nature of measuring, the error can be up to 3%(input AC)+~1..2% (PFC current THD). I'll try my PCI oscilloscope as true RMS meter, i guess, that 10bit precision enough. |
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| poobah |
Darn!
I missed another good brawl here. |
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| LineSource |
How about the challenge of high'ish efficiency for a very low 0.15 ohm resistive load ribbon speaker?
I went to the Infineon site and noted that their Optimos3 IC process has a 30V, 100A N-MOSFET with 1.6 mohms of resistance. BSC016NO3LS G It does have 10,000pF of input capacitance, but the larger die area offers 1 C/W thermal resistance, while smaller MOSFETs with 3mohm resistance and 7,000pF input C have 1.3 C/W.
Can this team figure out how to drive it for good sound?
So, what size of output inductor would this need for 20 watts with a 430Khz TI xx5261 digital amp chip? All digital up to the speaker would be the goal, even with the non-feedback TI signal path.
http://www.infineon.com/upload/Docu...03LS_rev1.0.pdf
http://www.infineon.com/cgi-bin/ifx...ageTypeId=17099 |
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| IVX |
LineSource, very interesting task! IMO, 1.6mOhm quite enough to drive 150mOhm speaker, but you are right, passives like L and C would be trouble, body_diodes recuperation, PS decoupling = horror.:dead:
BTW, IRF6618 30v 1.7mOhm 5640pF |
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| fredos |
Drive it with TC442* serie of 9A mosfet driver...And use a hight saturation MPP output coil in ZVS topology ( output switch open in syncronisation with recovery of the output coil..), you will be able to achieve low switching lose for your load....And recovery will not be a probleme!
Fredos |
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| Eva |
| Diode recovery is not a problem for very low voltage MOSFETs, check diode reverse recovery charge in datasheets. Also, if gate capacitance becomes too large, resonant gate drive may be employed to reduce driver current and dissipation requirements considerably with a fixed switching delay as the only disadvantage. Brute force resistive high current gate drive is not always the best alternative. |
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| IVX |
| BTW, what kind/model of the ribbon speaker, has 150mOhm, and how it's usually driven, stepdown transformer? |
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| LineSource |
| quote: | Originally posted by IVX
BTW, what kind/model of the ribbon speaker, has 150mOhm, and how it's usually driven, stepdown transformer? |
Hi IVX,
I have Apogee Full Range with a 84" x 2" ceramic magnet midrange ribbon and DIY with a 94" x 3" NdFeB magnet midrange ribbon, both with about 0.15 ohm resistive load. I have 1 ohm and 4 ohm step up transformers which show significant phase shift on a vector impedance bridge. I also used a non-inductive 1 ohm series resistor to get a load which my Krells can easily drive to far superior sound than with the transformers. I have designed a DIY 32 watt Class-A amp that can direct drive 0.15 ohms, but it burns 200 watts under full bias with 16 big Sanken output transistors. I also need a 14 opamp analog crossover to set up LR8 slopes, and their phase shifts and lack of room equalization bothers me.
SO
My next educational goal is for a full digital design from the CD/DVD player to the speakers. I was hoping a Class-D expert would spend some engineering to point me in the right technical directions, especially the output stage passive filters. Looks like some specialized inductors are required. The all digital path like the 432kHz TI xx5261 digital amp has some appeal to me, as it maintains a full digital path up to the speakers. This would allow me to build up a digital Xover and room equalization. I understand that there is no feedback loop with a TI xx5261, and that a robust power supply is required. If I can't find an all digital solution, I feel that I might as well just stay with my Class-A amps and analog crossovers. A hi/lo Class-A bias switch gives me some global warming savings.
The 1.6 m-ohm Infineon MOSFET I tagged looked like a pretty good starting point. |
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