tag 标签: efficiency

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  • 热度 23
    2015-9-18 18:15
    1613 次阅读|
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    Power supply efficiency is a "hot" topic these days, whether it's an AC/DC or DC/DC unit (sorry about that unavoidable pun). Everyone is concerned about it for reasons related to issues of one or more factors of run time, thermal load, operating cost, or regulatory mandates.   Of course, talking about it is one thing, but measuring it and doing it properly is another. In the "old days" when efficiencies were in the range of 40 to 80%, a measurement error of a few percentage points might not be a serious problem. As efficiencies are, however, now in the 85% to 90%+ zone and every percentage point increase is judged as critical, any inadvertent or unintentional errors in the test set-up or execution can be a major concern.   A recent blog post by Josh Mandelcorn at Texas Instruments' Power House site clearly showed how easy it is to allow apparently inconsequential or overlooked issues to seriously affect the validity of the results. He points out that the potential errors in the final results start with a basic fact: there are four simultaneous readings (input and output current and voltage) from four meters, and they each have errors which can conveniently cancel out, or just as easily add up.     In addition, the effect of temperature on wire and connector resistivity—not an issue with very low-power supplies, of course—can easily cause other small errors as well. Furthermore, there are issues associated with forced cooling versus convection cooling, thermal time constants for the supply's circuitry, and other factors that can affect the legitimacy of the numbers, even if they are measured with high accuracy.   It's an old story: making a fairly good measurement is often easy; making a really good one is much harder. As most engineers know, the difference between the two can become a serious problem. Even if the results are tagged as "preliminary, subject to review," they get repeated in reports and often develop a life and credibility of their own, at least in management's mind.   Pretty soon, the numbers become accepted as solid fact rather than as tentative subject to verification; for supplies, the rough number will soon become the lower-bound threshold of presumed efficiency. It’s tough to go back to the boss and say "you know that 94% number I gave you last week? —after careful review, it's really only 90%."   Have you have to make power supply efficiency measurements? What problems did you encounter, or not foresee? Did they come back and "bite you" when you had to re-visit them?
  • 热度 21
    2015-1-29 20:41
    1361 次阅读|
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    I am a staunch believer in the laws of thermodynamics and their plain-spoken corollary, "When it comes to energy, there is no free lunch." That's why I automatically dismiss any article or ad promising efficiency of 100% or better (you've likely seen the ones for products which promise to run your car on water or similar, or heard about "miracle machines" which produce more energy than they consume). Efficiency close to 100%, maybe -- but equal to or greater than 100%, sorry, I'm not even remotely buying it. That's why I was shocked when I saw the headline “ 8000% efficient LED enables ultralow-power data transmission ” in a recent article in Laser Focus World . Whoa…a little above 100% is one thing, but 8000% is truly an outrageous boast. I assumed it was a typographical error; they meant to write 80% and accidently added the zeroes in the headline.   It turns out, though, that the headline was correct. The improved efficiency has to do with how and where you measure input and output powers, plus the subtleties of LEDs and quantum mechanics. To quote the start of the article:   Certain LEDs, when heated and then run at a very low power, exhibit wall-plug efficiencies of more than 100%; this effect is explained by the existence of thermoelectric pumping of the LED… The setup transmitted 3 kbit/sec at a bit-error rate of 3 x 10 -3 and an energy expenditure per bit of only 40 fJ.   Roughly speaking, the LED is pumped with thermal energy in advance, then the energy is parceled out via optical data bits, while the LED itself does not need to consume additional corresponding power. (This effect goes by several names: electro-luminescent or EL cooling, electroluminescent refrigeration, thermophotonic cooling, and optothermionic refrigeration.) You can read the detailed, highly academic article on what these researchers did in Applied Physics Letters .   I'll admit, I only could follow a few of the details of their work, which included a highly specialized GaInAsSb/GaSb double hetero-junction LED. The report states, "The setup was able to detect light power of only 7.66 ±1.6 pW at an LED wall plug efficiency of 8000 ±1700%." I interpreted this to mean that the efficiency parameter had a tolerance of a little over 20%, which is either pretty good or pretty bad depending on your perspective. Power measurements, especially related to an ultralow-power optical regime rather than an electrical one, are very challenging to implement and fickle in their consistency. At these low powers, there isn’t a lot of headroom or range—every photon counts.   The questions I always have when I look at serious, legitimate research such as this are: how do you measure energy and power in this extreme low-power region with confidence? How do you know what you are measuring is what you actually intended to measure, rather than a measurement artifact unintentionally distorted by wishful thinking? How do you verify, and calibrate, the fundamental credibility of your instrumentation?   Have you been involved with ultra-sensitive electrical or optical power measurements? What steps did you have to take to instrument the setup and compensate for factors such as temperature shift?
  • 热度 21
    2014-6-18 18:06
    1808 次阅读|
    0 个评论
    We all know about the push for implementing diverse energy-saving technologies, and with good reason: They pay off in the long run. A few recent examples you may have read about include:   - Ford is switching the body panels of the F-150 pickup, its most popular truck, from steel to aluminum. This will reduce weight by several hundred pounds and increase gas mileage by a few mpg, but it will also raise the vehicle cost by a few thousand dollars. The switchover is not trivial; it requires huge changes in the supply chain, body panel design, production tooling, and manufacturing techniques. In addition, aluminum is much harder to repair in the field. Only a few body shops can handle it.   - Cars are being designed for "start-stop" operation, where the engine shuts off when the vehicle stops (no matter how briefly) and restarts when the gas pedal is depressed. Again, the objective is to save fuel. The cost is the need for a far more rugged design in the entire starter subsystem, as well as a very different internal construction of the vehicle battery. The need for frequent bursts of starting current (around 100 A) puts a very different battery charge/discharge curve and chemistry into play.   - To squeeze a little more operating efficiency and mileage out of the power train, the traditional three-, four-, and even five-speed transmission is being replaced in some vehicles with seven or more forward speeds. The penalties are the increased weight and size of the transmission, unknown long-term reliability, and, of course, higher initial cost.In a non-automotive application, we have the use of CFLs and LED-based lamps in place of the incandescent bulb, as dictated by building codes and other government mandates. Certainly, these newer technologies are much more efficient and last longer, but they are also more costly. An LED lamp costs between $5 and $10, while an incandescent bulb is less than $1 in many cases.   - In all these cases, the message is the same: Regardless of the up-front cost to the consumer, it's worth it because it will save energy and thus money in the long run. Economists call this ROI, for "return on investment."   But the dilemma is this: Not all consumers can afford to think in terms of that virtuous long run, nor can they measure the value of their expenditures in terms of cold, rational ROI. For many people, spending a few hundred extra dollars now -- to save that amount and more later -- is just not a viable option. They don't have the money, period. You could argue that it is somewhat presumptuous of those who have the funds available to insist that those who may not have them to do this for their own good, if only they could think of the long term and act accordingly.   That's why I am of two minds whenever I see yet another energy-saving product or program that says we need to invest (also known as "spend") money now in order to get recurring savings later. Certainly, the ROI may be favorable, but not everyone has the ability to make that up-front investment, regardless of how much sense it makes in the ideal world. In some ways, it's yet another manifestation of the many corollaries to the basic engineering design rule, "The perfect is the enemy of the good."   Have you seen an energy-saving design or strategy that assumed too much about the end user's situation? Which aspects do you consider unrealistic, and why?
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    时间: 2019-12-28 19:23
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    本应用笔记介绍了一个基于NXP半导体公司TDA8932B或TDA8933(B)D类音频立体声开关放大器(SMA)音频,已应用在平板电视的功放设备。AN10436TDA8932B/33(B)Class-DaudioamplifierRev.01―12December2007ApplicationnoteDocumentinformationInfoContentKeywordsClass-Damplifier,Highefficiency,Switchmodeamplifier,FlatTV.AbstractThisapplicationnotedescribesastereoSwitchedModeAmplifier(SMA)foraudio,basedoneithertheTDA8932BorTDA8933(B)Class-DaudioamplifierdeviceofNXPSemiconductors,whichhasbeendesignedforFlatTVapplications.TheTDA8932Bdeviceisthehigh-powerversionthatdeliversanoutputpowerof2×10WRMSto2×25WRMSinaSingleEnded(SE)……
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    时间: 2019-12-24 21:51
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    时间: 2019-12-24 20:18
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    上传者: rdg1993
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    时间: 2019-12-24 20:17
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    时间: 2020-1-13 14:35
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    AsimplemethodtocalculatepoweramplifierefficiencyversusoutputpowerproductforumAsimplemethodtocalculatepoweramplifierefficiencyversusoutputpowerLookingforanewmethodtosavevaluabledesigntime?ThisnewmethodallowsthedesignertoevaluateaPA’sefficiencywithoutactualbuildup.ByFrankDellaCortetransistors.Althoughnotnecessaryforthisdiscussion,aPAdesignerneedstoconsidertheoptimaloperatingpointforthePAtransistortoobtainmaximumefficiency.ForClass-ABmode,thePA’soutputpowercapabilityversusitsloadline(Rlcap)isgivenbythefollowingrelationship:Pcap=(Veff)2/2Rlcap,WhereVeff=Vcc-VsatOncetheloadlineisset,themaximumpowertransfer,hencemaximumPAefficiency,willoccurwhentheloadisequaltotheloadline.Thetypicalloadlinesfor3-voltPAsrunontheorderof2to5.Inpra……