Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [efficiency]

A measure of the overall effectiveness of a system. For example, in power conversion, it would be the ratio of output power to input power.

Efficiency is the fraction of a quantity that can be used to perform a desired task. For example, in power conversion and transmisison systems it would be the fraction of the input power that reaches the output load. Typically, the more efficient a system is, the better.

The term can also be applied in other ways. In information processing and communications, efficiency can refer to the fraction of physical bits or symbols that actually convey application data, as opposed to "overhead" bits used for synchronization or error detection/correction.

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Why are car batteries still so heavy?

Back when I was a kid, car batteries used to be huge heavy lumps of plastic filled with lead and acid. They used to weigh almost as much as a mobile phone (slight exaggeration there, sorry). 45 years later, car batteries still look the same and…
user130311
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How efficient are LEDs?

Generally I see efficiency related to the lumens per watt, but what is the actual typical efficiency of LEDs in terms of electrical energy in to optical energy out? What sort of conversions apply?
Dirk Bruere
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Why does this LED bulb have an energy efficiency rating of 'F'?

In my home, I have some halogen spot lights, which have an energy efficiency rating of 'C': I would like to replace them with more efficient LED bulbs, but looking on the Philips website, they claim their bulbs are rated 'F'! LEDspot VLE GU5.3 MR16…
Rocketmagnet
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Computer power supplies usually have higher efficiency on 230V than on 115V. Why?

As seen here in the example, this particular power supply (and most others too) has higher efficiency when running on 230V. Given that computer power supplies are usually required to output a combination of 12V, 5V, and 3.3V DC, why is it that…
cyqsimon
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Why don't we use GaN transistors everywhere?

There has been a lot of research around GaN transistors, proving that they have a very low on-resistance, low gate-charge and are very effective at high temperatures. So why are we still mostly producing Si transistors? Even if the GaN transistor is…
Casper Vranken
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If we could start our electrical grid from scratch with today's technology, which would be the most efficient choice? AC or DC?

Lately, I’ve been reading about the many advantages of HVDC transmission systems for long distance transmission, undersea links, and others. The historical reason of why AC was picked over DC was mostly due to the invention of the transformer, which…
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How are LEDs considered efficient?

I've always found circuits containing LEDs hard to understand, please bear with me. I know most people find it easy, but I'm confused by them so some of my assumptions might not be correct, please correct me if that's the case. So onto the question:…
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How could have Banksy kept an RF receiver running for 12 years?

I'm talking about Banksy's "Girl with balloon" painting that shredded itself at auction. I think the general consensus is that he didn't, and that it was set up before the auction (or a couple years ago, not 12 years). But lets say he did, how could…
Daffy
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Gate capacitance vs. Gate charge in n-ch FETs, and how to calculate power dissipation during charging/discharging of the gate

I am using a MOSFET driver (TC4427A), which can charge a 1nF gate capacitance in about 30ns. The dual N-ch MOSFET I am using (Si4946EY) has a gate charge of 30nC (max) per fet. I am only considering one for now as both on the die are identical. I…
Thomas O
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What drives the advancement towards ever faster cellular network speeds?

I've always accepted that technology advances. Being born in the 90s, everything just becomes faster, smaller, cheaper and generally better if you wait a few years. This was most obvious with consumer electronics such as TVs, PCs and…
freejuices
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Efficient low power regulation? i.e. 9 -> 5 Volts

For the sake providing as much current as possible to a small circuit, regulated down from ~9V to 5V (or 5V->1.5V), I have looked at some possible options. What I was originally going to do (maybe a regulator for a solar cell, or 9v battery) is the…
Hobbyist
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Step voltage up or step voltage down when using batteries?

When using batteries to drive a load via a voltage regulator, is it better to step the voltage up from two batteries in parallel, or step the voltage down from two batteries in series? If there is no absolute answer, is there a general rule (or set…
Polynomial
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Can a charge-pump be 100% efficient, given ideal components?

A recent question about cyclically charging a capacitor reminded me of something I read once. As I remember, it demonstrated that it's impossible to construct a charge pump that is 100% efficient with ideal components, but it is possible to build a…
Phil Frost
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Voltage regulator from first principles - why is power dumped in the transistor?

I'm trying to further my understanding of electronics, so I decided to try to design a fixed voltage regulator capable of supplying an amp or so. I put this together from first principles without referring to any kind of reference on how voltage…
Polynomial
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What is the theoretical limit of lumen/watt for lighting systems?

Nowadays we see LEDs with 300 lumen per watt luminous efficacy. They still waste a lot of power as heat. Now what is the limit of electricity to light conversion? Say we build an LED with 100% efficiency, which doesn't waste any power as heat or…
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