- Electrical efficiency
The efficiency of an entity (a device, component, or
system) in electronicsand electrical engineeringis defined as useful power output divided by the total electrical power consumed (a fractional expression), typically denoted by the Greek letter small Eta (η).
Efficiency of typical electrical devices
"Efficiency" should not be confused with "
effectiveness": a system that wastes most of its input power but produces exactly what it is meant to is effective but not efficient. The term "efficiency" only makes sense in reference to the wanted effect. So a light bulbmight have 2% efficiency at emitting light yet still be 98% efficient at heating a room. (In practice it is nearly 100% efficient at heating a room because the light energy will also be converted to heat eventually, apart from the small fraction that leaves through the windows). An electronic amplifierthat delivers 10 watts of power to its load (for example a loudspeaker), while drawing 20 watts of power from a power source is 50% efficient. (10/20 × 100% = 50%)
* Electric kettle: over 90% (comparatively little heat energy is lost during the 2 to 3 minutes a kettle takes to boil water).
four-quadrant gateis highly effective, yet it has an electrical efficiency close to 0%.
Efficiency of devices at point of Maximum Power Transfer
As a result of the Maximum Power Theorem, devices transfer maximum power to a load when running at 50% electrical efficiency. This occurs when the load resistance (of the device in question) is equal to the internal
Thevenin equivalentresistance of the power source.
Efficiency of light bulbs
Incandescent light bulb: about 2%.
Compact fluorescent lamp: about 7% to 9%.
Light-emitting diode(LED) about 4% to 10%.
High efficiency is obviously desirable when we wish to
design systems that can operate from batteries. Inefficiency has a cost (either paid to the power company or the cost of the required power supply) to be weighed against the cost of attaining greater efficiency (choosing different components or redesigning the system). Also, any difference in the input and output power probably produces heat within the system (though noiseand other mechanical vibrations involve at least theoretically separate inefficiencies), and that heat must be removed from the system if it is to remain within its operating temperaturerange.If the system is in a climate controlled environment (e.g. a home or office), heat generated may affect heating, ventilation and air conditioning costs.
List of electronics topics
* Maximum Power Theorem
* Other measures of efficiency:
Performance per watt
* Efficiency improvement initiatives:
One watt initiative
* [http://www.sengpielaudio.com/calculator-efficiency.htm Conversion: Energy efficiency in percent of passive loudspeakers to sensitivity in dB per watt and meter]
* [http://www.iea-4e.org 4E - International Energy Agency Implementing Agreement to promote energy efficiency and standards for electrical products worldwide]
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