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How to Calculate the Efficiency of Electronics

In most cases, efficiency is a desirable quality because inefficiency entails wasted energy. Calculating the efficiency of electronic circuits can be complex and details-heavy, although efficiency itself is a relatively simple and straightforward concept. Efficiency is an electronic device's output energy compared to all of its inputs; although high efficiency can be important, engineers also take other qualities into consideration when choosing circuit and component designs.

General
- In its most basic form, efficiency is the percentage you get when you divide a circuit's output power, voltage or other quantity by its inputs and multiply by 100. No electronic system is 100 percent efficient, nor can one exceed 100 percent; some energy is inevitably wasted as heat and other undesirable forms of energy. To take an example, a certain electronic circuit uses 10 watts of power from a standard household outlet and delivers a five-watt signal at its output. The circuit's efficiency is (5/10) * 100, or 50 percent.
Amplifiers
- Because dozens of different amplifier designs exist, engineers have broken them down into a handful of classifications designated by letters such as "A," "B" and "C." As you progress down the alphabet, the amplifier's output quality becomes less while the efficiency increases. For example, a "Class A" amplifier has the best signal quality but the worst efficiency -- typically between 20 and 50 percent. At the other extreme, a traditional "Class D" amplifier has poor signal quality but efficiencies better than 80 percent. Calculating an amplifier's efficiency is as simple as dividing the output power by the supply power and multiplying by 100.
Speakers
- A speaker's efficiency is its acoustic output power divided by its electrical input power times 100. Acoustic power comes in units of watts, as does electric power. Because speakers have poor efficiency -- a few percent in most cases -- they waste significant amounts of energy as heat. Speakers that run on more than a few watts of power therefore run hot and require sturdy construction to manage the heat.
Power Supplies
- A power supply is an electronic device that takes in standard 120-volt household current and converts it to low-voltage direct current. Electronic equipment designers value high-efficiency power supplies because they run relatively cool and save energy. To calculate efficiency for a power supply, multiply the output volts by the amps of DC current, divide the result by the product of AC input voltage and current and then multiply the total by 100.

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