In fact, strictly speaking, this "plug" is called a switching power adapter, and the purpose is to convert the AC power from the power grid into DC power into the electronic device. The laptop's power adapter is bigger, and it is more convenient to warm your hands in winter~
So why replace the alternating current with direct current? Let us start from the beginning.
Electricity is a natural phenomenon. Static or moving charges can produce a lot of interesting physical phenomena, such as lightning that can be seen in thunderstorms, and sparks when you take off your sweater in winter. Later, scientists discovered the law from various electrical effects, and invented batteries, generators, and electric motors.
Do you use DC or do you use AC?
220 volts / 50 Hz AC is China's power supply standard, so many people think that household appliances are all AC. As for the DC power, probably except for the "DC inverter air conditioner" that will be chanted in the advertisement, I can't think of anything else.
In fact, DC applications are widely used, and you have definitely seen them and used them. such as:
definition
Direct current is the current whose direction does not change with time.
AC power is the current that changes periodically in both size and direction.
Observed from the oscilloscope, one is straight, one is curved...
Anyway, it's all electricity, and the difference is not big?
No~ No~ No~
Let's turn history and talk about gossip!
DC power is the pioneer of the power revolution. In the early days of electromagnetic experiments, people always tried to convert the generated electric energy into direct current.
In 1879, Thomas Edison made the first carbon-silver incandescent lamp, which attracted a lot of investment. Since then, Xiao Ai’s classmates have been on the road. On a night in 1882, 110 volts of DC power was delivered to the entire block of Manhattan, New York... You can finally throw away the kerosene lamp~
However, the drawbacks of DC transmission are gradually manifested as the range of use is expanded: in the case of constant voltage, the increase in power supply distance and the increase in users exacerbate line losses. The power supply area of ​​the small DC central power station is limited to a radius of less than 2 kilometers.
Since the amount of loss = current 2 ✕ resistance, reducing the current can reduce the loss.
When the transmission power remains the same, the current is inversely proportional to the voltage, so increasing the voltage reduces the current and reduces the loss.
At that time, the high-voltage DC technology was still not mature, and the DC voltage transformation was more complicated. At this time, Serbian young Nikola Tesla carried a school bag and ran across the ocean to the idol Edison. He has a less mature little suggestion - AC transmission. The AC motor is simpler than the DC motor structure and is easy to be transformed. It can solve the problem of increasing the transmission voltage simply, economically and reliably.
However, this proposal was rejected by the overbearing president. Some people say that because the little love classmates did not learn a few days, do not understand the high number, the exchange of electricity is a bit abstract for him. In order to obstruct the development of AC, Edison not only did the radio and death experiments in the public, but also launched the media to report the AC accident, and also promoted the invention of the electric chair - the execution of the death penalty.
Of course, in this dispute between AC and DC, the AC with the advantage of long-distance transmission still won. (Note, here is the transmission.)
AC, DC, who is better?
As the line voltage continues to increase, the transmission power and the transmission distance continue to increase, and the DC power is favored by engineers. Because DC power does not require rectification and filtering, there is no phase difference and it is relatively stable. How to boost the DC power? Simply put, the boosting work is handed over to the AC, and the AC and DC converters are just fine. Moreover, from the economic point of view, although the DC converter station has a higher cost than the AC power transmission substation, the DC line As long as the two lines are positive and negative, the three-phase line of the AC line requires three lines, and the cost of the DC line is lower. Therefore, the longer the distance, the more suitable for DC transmission.
For example, the current highest voltage transmission project in the world is the DC project - ±1100 kV Zhundong-Hainan Engineering. The total length of the project line is 3,324 kilometers, which is longer than the straight line distance from Harbin to Haikou.
In the field of transmission, the underwater cable of more than 30 kilometers and the asynchronous connection between the two AC systems are also used for direct current.
Both AC and DC have their own characteristics. Some people say, for example, an AC like a high-speed railway, a DC like an air plane, a midway stop, and a point-to-point flight. Which one to use, specific analysis of specific issues.
Do you want to use DC power for household appliances?
Back in the field of household appliances, DC products are used inside IT products (such as mobile phones, computers) and most home appliances. Because notebooks and mobile phones are demanding, the rectifiers are placed outside, while desktop computers, refrigerators, and air conditioners put the rectifier inside the appliance.
Why? Back to the essence, DC power continuously flows from the positive pole to the negative pole, and the alternating current is fluctuating. The electronic components work by recognizing high and low potentials. For example, a computer has a potential of 1, and no potential is 0. The alternating current itself has a potential of zero crossing, so that electronic components cannot perform correct logic judgment.
Electricity is an evolving and complex science, and this article clearly cannot explain every situation in detail. However, if the girlfriend asks "Is there a charging plug with a mobile phone?" You can take this article with ease and correct it: "Dear, this is called a power adapter." - A suggestion from a single dog.
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