评《凶器是手机还是充电器？》-开关电源原理一体化开关电源,高频开关电源, 室外电源机柜,室内电源机柜, 华为开关电源

看了《凶器是手机还是充电器？》，以及各种清华大学教授的评论，才知道直到今天，大家对电源适配器的认识依然停留在上世纪古老的“线性电源”。更加诡异的是，我们国家这么多学习电源技术的学生和工作人员居然没有一个人站出来说说一个“现代的”开关电源的工作原理。我只是个普通的数码爱好者，不是电源专业的大学生或者教授，但开关电源还是知道那么一点点。而开关电源的工作原理或许跟这次电死人的事件有关。

“开关电源”并不是带开关按钮的电源，而是一种电压转换技术。这种电源技术通过实践证明安全性非常高。这种技术充斥在我们日常生活中每一个角落。手机、PSP、电脑、平板电视、日光灯、移动电源、各种车载电器……基本上只要带电的，都用到“开关电源”，这足以证明这种技术有多么的安全、成熟。

我之所以先说实践很安全，那是因为，在理论上，还是有那么一点点危险性的。

我们在中学学到的电源电压变换的知识，是从物理书上的电磁感应一节学到，大概意思是，两组线圈，通过电磁感应，来实现电压变换。这就是传统的“线性电源”。实践证明，这种老技术有很多缺点，电阻大，发热大，转换效率低，体积非常大，重量非常重，非常不方便携带，而且功率跟重量成正比。但是有一个好处：高压区和低压区物理上是没有连接上的。

而开关电源技术中，高压区和低压区是直接连接的。是的，你没看错，是直接连通。开关电源是利用交流电正弦波的特性来实现降压的。我们日常使用的交流电虽然是220V，但实际上电压每时每刻都有周期性的变化，最低0V，最高311V，而且还是以正弦波的特性。而且根据正弦波的图像我们可以得知，220V的电源周期中，总有那么几个微秒的时间交流电电压处于5V以下。如果你的眼睛反应够快，手按动开关的速度够快，你是可以直接把你的手机插在电源插排上，当交流电电压处于5V以下时，你就接通插排的开关。当交流电电压大于5V时，你就断开开关。通过精确的电压检测和快速高频率的开关动作，就可以直接把220V的电压降到5V，而不需要什么降压线圈。这就是开关电源的“开关降压”的原理。当然这样降压出来的低压5V电流是呈现脉冲的形式，再配上简单的稳压电路就能实现稳定的电流输出。（其实“开关降压”的方法有几种，原理都类似，这里我只用最易理解的那个方案进行说明。）

由于是采用电子开关进行降压，因此整个电源就可以做得很小，重量也很轻，电阻小，转换效率就非常高。但缺点也很明显：高压区和低压区是直接连通的，不是物理断开的，如果电子开关性能不稳定，在错误的电压上进行接通的动作，低压区的电压在那个瞬间就会偏高，可能高于人体可承受的36V，甚至可能达到最高瞬间电压311V。由于高压是瞬间的，持续时间很短，用电设备还不一定会击穿损坏，不过人体就很难说。或许有的人可以承受，有的人无法承受。但无论怎么说，原装正品的电源肯定会使用优质的原件和有完善的保护电路，而假货电源的零件质量难以保证。所以我们要使用原装电源。同时，从工作原理可以得知：“充电时不要打电话”这个说法是有科学依据。

谨以此文向清华叫兽致敬。由于我只是普通非专业人员，肯定有描述不恰当的地方，所以同时希望从事电源研发的真正专业人员来科普、辟谣。

Look, "the killer is a cell phone or a charger?" As well as the comments of various Tsinghua University professors, it is known that until today, people's understanding of power adapters remains in the old "linear power" of the last century. Even more weird, there are so many students and workers in our country who learn power technology and no one can stand out and talk about the principle of a "modern" switching power supply. I am just an ordinary digital enthusiast, not a power professional student or professor, but switching power supplies still know a little bit. The working principle of the switching power supply may be related to the incident of the electric death.

Switching power supply is not a switch button power supply, but a voltage conversion technology. This power technology has proved to be very safe through practice. This technology is flooding every corner of our daily life. Mobile phones, PSP, computers, flat-panel televisions, fluorescent lamps, mobile power supplies, all kinds of vehicle electrical appliances... Basically, as long as charged, switch power is used, which proves how safe and mature the technology is.

The reason why I first said that practice is safe is that, in theory, it is still a little dangerous.

The knowledge of the power voltage transformation we learned in the middle school is learned from the electromagnetic induction in the physical book. It is probably meant to mean that the two sets of coils can be transformed by electromagnetic induction. This is the traditional "linear power". It has been proved that the old technology has many shortcomings, such as large resistance, large heat, low conversion efficiency, very large volume, very heavy weight, very inconvenient to carry, and the power is directly proportional to the weight. But there is one advantage: the high pressure zone and the low pressure zone are physically not connected.

In the switching power supply technology, the high voltage area and the low voltage area are directly connected. Yes, you're not mistaken. It's directly connected. The switching power supply uses the characteristic of the alternating current sine wave to realize the buck. The alternating current of our daily use is 220V, but in fact the voltage varies periodically every moment, the lowest 0V, the highest 311V, and the characteristic of the sine wave. And according to the image of the sine wave, we can see that in the power cycle of 220V, there are always several microseconds of alternating current voltage below 5V. If your eyes are quick enough and the hand moves fast enough, you can plug your cell phone directly into the power supply. When the AC voltage is below 5V, you connect the switch. When the alternating current voltage is greater than 5V, you disconnect the switch. By accurate voltage detection and fast and high frequency switching action, the voltage of 220V can be directly reduced to 5V without any buck coils. This is the principle of switching power down of switching power supply. Of course, this low voltage 5V current is a form of pulse, and a simple voltage regulator circuit can achieve stable current output. In fact, there are several methods of "switching down", which are similar in principle.

Because the electronic switch is used for step-down, the entire power supply can be made very small, the weight is light, the resistance is small, and the conversion efficiency is very high. But the shortcomings are also obvious: the high pressure area and the low pressure area are directly connected, not physically disconnected, if the electronic switch performance is unstable, on the wrong voltage to carry on the action, the voltage in the low voltage area will be higher at that moment, may be higher than the human body can bear the 36V, or even the maximum instantaneous voltage 311V. Because the high pressure is instantaneous and the duration is very short, the electrical equipment will not necessarily break down, but the human body is hard to say. Maybe some people can afford it, some people can not afford it. But no matter how it is, the original genuine power will definitely use high quality original and perfect protection circuit, and the quality of the parts of the fake power supply is difficult to guarantee. So we have to use the original power supply. At the same time, from the working principle, we can learn that there is a scientific basis for saying "don't call while charging."

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I would like to pay tribute to the beats of Tsinghua. Because I am only an ordinary non professional person, there must be a description of the inappropriate place, so at the same time, I hope that the real professionals engaged in power research and development to come to popular science and refute the rumor.