In recent years, the contact network has encountered several discussions about the power supply voltage, the power supply, the power supply and the load matching. It was a common sense problem, but later found many friends to discuss, just say a few words here.

I think the typical problems are as follows:

1. What is the nominal voltage and current of the power adapter (hereinafter referred to as power supply)?

2, are the same nominal voltage power supply, the output current is different, can not be used in the same book?

3, exactly the same machine, other people's power temperature, my always hot, why?

4, the power supply nominal voltage is much higher than my book battery voltage, will not have an accident?

5, why is the original power supply theory usually than the original?

Wait。

Below I talk about the personal understanding, also please correct.

First of all, the nominal voltage of the power adapter usually refers to the open circuit output voltage, that is, no load, no current output voltage. It can also be considered as the upper limit of the output voltage of the power supply. For the internal use of the active power supply voltage unit or voltage reference elements, in general use the high resistance of the DC voltage meter can be directly measured nominal voltage (electromotive force should be used more accurate bridge method, belonging to the college physics experiment course, not much), even if the voltage fluctuation of the output of certain. Is firmly constant; but for small transformer market cheap, such as those used to like the Walkman, basically is the traditional core transformer with four rectifier diode bridge rectifier and a filter capacitor of the

Finished numerical so if using ordinary DC voltmeter to measure will be greater than the nominal voltage, because the output is the bridge rectifier for the fluctuating DC, is simply a sinusoidal voltage signal is connected to the half cycle time chain, after a large capacitor will be flat, but the ripple the coefficient remains high (ripple coefficient is the voltage signal fluctuation with the average value of voltage ratio, the smaller that is closer to the DC voltage), the nominal voltage refers to the voltage integral time integral of time divided by the simple understanding of time is, on average, if we use the normal DC voltage meter measurement, measurement the maximum value is very close to the voltage signal, so the uncertainty. At the same time, if the city power fluctuates, the output of this kind of power supply will change accordingly.

In general, ordinary power adapter real no-load voltage and nominal voltage is not entirely consistent, because the characteristics of electronic components may not be completely consistent, so to allow a certain degree of error, according to the need to use civilian control in 0.1% to about 5%. The smaller the error, the higher the consistency requirements of electronic components, the higher the cost of industrial production, the more expensive the price of course.

Second is the nominal current value of the power supply. Regardless of any power supply has a certain internal resistance, so when the power output current, will produce pressure drop in the internal, equal to the output current multiplied by the internal resistance of the power supply. Two things, one is to generate heat, equal to the square of the output current multiplied by the internal resistance, so the power will be hot, and the other is the output voltage into a nominal voltage minus the internal pressure drop, resulting in lower output voltage. Usually the design after considering the over heat problem, generally limiting a current value when the output current reaches the pixelcost output voltage is reduced to 95% of the nominal voltage, or other proportion, each manufacturer can set a higher or lower proportion of the load according to the different needs of products, the current value is the nominal current. For example, the nominal current of the ibm16V 72W power adapter is 4.5A (16*4.5=72, blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah). If the load resistance is too low, causing the output current exceeds the nominal current, there would be two things, one is the individual components due to the cooling capacity to burn more than fever caused by power failure, the other is a thermal design of a room, only the output voltage is further reduced, if too much may lead to load to reduce normal work.

To understand the above concepts, we can judge the second problems of this paper. The same nominal voltage power supply, the output current is different, can not be used in the same book. The basic principle is that the power supply with large nominal current can replace the power supply with small nominal current. Some friends have misunderstood, think that the power supply of large nominal current will burn the notebook, because the current is big. In fact, much current under the same pressure depends on the load, work is the book, when in high load operation, the current more books into standby when the current is small, the current is equal to the equivalent resistance in the voltage divided by the books of the books. The power supply with large nominal current has sufficient current margin, and will not overheat or output voltage is too low when the power supply is replaced by a small nominal current source. On the contrary, the small current power supply instead of the high current power supply has the above risk. But some people use 56W power instead of 72W it is also not what problem, reason is usually designed the power adapter to leave some margin, the power load must be less than the power, so that instead of in general use is feasible, but the power margin of the remaining few, once you pick books a lot of peripherals, such as the two USB hard disk, then CPU running at full speed, there is a base, a top speed CD-ROM Dupan, plus at the same time to charge the battery, estimated to be dangerous, to feel your power at any time