Contact Private Network has encountered several discussions over the past year about whether the supply voltage, power supply, power supply, and load match. Originally, this was a common sense question, but later I found out that many friends had discussed it, so I will say a few words here.
I feel that the most typical problems are as follows:
1. What does the nominal voltage and current of the power adapter (hereinafter referred to as the power supply) mean?
2. They are all power supplies with the same nominal voltage and different output currents. Can they be used on the same notebook?
3. The same machine, other people's power supply is hot, mine is always hot, why?
4. The nominal voltage of the power supply is much higher than the voltage of my laptop battery, so there will be no accidents, right?
5. Why is an original power supply usually better than a non-original power supply in theory?
And many more.
Next, I will talk about my personal understanding, please correct me.
First, the nominal voltage of a power adapter usually refers to the open-circuit output voltage, which is the voltage value of the no-load, no-current output. Therefore, it can also be considered as the upper limit of the output voltage of the power supply. For the use of active voltage regulator units or voltage reference elements inside the power supply, in general, it is possible to directly measure the nominal voltage using a DC voltmeter with high internal resistance (more precisely, the method of EMF bridge) should be used, which belongs to university general physics. course experiments, will not be repeated), even if the mains voltage fluctuates to a certain extent, its output is a stable constant value; However, cheap small transformers on the market, such as the Walkman, are basically traditional core transformers plus four rectifier diodes, bridge rectifier and a large filter capacitor. In this case, if the value measured with a normal DC voltmeter is greater than the nominal voltage, it is because the output of the bridge rectifier is pulsating. Direct current, simply put, is a time chain connected by the positive half-period of sinusoidal voltage signals. The large capacitor will flatten after filtering, but the ripple coefficient is still very large (the ripple coefficient is the ratio of the voltage signal fluctuation amplitude to the voltage average, the smaller the voltage, the closer the voltage is to DC)。 The so-called nominal voltage refers to the integration of this voltage over time and then divided by the integration time. The simple understanding is the average of time. If measured with a normal DC voltmeter, the measurement value is very close to the maximum value of the voltage signal, so it is not accurate. At the same time, if the mains power fluctuates, the output of this type of power supply will also change accordingly.
Generally speaking, the true no-load voltage of ordinary power adapters is not necessarily exactly the same as the nominal voltage, because the characteristics of electronic components cannot be completely consistent, so certain errors are allowed. % about. The smaller the error, the higher the requirements for the consistency of electronic components, the higher the cost of industrial production, and of course, the more expensive it is.
The second is the nominal current value of the power supply. Any power supply has a certain internal resistance, so when the power supply outputs current, there will be an internal voltage drop equal to the output current multiplied by the internal resistance of the power supply. It causes two things, one is to generate heat, which is equal to the square of the output current multiplied by the internal resistance, so the power supply will heat up, and the other is that the output voltage becomes the nominal voltage minus the internal voltage drop, resulting in a drop in the output voltage. Typical designs typically limit current values after considering heat dissipation issues. When the output current reaches this value, the output voltage is reduced to the nominal voltage95%, or other percentages. Each manufacturer can set it according to the different needs of the load product. higher or lower ratio, this current value is the nominal current. For example, a 72W ibm16V power adapter has a nominal current of 4.5A (16*4.5=72, nonsense). If the load resistance is too low, causing the output current to exceed the nominal current, there are generally two situations. First, individual components are burned out due to heat exceeding heat dissipation capacity, causing damage to the power supply.
