How do I Choose the Correct Laptop Adapter?

The power adapter is the source of power for the notebook computer. It contains a high-quality switching power supply. Its working principle is the same as the switching power supply in home appliances such as color TVs. Its role is to provide a stable low-voltage DC power for the notebook computer (usually at 12 ~ 19v).

Laptop power adapter

1: Varistor, its function is that when the external voltage is too high, the resistance of the varistor quickly becomes very small, and the fuse in series with the varistor is blown, thereby protecting other circuits from being burned. 2: Fuse, the specification is 2.5a / 250v. When the current in the circuit is too large, the fuse will blow to protect other components. 3: Inductive coil (also called choke coil), whose main function is to reduce electromagnetic interference. 4: Rectifier bridge, the specification is d3sb, the role is to change 220v AC power to DC power. 5: Filter capacitor, with a specification of 180uf / 400v, is used to filter the AC ripple in DC power, making the circuit more reliable. 6: op amp (integrated circuit), an important part of the protection circuit and voltage regulation. 7: Temperature probe, used to detect the internal temperature of the power adapter. When the temperature is higher than a set value (different brands of power adapters, the set temperature threshold is slightly different), the protection circuit will cut off the voltage of the adapter Output to protect the adapter from damage. 8: The high-power switching tube is one of the core components in the switching power supply. The switching power supply can work one on and one off. 9: Switching transformer, one of the core components in switching power supply. 10: Secondary rectifier, whose function is to change low-voltage AC power to low-voltage DC power. In ibm's power adapters, the rectifier is often operated by two high powers in parallel to obtain a large current output. 11: Secondary filter capacitor, with a specification of 820uf / 25v, two in total, which plays a role in filtering the ripple in low-voltage DC power. In addition to the above components, there are adjustable potentiometers and other resistance-capacitance components on the circuit board.

First, the nominal voltage of the power adapter usually refers to the open circuit output voltage, that is, the voltage value without any load connected and no current output. Therefore, it can be considered as the upper limit of the output voltage of the power supply. For the case where an active voltage stabilizing unit or a voltage reference element is used inside the power supply, in general, a DC voltage meter with a high internal resistance can directly measure the nominal voltage (more accurately, the method of the electromotive force bridge should be used, which belongs to university general physics Course experiment, not to go into details), even if the mains voltage fluctuates, its output is a stable and constant value; but for small transformers on the market, such as those used for Walkman, it is basically a traditional magnetic The core transformer plus four rectifier diode bridge rectifiers plus a large filter capacitor is done. In this case, if the value measured by an ordinary DC voltmeter is larger than the nominal voltage, the reason is that the output of the bridge rectifier is pulsating DC is simply a time chain connected by the positive half cycle of a sinusoidal voltage signal. After filtering by a large capacitor, it will become flat, but the ripple coefficient is still large (the ripple coefficient is the amplitude of the voltage signal fluctuation and the voltage The ratio of the average value, the smaller the voltage is closer to DC), the so-called nominal voltage refers to this voltage Points divided by the integration time, is simple to understand the average time, if measured with a normal DC voltage meter, the measured value is very close to the maximum of the voltage signal, the uncertainty. At the same time, if the mains power fluctuates, the output of this type of power supply will change accordingly. Generally speaking, the true no-load voltage of ordinary power adapters may not be exactly the same as the nominal voltage. Because the characteristics of electronic components cannot be completely the same, a certain error is allowed. The civilian situation is controlled to 0.1% to 5 according to the needs of the application. %about. The smaller the error, the higher the consistency requirements for electronic components, the higher the cost in industrial production, and the more expensive the price, of course. The second is the nominal current of the power supply. No matter any power supply has a certain internal resistance, when the power supply outputs current, a voltage drop is generated internally, which is 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 times 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, which causes the output voltage to decrease. The usual design generally limits a current value after considering the heat dissipation problem. When the output current reaches this value, the output voltage is reduced to 95% of the nominal voltage, or other proportions. Each manufacturer can set it according to the different needs of the load product. For higher or lower ratios, this current value is the nominal current. For example, the nominal current of a 72w ibm16v power adapter is 4.5a (16 * 4.5 = 72, nonsense). If the load resistance is too low, causing the output current to exceed the nominal current, two things usually happen. One is that the individual components are damaged due to heat generation and the power is damaged due to burnout. The output voltage is further reduced. If it is reduced too much, the load may not work properly.

Theoretically, the original power supply is relatively better, in fact, the difference may not be felt. The input voltage allowed by a normal load has a safe range, such as the nominal value plus or minus 5%. One example is that the input requirement of many 2.5-inch hard drives is 5v plus or minus 5%. The same is true for notebooks. If the input voltage is too large or too small, the protection circuit will operate and stop working. However, before the protection circuit operates, the internal voltage regulator circuit has been biased towards the upper or lower operating limit. In principle, it has a certain impact on the life of the device. However, from the perspective of today, the reliability of electronic components is quite good. Within the range, there are rarely problems, and the life will not be shorter than the life of books, so this is not the main problem. The more important problem may be the data security of the books. Sudden automatic protection to stop working is very scary for the computer, especially many friends who do not use batteries. Sometimes the computer's inexplicable restart is also related to this. For the original power supply, the manufacturer knows what kind of load to connect, so it can easily calculate the nominal voltage and nominal current of the power supply, that is, the nominal voltage of the power supply should meet the following two conditions. The first is At the maximum current output, the nominal voltage minus the voltage drop of the power supply itself should be greater than 95% of the voltage required by the load. Second, at the minimum current output, the design voltage minus the power supply voltage drop should be less than 105% of the voltage required by the load. However, if non-original adapters are used, such as general-purpose transformers, the above issues cannot be seriously considered. This is because users can only try to obtain compatibility from the power supply parameters, but the internal resistance of each adapter is different. The allowable error of the nominal voltage may be different, and the definition of the range of voltage change at the nominal current output may be different. It is not necessarily even if the output ripple coefficient is small enough. If the output power and output voltage are not carefully measured, In principle, there is a certain risk, but this risk is small, because as long as you choose a power supply with a large enough nominal current, the problem of excessive internal resistance will not occur, and the ripple coefficient can also be obtained by internal voltage regulation. Reduced, so I said that the original power supply is usually better than the non-original power supply. This is the difference between the original power supply and the ordinary power supply.

Because the power adapter is a switching power supply that works under high voltage and high current conditions, the workload is relatively heavy, and it is a fully enclosed structure. There are no heat dissipation holes in the housing, and there is no fan inside to assist heat dissipation. The internal temperature is high. Especially in the hot summer, if you touch the surface with your hand, you can feel hot, and the internal temperature is higher. Therefore, in daily office and entertainment, it should be properly maintained and maintained. 1. Create a good cooling environment. When using the notebook in a high-temperature environment, the power adapter should be placed in a place that is not exposed to direct sunlight and ventilation; do not place the power adapter near the notebook's cooling air outlet, otherwise not only the heat of the power adapter cannot be emitted, but also To absorb part of the heat. In the hot summer, we can put the adapter on its side to increase the contact area between the adapter and the air, so that the heat of the adapter can be better dissipated. In order to obtain better heat dissipation, we can also insert a narrow plastic or metal block between the adapter and the desktop to increase the air convection speed around the adapter and accelerate the heat dissipation of the adapter. 2. Stop using it in case of abnormality. When the power adapter emits a large working noise or even smoke, it is often damaged or malfunctioning, so it should be stopped immediately, and it can be put into use again after being inspected by a professional engineer. 3. Use caution when using non-genuine power supplies. Non-original power adapters may have some differences in the output interface, voltage, and current values (or they are not the same as the actual ones). Improper matching may affect the stability of the notebook, or even more serious consequences. In addition, the power adapters of notebooks of the same brand and different models should also be used with caution. We will introduce this aspect in detail later.