The main parameters of the laptop power adapter
2022-12-08 Views：40
Today, let's learn to understand what are the main parameters of the laptop power adapter?
First of all, the nominal voltage of the power adapter usually refers to the open-circuit output voltage, that is, not connected to any load, no current output voltage value. Therefore, it can also be considered that this is the upper limit of the output voltage of the power supply.
For the power supply internal use of active voltage regulator unit or voltage reference components, generally speaking, the use of high internal resistance DC voltmeter can be directly measured nominal voltage (more accurate should use the method of potential bridge, belongs to the university general physics course experiments, not to repeat), even if the mains voltage fluctuations, the output is also a steady constant value; but for the market cheap small transformers.
For example, the kind used for Walkman and so on, basically a traditional core transformer plus four rectifier diodes bridge rectifier plus a large filter capacitor on the finish, so that if the use of ordinary DC voltmeter measured value will be greater than the nominal voltage, the reason is that the output of the bridge rectifier for pulsating DC.
Simply put, it is a sinusoidal voltage signal of the positive half-cycle connected into a time chain, after a large capacitor filter will become flat some, but the ripple coefficient is still very large (ripple coefficient is the amplitude of the voltage signal fluctuations with the voltage average ratio, the smaller the voltage closer to DC), the so-called nominal voltage refers to this voltage on the integration of time and then divided by the integration time, simple understanding is the time of The average value, if measured with an ordinary DC voltmeter, the measured value is very close to the maximum value of the voltage signal, so it can not be measured. At the same time, if the utility fluctuates, the output of this type of power supply will also change.
Generally speaking, the real no-load voltage of ordinary power adapter is not necessarily the same as the nominal voltage, because the characteristics of electronic components can not be identical, so allow a certain amount of error, the civil situation according to the needs of the use of control in the range of 0.1% to 5%. The smaller the error, the higher the requirement for consistency of electronic components, the higher the cost of industrial production, the more expensive, of course.
Next is the nominal current value of the power supply. Regardless of any power supply has a certain internal resistance, so when the power supply output current, it will produce an internal voltage drop equal to the output current multiplied by the internal resistance of the power supply.
This leads to two things, one is the generation of heat, equal to the square of the output current times the internal resistance, so the power supply will be hot, and the other is the output voltage becomes the nominal voltage minus the internal voltage drop, leading to a lower output voltage. The usual design after considering the heat dissipation problem, generally limit a current value, when the output current reaches this worth, the output voltage is reduced to 95% of the nominal voltage, or other ratios, each manufacturer according to the different needs of the load product can set a higher or lower ratio, the current value is the nominal current.
For example, the nominal current of the 72W ibm16V power adapter is 4.5A (16*4.5=72). If the load resistance is too low, resulting in the output current exceeds the nominal current, generally two things will happen, one is the individual components due to heat over the cooling capacity resulting in burn caused by power damage, the other is the cooling design to leave a margin, only reflected in the output voltage is further reduced, if reduced too much may lead to the load can not work properly.
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