What are the nominal voltage and current of the power adapter?

Since the advent of smart portable devices, people have been dependent on Power Adapters.In daily life, sometimes it is necessary to use a non-supporting Power Adapter to charge the situation, in this case, people need to have a sufficient understanding of the voltage and current marked by the external power adapter, this article will be based on the two values for you to explain.

First of all, the nominal voltage of the power adapter usually refers to the open output voltage, that is, no load, no current output voltage value.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 unit or voltage reference element inside the power supply, generally speaking, the use of high internal resistance of DC voltmeter can be directly measured nominal voltage (more accurate should use the method of electromotive force bridge, which belongs to the university general physics class test, not to describe), even if the mains voltage occurs certain fluctuations, its output is stable constant value.

However, for the cheap small transformers on the market, it is basically the traditional magnetic transformer with four rectifier diode bridge rectifier and a large filter capacitor. In this way, if the ordinary DC voltmeter is used, the measured data will be greater than the nominal voltage, because the output of the bridge rectifier pulsates DC.In simple terms, it is a time chain formed by the positive half circumference of a sinusoidal voltage signal, which becomes gentler after large capacitance filtering, but the wavelet coefficient is still large (ripple coefficient is the ratio between the amplitude of voltage signal fluctuation and the average voltage, the smaller it is, the closer it is to DC). The so-called nominal voltage refers to the integration of this voltage over time and then divided by the integration time.Simple understanding is the average value of time, if the ordinary DC voltmeter measurement, the measured value is very close to the maximum value of the voltage signal, so the measurement is inaccurate.At the same time, if the mains fluctuate, the output of this type of power supply will also change.

Generally speaking, the real no-load voltage of the ordinary power supply is not necessarily consistent with the nominal voltage, because the characteristics of electronic components can not be completely consistent, so there is a certain amount of error allowed, civil use needs to be controlled at about 0.1% to 5%, the smaller the error on the consistency of electronic components, the higher the cost of industrial production,The more expensive it is.

Next is the nominal current value of the power supply.Any power supply has some internal resistance, so when the power supply output current, there will be an internal voltage drop (output current times the internal resistance of the power supply).This leads to two things: heat (equal to the square of the output current times the internal resistance) is generated, so the power supply heats up;The other is that the output voltage is the nominal voltage minus the internal voltage drop, resulting in a reduction in the output voltage.

The usual design after considering the heat dissipation problem, generally limited a current value, when the output current reaches this value, the output voltage is reduced to 95% of the nominal voltage, or other proportions, the manufacturers according to the different needs of the load products can be set higher or lower proportion, the current value is the nominal current.For example, the nominal current of A 72W ibm16V power supply 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 exceeds the heat dissipation capacity leading to power burn out;The other is that the heat dissipation design has a margin, which is only reflected in the further reduction of the output voltage. If the reduction is too much, the load may not work normally.

It can be seen from the above introduction that the nominal voltage of the ordinary power adapter is likely to be not equal to the real no-load voltage. This is mainly because the characteristics of the electronic components make the two values impossible to be exactly equal, and there must be some error between the two.This error should be taken into account by the users. I hope you will learn something from this reading.