What is the nominal voltage and current of the power adapter?
The nominal voltage of the power adapter usually refers to the open circuit output voltage, that is, no load, no current output voltage. It is also possible to assume that this is the upper limit of the output voltage of the power supply. For the internal use of the active voltage regulator unit or voltage reference components, in general, the use of high internal resistance DC voltmeter, you can directly measure the nominal voltage.
Generally speaking, even if the voltage of the city has a certain fluctuation, the output of the voltage is also steadily constant value. But for a small transformer market cheap, basically is the traditional core transformer with four rectifier diode bridge rectifier with a large filter capacitor, so if using ordinary numerical DC voltmeter to measure will be greater than the nominal voltage, the reason is the bridge rectifier output DC ripple.
Simple is a sinusoidal voltage signal is connected to the half cycle time chain, after a large capacitor will be flat, but still large ripple coefficient (ripple coefficient is the voltage fluctuation signal with the average value of voltage ratio, the more novel of Ming Dynasty is closer to the DC voltage).
Nominal voltage refers to the integration of this voltage over time, divided by integral time. A simple understanding is the average of time. If measured by an ordinary DC voltmeter, the measured value is very close to the maximum value of the voltage signal, so it is not accurate. At the same time, if the city power fluctuates, the output of this type of power 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 end, 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.
Nominal current of 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 power supply resistance. Cause two things, one is to generate heat, equal to the square of the output current multiplied by internal resistance, so the power will be hot. The other is that the output voltage changes to a nominal voltage minus the internal voltage drop, resulting in a lower output voltage.
The usual design usually 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 proportion. Each manufacturer can set a higher or lower proportion according to the different requirements of the load product. This current value is the nominal current.
For example, the nominal current of the IBM 16V 72W power adapter is 4.5A (16V * 4.5A=72W). 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.