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Definition of Nominal Voltage and Current in Power Adapters

source:Industry News Popular:adapter release time:2022-04-16 09:26:55 Article author:yu

  Definition of Nominal Voltage and Current in Power Adapters(图1)

  The nominal voltage of the power adapter usually refers to the open-circuit output voltage, that is, the voltage value that is not connected to any load and has no current output. Therefore, it can also be considered as the upper limit of the output voltage of the power supply. For the case where an active voltage stabilization unit or a voltage reference element is used inside the power supply, generally speaking, a DC voltmeter with high internal resistance can directly measure the nominal voltage. Even if the mains voltage fluctuates to a certain extent, the output is stable. constant value.

  But for the cheap small transformers on the market, it is basically a traditional magnetic core transformer plus four rectifier diode bridge rectifiers plus a large filter capacitor. In this case, the value measured by an ordinary DC voltmeter will be larger than the nominal value. Voltage, the reason is that the output of the bridge rectifier is pulsating DC, which is simply a time chain connected by the positive half-cycle of the sinusoidal voltage signal. After filtering with a large capacitor, it will become flatter, but the ripple coefficient is still large ( The ripple coefficient is the ratio of the amplitude of the voltage signal fluctuation to the average value of the voltage. The smaller the voltage, the closer the voltage is to DC). The so-called nominal voltage refers to the time integral of this voltage divided by the integral time. A simple understanding is the time 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 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 real 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 a certain error is allowed. %about. The smaller the error, the higher the consistency requirements of electronic components, the higher the cost in industrial production, and of course the more expensive the price.

  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, a voltage drop will be 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 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, causing the output voltage to drop.


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