I believe that power supply designers are not unfamiliar with power
adapters, but when we go deeper, do power supply engineers know enough about
power adapters? In fact, the discussion about power adapters in major forums is
almost the most basic. This article will explain the relationship between the
nominal voltage and current of the power adapter for novices.
It is not difficult to explain in terms of terms. The nominal voltage of
the power adapter usually refers to the open-circuit output voltage, that is,
the voltage value without any load and 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 regulator unit or a voltage reference element
is used inside the power supply, generally speaking, a DC voltmeter with high
internal resistance can be used to directly measure the nominal voltage (more
accurately, the method of electromotive force bridge should be used, which
belongs to the general physics of colleges and universities). Course experiment,
not to repeat), even if the mains voltage fluctuates to a certain extent, its
output is a stable and constant value.
But this only refers to the formal transformer, and for the cheap small
transformers on the market, such as those used for walkmans, it is basically a
traditional magnetic core transformer plus four rectifier diode bridge
rectifiers plus A large filter capacitor is enough. In this case, the value
measured by an ordinary DC voltmeter will be greater than the nominal voltage.
The reason is that the output of the bridge rectifier is a pulsating DC, which
is simply a positive half cycle of a sinusoidal voltage signal. The connected
time chain will become flat after being filtered by a large capacitor, but the
ripple coefficient is still large (the ripple coefficient is the ratio of the
amplitude of the voltage signal fluctuation to the average 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 average value of time. If it is measured with an
ordinary DC voltmeter, the measured value is very close to the maximum value of
the voltage signal, so it cannot be measured. allow. If the utility power
fluctuates, the output of this type of power supply will also change.
The real no-load voltage of an ordinary power adapter is not necessarily
exactly the same as the nominal voltage, because the characteristics of the
electronic components cannot be completely consistent, so a certain error is
allowed, and the civil situation is controlled at about 0.1% to 5% according to
the needs of the application. The smaller the error, the higher the requirements
for the consistency 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.
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 products.
Higher or lower ratio, this current value is the nominal current. For example,
the nominal current of a 72W ibm16V power adapter is 4.5A. If the load
resistance is too low, causing the output current to exceed the nominal current,
two things will generally happen. One is that the individual components burn out
due to the heat exceeding the heat dissipation capacity, causing the power
supply to be damaged. The other is that the heat dissipation design has a
margin, which is only reflected as The output voltage is further reduced, and if
it is reduced too much, the load may not function properly.
Read recommendations:
144W power amplifier power supply
S series S450 energy storage mobile power supply
151W bare board power supply
Reasons for Inrush Current in Switching Power Supply Design.adapter power manufacturer
Notebook computer power adapter manufacturers.power adapter wholesaler
中文
Online consultation
Online map
中
