What is the structure of the AC adapter?

On this page we will explain the mechanism of the AC adapter in an easy-to-understand manner. Beginning with the explanation of the circuit, we will explain the names of each part by illustration for easier reference.

Many electronic devices operate with DC (direct current). On the other hand, the commercial current is AC (AC), so if you do not convert AC to DC, the equipment will not move. It is the AC adapter that does the hard work.

In recent years, products that use AC adapters are increasing without making the power source part built for miniaturization of electronic equipment, power saving, and design simplification.

inside of the AC adapter.

If the above picture is circuit diagram, it becomes as follows.

We will explain and explain the role of each part in order below.

  1. Electricity is also supplied to the AC adapter from AC outlet by AC outlet.
  2. The current passes through the fuse.
    * Points: To avoid accidents caused by overcurrent and destruction of the equipment, if an overcurrent flows during passing, the fuse blows and the adapter operation stops.
  3. Through a line filter to reduce noise.
  4. By using the function of flowing current only in one direction of the diode, both positive (plus) and negative (minus) waves of the alternating current supplied from the socket are rectified, and the flow direction is as shown in the following figure I will do the same. (Full-wave rectification is called)

  1. By utilizing the function of storing the electricity of the electrolytic capacitor, it charges when the voltage is high, discharges when the voltage is low, and smoothes the voltage (reduces fluctuation). 
  2. After being smoothed into direct current, turn it on / off (switching) with a transistor and make it a high frequency pulse (rectangular wave). Adjust the output voltage by adjusting ON and OFF time. Even when the input voltage fluctuates, it is possible to maintain stable output voltage by adjusting the pulse width. Also, by making it high frequency, the transformer is also small. We can reduce weight. (The transformer type AC adapter, which was once mainstream, was very heavy compared with the switching method.)
  3. Convert to optimum voltage with transformer.
  4. The pulse wave (rectangular wave) is smoothed by the electrolytic capacitor. By repeating this several times, It will make it a clean direct current.
  5. It passes through the coil and reduces switching noise.
  6. It monitors the output voltage and current and transmits it to the transistor to adjust it to the optimum pulse width.
  7. * Points: When detecting an abnormal voltage / current at this time, it also plays the role of a protection function that stops operation.

As explained above, each part plays the role of each and constitutes an AC adapter.

In addition to the AC adapter with the basic structure explained as an example, we are also accepting the addition of parts or functions according to individual requests from customers, so please do not hesitate to contact us.

You can get the product catalog in PDF.

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Since 1989, UNIFIVE has maintained the quality of their AC power adapters and switching power supplies through a rigorous quality,

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