AC/DC Power Adapter How does it work?

AC/DC Power Adapter We provide an easy-to-understand explanation of how it works. Starting with an explanation of the circuit, we also explain the names of each component with diagrams, so we hope you will find it helpful.

Many electronic devices operate on DC (direct current). On the other hand, commercial power is AC (alternating current), so unless AC is converted to DC, the devices will not operate. The device that performs this important task is the AC/DC Power Adapter.

This is why it is sometimes called an "AC/DC adapter".

In recent years, due to the miniaturization of electronic devices, energy saving, and simplified design, more and more Products use external AC/DC Power Adapter instead of incorporating a built-in power supply.

The content of this article was also provided as related information when our company offered technical cooperation for the production of NHK's "Chiko-chan ni Shikarareru!" broadcast on April 10, 2026. Click here for details about our cooperation with the NHK program production

Inside the AC/DC Power Adapter

The above photograph can be represented by the following circuit diagram.

Below is a step-by-step explanation of the role of each component.

1. Electricity is supplied to the AC/DC Power Adapter from your wall outlet through an AC cable.
2. The current passes through a fuse.
   *Point: To prevent accidents and equipment damage caused by overcurrent, if excessive current flows, the fuse blows and the adapter stops operating.
3. Noise is reduced by passing through a line filter.
4. Using the property of a diode that allows current to flow in only one direction, both the positive (+) and negative (-) waves of the AC current supplied from the outlet are rectified so that the current flows in the same direction as shown in the figure below (this is called full-wave rectification).
5. Using the charge storage function of an electrolytic capacitor, it charges when the voltage is high and discharges when the voltage is low, smoothing the voltage (reducing fluctuations).
6. After smoothing and converting to DC, a transistor is switched ON/OFF (switching) to generate high-frequency pulses (square waves). By adjusting the ON and OFF time, the output voltage is regulated. Even if the input voltage fluctuates, a stable output voltage can be maintained by adjusting the pulse width. In addition, by using high frequency, the transformer can be made smaller and lighter. (The transformer-type AC/DC Power Adapter that were once mainstream were much larger and heavier compared to switching types.)
7. The transformer converts the voltage to the optimal level.
8. The pulse wave (square wave) is smoothed by an electrolytic capacitor. By repeating this process several times, it is converted into clean DC.
9. It passes through a coil to reduce switching noise.
10. The output voltage and current are monitored and feedback is sent to the transistor to adjust to the optimal pulse width.
    *Point: At this time, if an abnormal voltage or current is detected, it also serves as a protection function that stops operation.

As explained above, each component plays its respective role in constructing the AC/DC Power Adapter.

In addition to the basic structure of the AC/DC Power Adapter explained above, we also accommodate the addition of components or functions according to individual customer requirements, so please feel free to contact us.

Related article: For a basic explanation, please see What is an AC/DC Power Adapter?

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