How do AC/DC Power Adapters — Desktop & Wall-Mount work?

We provide a clear explanation of how AC/DC power adapters — desktop & wall-mount work. Starting with circuit descriptions, each component is illustrated and explained with diagrams, so we hope you find it helpful.

Many electronic devices operate on DC (direct current). However, since commercial electricity is AC (alternating current), these devices won’t function unless AC is converted to DC. That’s exactly the important role played by AC/DC Power Adapters — Desktop & Wall-Mount.

This is why they are sometimes referred to as "AC/DC adapters."

In recent years, more and more products are using AC/DC Power Adapters — Desktop & Wall-Mount instead of integrating power supplies internally, due to miniaturization, energy efficiency, and simplified design.

We present the inside of an AC/DC Power Adapter — Desktop & Wall-Mount.

The schematic diagram of the photo above is shown below.

Internal circuit diagram of AC/DC Power Adapters — Desktop & Wall-Mount

We will now explain and introduce the roles of each component in turn.

  1. Electricity is supplied to the AC/DC Power Adapter — Desktop & Wall-Mount through an AC cord from a wall outlet.
  2. The current passes through a fuse.
    Note: To avoid accidents and equipment damage caused by overcurrent, the fuse melts and stops the adapter from working if excessive current flows through it.
  3. A line filter reduces noise.
  4. Using the property of a diode that only allows current to flow in one direction, both the positive and negative waveforms of the AC current from the outlet are rectified so that their flow direction becomes the same as shown in the diagram below (this is called full-wave rectification).Diagram of AC current flow
  5. Using the charging and discharging property of an electrolytic capacitor, it charges when voltage is high and discharges when it’s low, smoothing out voltage fluctuations.Diagram of smoothed voltage
  6. After smoothing and converting to DC, a transistor switches it on and off to create a high-frequency pulse (square wave). The output voltage is adjusted by controlling the ON/OFF timing. Even if the input voltage fluctuates, a stable output voltage can be maintained by adjusting the pulse width. Also, high frequency allows the transformer to be more compact and lightweight. (The transformer-based AC/DC Power Adapters — Desktop & Wall-Mount, which used to be common, were much larger and heavier compared to switching types.)Diagram of voltage converted to high-frequency pulse
  7. The transformer converts the voltage to an optimal level.
  8. An electrolytic capacitor smooths the pulse wave (square wave). This process is repeated several times to produce clean DC.Diagram of smoothed pulse wave and clean DC
  9. The current passes through a coil, reducing switching noise.
  10. The output voltage and current are monitored and fed back to the transistor to adjust the pulse width optimally.
    Note: This also functions as a protection feature that stops operation if abnormal voltage or current is detected.

As described above, each component performs its own role in constructing the AC/DC Power Adapter — Desktop & Wall-Mount.

While the example above explains a basic structure, our company also supports customized components or features to meet individual customer requirements. Please feel free to contact us.

Related article: For a basic overview, please see What is an AC/DC Power Adapter — Desktop & Wall-Mount?

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