How does the AC-DC power adapter work?

On this page, we clearly explain how AC adapters work. Starting with a description of the circuit, we also explain the names of each component with diagrams. We hope you find this information helpful.

Many electronic devices in the world operate on DC (Direct Current). However, since commercial power is AC (Alternating Current), it must be converted to DC for electronic devices to function. This important task is performed by what is known as an AC adapter. This is why an AC adapter is called an 'AC/DC adapter.'

Due to the trends towards miniaturization, energy efficiency, and simplification of design in electronic devices, products that employ external AC adapters instead of incorporating power supplies internally have been increasing.

Here's what's inside an AC-DC power adapter!

The circuit diagram corresponding to the above photo is as follows.

The roles of each component are explained and introduced in the following order.

1. Power Supply and Fuse

To begin, electricity flows into the AC adapter from your wall outlet through the AC cord. As the current enters the adapter, it first encounters a crucial safety component – the fuse. The fuse serves as a safeguard against overcurrent incidents and equipment damage. In the event of an overcurrent, the fuse will melt, causing the AC adapter to cease operation temporarily.

2. Noise Reduction with Line Filter

Continuing on the journey through the AC adapter, the current passes through a line filter. This component plays a pivotal role in reducing electrical noise, ensuring that the power supply to your devices is as clean and stable as possible.

3. Full-Wave Rectification

The next step involves full-wave rectification, where diodes come into play. Diodes allow the current to flow in only one direction, enabling the adapter to rectify both positive and negative halves of the alternating current (AC) waveform from the wall socket. This process, known as full-wave rectification, aligns the current direction uniformly, resulting in a smoother waveform.

4. Voltage Smoothing with Electrolytic Capacitors

Following rectification, the current enters the realm of electrolytic capacitors. These capacitors store electrical energy and help maintain a consistent voltage. During times of high voltage, they charge up, while during low voltage periods, they discharge, effectively smoothing out voltage fluctuations.

5. Switching for Voltage Regulation

After achieving a smoothed direct current (DC), a transistor is employed to regulate the voltage. The transistor switches on and off, creating high-frequency pulses or square waves. By adjusting the duration of these pulses, the output voltage can be precisely controlled. This switching process allows for the maintenance of a stable output voltage even when the input voltage fluctuates. Additionally, the high-frequency operation enables the use of smaller and lighter transformers, a significant advantage over older transformer-based AC adapters that were bulkier and heavier.

6. Optimal Voltage Conversion with Transformer

The current then passes through a transformer, which optimally converts it to the desired voltage level.

7. Pulse Smoothing with Electrolytic Capacitors (Again)

To further smooth the pulse waveforms created during switching, electrolytic capacitors are employed once more. This process involves multiple iterations, gradually transforming the pulse waves into clean direct current.

8. Noise Reduction with Coils

As the current proceeds, it passes through coils that reduce switching noise, ensuring a cleaner output.

9. Monitoring and Protection

Finally, the AC adapter monitors the output voltage and current, transmitting feedback to the transistor for precise adjustment of the pulse width. This feedback mechanism not only maintains a stable output but also acts as a protective feature. If abnormal voltage or current levels are detected, the AC adapter's protection function will halt its operation, preventing potential damage.

In conclusion, AC adapters are sophisticated devices with multiple components working together to deliver stable and safe power to your electronic devices. Understanding their inner workings can help you appreciate the importance of these components and the role they play in ensuring a reliable power supply.

As described above, each component plays its role in constructing an AC adapter. In addition to the basic structure of AC adapters explained as an example, we are also open to receiving individual requests from our customers for the addition of components or functions. Please feel free to contact us with your specific requirements.

You can get the product catalog in PDF.

Product initiatives

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

See more