What is the structure of an AC adapter?

On this page we will explain the construction of an 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 direct current (DC). On the other hand, the most common commercial current is alternating current (AC), so if you do not convert AC to DC, most electronic equipment will not operate. It is the AC adapter that makes this possible.

In recent years, products that use AC adapters are increasing in number and built for miniaturization of electronic equipment, power saving, and design simplification.

Inside an AC adapter.

The above picture is a circuit diagram.

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

Electricity is also supplied to the AC adapter from AC outlet.
The current passes through the fuse.
* Note: To avoid accidents caused by overcurrent and the destruction of equipment, if an overcurrent occurs, the fuse blows and the operation of the adapter stops.
Through a line filter to reduce noise.
By flowing current only in one direction through the diode, both positive and negative waves of the alternating current supplied from the socket are rectified, and the flow direction is as shown in the following figure, (i.e. full-wave rectification).

By storing the electricity in the electrolytic capacitor, it charges when the voltage is high, discharges when the voltage is low, and smooths the voltage (reduces fluctuation).
After being smoothed into direct current, the electricity is turned on/off (switching) with a transistor and made into a high frequency pulse (rectangular wave). The output voltage is adjusted by adjusting the timing. 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. Thus, we can reduce the weight of the product. (The transformer type AC adapter, which was once mainstream, was very heavy compared with the switching type.)
Converted to optimum voltage with a transformer.
The pulse wave (rectangular wave) is smoothed by the electrolytic capacitor. By repeating this several times, it will be made into a clean direct current.
It passes through the coil and switching noise is reduced.
The output voltage and current are monitored and transmitted to the transistor to adjust it to the optimum pulse width.
* Note: While detecting an abnormal voltage/current, the transformer also plays the role of a protection function that stops operation.

As explained above, each part plays their respective role and in total constitutes an AC adapter.

In addition to an AC adapter with the basic structure explained previously as an example, we also accept 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 rigorous quality controls.