The surprising complexity inside power adapter


Have you ever wondered what's inside your AC/DC Power adapter?

Let me explain for you:


A diode is a device made with semiconductor material that allows the flow of electricity in one direction. Most diodes have a painted line on one end showing the direction of flow. It has two terminals – anode and cathode. The negative side is normally white.

They are most commonly used to convert AC to DC, because they pass the positive (+) part of the wave, and block the negative (–) part of the AC signal, or, if they are reversed, they pass only the negative part and not the positive part.


A transistor is a three-terminal semiconductor device. It is generally used as a switching device or as an amplifier. It is a combination of two or more Diodes. Transistors are of two types – Bipolar Junction Transistor (BJT) and Field Effect Transistor (FET). They can be PNP (Positive-Negative-Positive) and NPN (Negative-Positive-Positive) transistors.


An inductor is a passive electrical device that introduces inductance into an electric circuit. It is basically a coil of wire with many winding, often wound around a core made of a magnetic material, like iron. The simplest form of an inductor is made up of a coil of wire.


Steps down high voltage AC mains to low voltage AC.

Pico Fuse:

Under normal operation, the fusible alloy is joined by the two lead wires within the housing. When the thermal cutoff senses an abnormal heat and reaches a preset temperature, the fusible alloy melts and disconnects the circuit completely with the aid of the special resin.

Fliter capacitor

we get a pulsating DC output from the rectifier circuit but electronic devices need a constant supply of DC voltage. Because a pulsating DC affects the performance of electronic devices and in some cases, it will not work. To make the constant supply from the rectifier we use filters in power supply circuits.

Schottky Barrier Rectifier Diode:

A:Low forward voltage drop:  The low forward voltage drop offered by Scottky diode power rectifiers is a significant advantage in many applications. It reduces the power losses normally incurred in the rectifier and other diodes used within the power supply. With standard silicon diodes offering the main alternative, their turn on voltage is around 0.6 to 0.7 volts. With Schottky diode rectifiers having a turn on voltage of around 0.2 to 0.3 volts, there is a significant power saving to be gained. However it is necessary to remember that there will also be losses introduced by the resistance of the material, and the voltage drop across the diode will increase with current. The losses of the Schottky diode rectifier will be much less than that of the equivalent silicon rectifier in many applications.

B:Fast switching speeds:  The very fast switch speeds of the Schottky diode rectifier mean that this diode lends itself to use in switching regulator circuits, enabling higher efficiency levels to be achieved than if other types of power rectifier diode had been used.

X capacitor and Y capacitor:

Both the X safety capacitor and Y safety capacitor are safety capacitors. The difference is that the X capacitor is connected across the input line to eliminate the differential mode. The Y capacitor is connected between the input line and the ground line to eliminate common mode.

The X safety capacitor uses a plastic square-shaped high-voltage CBB capacitor. The CBB capacitor not only has better electrical performance but also in parallel with the input of the power supply can effectively reduce the impact of high-frequency pulse on the switching power supply.

Y safety capacitors have high voltage ceramics. The Y safety capacitor is connected between the phase and the ground. In order not to exceed the ground allowable leakage value