^{Careful friends will find that since the birth of the mobile phone, the mobile phone has become thinner and lighter, and the size of the mobile phone charger is getting smaller and smaller. So how is this technically achieved?}

^{Previous chargers used a linear regulated power supply, usually requiring a bulky transformer, first dropping the voltage of 220V and then charging the circuit with a transistor. Since the operating frequency of this transformer is 50 Hz, the transformer must have sufficient inductive reactance, which means that it is bulky. Therefore, the volume of the previous charger is mainly limited by the transformer, and the previous transistor and the resistive container are relatively large in volume, which also accounts for the volume.}

^{The current charger adopts switching power supply technology, which can directly rectify 220V, then cut or turn on the rectified voltage at a certain frequency to obtain an approximate square wave signal, and finally obtain a stable low voltage by using negative feedback and smoothing filtering. The source eliminates the bulky transformer. Of course, the switching power supply also has a transformer. However, since the switching frequency of the switching power supply is much higher than 50 Hz, the required transformer inductance is small, and the volume of the transformer can be made small. In addition, the current devices are miniaturized, and the circuit can be made small.}