The use of the battery has been more than one hundred years. The performance of the battery directly affects the service life and safety of the electronic product, and the performance of the charger directly affects the performance of the battery. Most of the traditional chargers are composed of power frequency transformers and rectifier circuits (SCR phasing). Although the circuit is extremely simple, there are many disadvantages that cannot be ignored: bulky, poor reliability, low charging efficiency, manual duty during charging, and constant Adjust the charging current and so on. The intelligent fast charger designed in this paper is charged according to the charging characteristic curve of the battery. It has the functions of fast charging, high reduction efficiency, no over-charging danger, and automatic end charging, which solves the above problems and improves the quality and efficiency of charging. The charging methods of batteries at home and abroad mainly include constant current, constant voltage, constant voltage current limiting, pulse charging, and Relfex charging method. The system uses the high-frequency chip SG3525AN as the core to generate a PWM pulse of about 9 kHz, using a three-stage charging method. The so-called three-stage charging method specifically refers to a constant current charging phase, a constant voltage charging phase, and a trickle charging phase (also called a floating charging phase). (1) Constant current charging phase. During the constant current charging phase, the charging current remains the same, but the output voltage is changing. The circuit automatically adjusts the output voltage based on the charge current to keep the current at a constant stage. On the one hand, when the current increases, the circuit automatically reduces the output voltage, so that the current decreases and remains constant; on the other hand, as the battery power increases, the voltage across it increases continuously, in order to prevent the charging current from becoming smaller. The output voltage of the switching power supply must gradually rise with the charging process. The current at this stage is large. The value of the charging current is determined according to the following formula: Charging current (A) = battery capacity (Ah) & TImes; 1.2 (efficiency) & TImes; 8 (h) Where: 1.2 efficiency is a fixed value; 8h refers to the standard charging time. (2) Constant voltage charging phase. The constant voltage charging phase means that when the voltage of the battery rises to a set constant voltage value, the output voltage of the switching power supply remains unchanged, and the charging current decreases according to the charging condition of the battery. The charging voltage value is calculated as follows: Constant voltage charging voltage (V) = battery cell voltage (V) & TImes; battery cell number (pieces) (3) Trickle charging phase. The trickle charging phase means that when the battery is substantially full, the circuit automatically reduces the output voltage of the switching power supply according to the detected charging current. At this time, the output voltage is stable and the current continues to decrease, and the charging ends after about 2 hours. The curve of the three-stage charging is shown in Figure 1. Figure 1 Three-stage charging curve Motor Start Switch,Single Phase Motor Starter Switches,Single Phase Centrifugal-Switches,Electric Machine Centrifugal Switch Gear Ningbo Zhenhai Rongda Electrical Appliance Co., Ltd. , https://www.centrifugalswitch.com