Homemade USB interface powered mobile phone battery charger circuit diagram

The charging current of this circuit has two levels to choose from: 100mA (when switch SB is open in the picture) and 500mA (when switch S is closed in the picture). When pin 1 of the MAX1811 allowed by the circuit is connected as shown in the figure, the maximum charging voltage is 4.2V; when pin 1 is connected to the negative terminal of the power supply, the maximum charging voltage is 4.1V. Once the maximum charging voltage is reached, the charging current decreases sharply and the maximum charging voltage remains unchanged. In the figure, VD1 is used as the power indicator, and VD2 is used as the charging indicator. The light is on to indicate charging, and the light is off to indicate the end of charging.