The workflow is roughly as follows: When connected to the Li+ battery and the power supply, the IC detects the battery voltage through the network composed of R1/R2/R3. If the battery voltage is lower than 3.3V (determined by the resistance value of R1-R3), or press Press SW1, and the voltage of IC3 pin is lower than 615mV, then IC4 pin outputs low level, pulls the gate of Q1 low through R5/D2, and turns on the battery through Q1/R9/D1 Charging, when the battery voltage rises all the way up to 4.20V, at this time, the IC's 1 pin voltage is higher than 615mV, the IC internally judges and delays, so that the 4 pin outputs a high level, thus turning off the large current charging channel, but 4 feet The high level simultaneously supplies power to the R7/C2 charging loop, causing the gate voltage to Q3 to rise slowly, and providing a path to R8 to cause Q2 to conduct, and R10 provides a weaker on-current to Q1. It is slightly turned on to provide a less supplemental charging current to the battery. According to the component parameters shown in the figure, after about ten minutes, due to the continuous charging of C2, the terminal voltage, that is, the gate voltage of Q3, rises until Q3 is turned on, thereby turning off Q2, so that the entire charging process ends.
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