Lithium battery charger

 
I. Design Background
This charging module project originated from a classmate's Zhengdian Atom drone, which required frequent and lengthy charging cycles. This sparked the idea of ​​creating a charger. Additionally, I'm planning to build a five-person drone for fun, and the battery power supply is a good first step.
II. Design Summary
Lithium batteries have specific charging rules; the charging current cannot exceed 0.5-1.5 times the battery capacity. My primary rechargeable battery capacity is no more than 500mAh, typically around 300-400mAh. Therefore, the TP4059 is a suitable choice:
• Reverse polarity protection for lithium batteries; • Programmable charging current up to 600mA;
• Constant current/constant voltage operation with thermal regulation to maximize charging rate without overheating; • Direct charging of single lithium-ion batteries from a USB port; • 4.2V preset charging voltage accuracy of ±1%; • Maximum input voltage up to 9V;
VI. Hardware Circuit Composition
 
The hardware circuit mainly consists of four TP4059 chips, several filter capacitors, indicator LEDs, current setting resistors, and current limiting resistors. It offers three charging current settings: 300mAh, 500mAh, and 600mAh. The main circuit principle is shown in the diagram below.
VIII. Physical Demonstration
IX. Precautions
The main thing to note is the battery's positive and negative terminals; avoid problems at the connection points. Although there is reverse connection protection, please note that if the battery already has a voltage greater than 4V, it will not enter the charging state when you try to charge it.