Show off your own DIY single-chip multi-function charger

I saw someone discussing chargers a few days ago. Since I had nothing to do, I decided to show off my own DIY charger design!

This is the circuit diagram when it was first designed. Later, during the specific debugging process, it was found that the MOS tube and inductor in the BUCK generated very high heat. When I looked at the waveform, I found that the waveform that was supposed to be a square wave had become a triangle wave!

I spent a lot of time, checked a lot of information, and did experiments, and found that the MOS tube was not driven well. It was not enough to drive it with a single transistor (probably because my tube was fake and the input capacitance was too large). Later, I had to change to using a 667/647 complementary output circuit to drive it.

Sure enough, the waveform of the MOS tube driver was much better, but the heat was still severe, and the waveform of the inductor input was still very bad, and it was still hot. I looked for the reason again, and later thought that the inductor might be saturated (originally, it used a black ordinary magnetic core, and one circle had an inductance of 20UH), so I used 26-grade magnetic core to wrap 74 circles to reach 330UH, and finally it was not saturated! When the output current was more than 3 amperes, it still would not be saturated. Finally, the output wave formed a perfect square wave, and the output ripple was much smaller. The MOS tube generated very little heat, and the inductor was not hot!

I used AVR MEGA16 microcontroller, 16K FLASH/1K SRAM/512BIT EEPROM, and used four ADCs as current and voltage sampling for two charging channels. TIMER1 used A/B two-way output 28KHZ PWM waveform to control two BUCK circuits to control voltage and current.

Use 5V-30V DC power supply, 2 IRF9540 for BUCK, 330UH inductor is wound by toroidal core. According to my own calculation, 3A DC can be passed when the inductance drops to 70%, so the actual BUCK waveform is still very good (very neat square wave) when the current is large, and the loss of the BUCK part is very small. According to the input voltage, this BUCK can control a wide range of voltage and current.

The program is written by myself, and it can charge NiMH batteries, storage batteries, and lithium batteries. Through the serial port of MAX232, the charging time, charging current, charging voltage and other information can be observed in real time on the PC. When discharging, the final discharge ampere-hour can also be seen after calculation.