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Better LM317 based battery charger. This improved version implements the CCCV charging method. There are a lot of variations of this circuit out there. Some incorporate LED indicators or adjustable charging output voltages.
Like in my last circuit, I'm trying to use a capacitor to simulate a battery cell. Flip the switch to charge / discharge the "battery."
The CCCV (Constant Current Constant Voltage) method is the recommended way to charge lithium batteries. First, a constant current charges the battery (in this case, the blue waveform or 200mA). This current keeps flowing until the battery voltage rises close to full. Then, it changes states to hold the voltage constant (in this case, the green waveform or 4.15V) and let the current slowly trickle down. The battery is then fully charged.
Honestly, I don't really have a full grasp of how this circuit works. But I think the main idea is that the 3.3Ω resistor is used to set the charging current, and the other resistors set the final charge voltage. The transistor helps switch states when the battery voltage gets close to full. But, I really don't know for sure. If you can help explain it better. please leave a comment.
LM317 Series:
Adjustable Voltage Regulator: https://everycircuit.com/circuit/6138847104335872
Constant Current Source: https://everycircuit.com/circuit/5424946364547072
Adjustable Current Source: https://everycircuit.com/circuit/4902539157569536
Soft Power On: https://everycircuit.com/circuit/6070007032971264
Simple Battery Charger: https://everycircuit.com/circuit/4594156412076032
Linear Power Supply: https://everycircuit.com/circuit/6413550326906880
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