electronic_hobbyist
Newbie level 2
I am trying to design a lithium-ion battery charger for a single battery 3.7v, 2500mAh. I will be charging the battery using CC/CV method with a constant charge current of 0.5C or 1250mA and CV of 4.2V. I will be using an LM317 and the charging configuration from the datasheet. An Arduino will monitor the battery voltage and switch between the modes. According to my simulation, my CV mode is working, but my CC mode isn't. I am using the configuration as per CC mode 1 and my input voltage to the LM317 is 12V whereas, the regulated output voltage is 7V with a constant current of 1250mA. The output voltage of 7V is beyond the 4.2V required for the lithium battery, and this will damage it. I am thinking about using CC Mode 2 as per the attachment with a constant current of 1250mA and voltage of 3V which will increase to 4.2V as the battery charges. Would this work? I will also like to use a high pass transistor to pass the majority of the current around the LM317 because my LM317 will need a large heatsink. How can I create a circuit using a pass transistor to pass 1000mA and send 250mA through the LM317?