Here is the indicative schematic circuit diagram of the usb charger doctor, drawn by me. Voltage measured at various points, when powered by my lab power supply (dialed to 5.0 Vdc), is also included ...

Here is a tried and tested sample circuit of a Li-Ion battery charger that can be used to charge any 3.7V Li-Ion battery using a 5VDC (USB, Solar Panel…) power supply. At the heart of the circuit is ...