First power supply circuit is built with BD139, one zener diode and a few passive components. Each of the schematic is very simple to construct and will function without problems if you respect the ...

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 ...