https://www.allaboutcircuits.com/textbook/direct-current/ https://www.allaboutcircuits.com/textbook/direct-current/ this is the one I used, very comprehensive

https://www.allaboutcircuits.com/textbook/direct-current/ https://www.allaboutcircuits.com/textbook/direct-current/ this is the one I used, very comprehensive and useful.