Electronic – Mobile phone battery charger


I would like to know about the workings of mobile phone battery chargers. I know the basic principle, you take a transformer to bring it down to 9/6/3.7 volts then a bridge rectifier circuit and a capacitor input filter to rectify it into DC. Then you apply it to the battery. But I know this should not be enough, I need at least two things,

  1. Protection against back current flow
  2. Switch off power when the battery is fully charged.

Can someone point me to something simple (apart from this http://www.extremecircuits.net/2009/07/mobile-phone-battery-charger-circuit.html)

Best Answer

You are taking an AC signal from the wall and then as you say, the transformer, recitifier and capacitors are bringing it down to a lower DC voltage. From there, most charging circuits are either linear regulator type chargers or switch mode power supply type regulators (both of those are advanced type links, but just there to see they both exist). They are basically normal DC/DC power converters with some kind of monitoring circuit inside. These two components fulfill the needs you list in number 1 and 2. To learn more about how they work, I'd check out Dave's explanation of linear and switch mode power supplies.

If you're looking to build your own eventually, you'll need to figure out how to do the monitoring with a micro or otherwise and then control some kind of DC/DC power converter. Good luck!