Battery Charger circuit for mobile phones. It consists of a rectifier circuit which converts AC to DC. Then it is feeded to a zener diode which limits this voltage to around 14V. As the rectifier output is in pulses, base of the transistor connected to its line gets fired in pulses and hence flow of current through zener diode to resistors and then to capacitor takes place.
Once the capacitor fully charged with voltage of 14V, voltage across zener and capacitor becomes equal and hence no current flows through base of transistor. As a result, transistor goes cutoff and eventually there is no further overcharging.
MODIFIED : Turn on the gate switch and get almost pure DC Output.
