This circuit was obtained in an old Elektor and can be adapted to use white power LEDs. The transistor must be equipped with a heat sink. The circuit has a battery charger.
The circuit in the figure is suggested by ST Microelectronics (www.st.com) and consists of a...
The transistors of this circuit may be the BC548 or BC549 and its power supply can be performed...
This circuit is from Mullard's transistor reference manual from 1960. The circuit will also work...