This laptop power adapter circuit is designed using TOP269EG off-line switcher IC, (U1), used in a flyback configuration.
TOP269EG IC has an integrated 725 V MOSFET and a multi-mode controller. It regulates the output by adjusting the MOSFET duty cycle, based on the current fed into its CONTROL pin.
This 15v variable power supply electronic project is designed using 2N3055 transistors. Output voltage of this variable power supply can be adjusted in the range between 1.5 and 15 volts. This 2N3055 15v variable power supply can provide a maximum current of 500 mA. Stabilization is better than 2%, if the currents do not exceed 350 mA.