In the initial start-up period of power converter, there is no voltage supply from auxiliary winding to pulse-width-modulation (PWM) IC. Therefore, a typical method is connected with a start-up resistor (R_start) between bridge rectifier and IC controller for initial voltage supply. However, the R_start would continue to consume energy even if the auxiliary voltage has been set up. The proposed scheme uses depletion-type NMOS to connect with R_start. The start-up mechanism can be guaranteed without any additional voltage, and naturally cut off the R_start to minimize power dissipation once the voltage of PWM IC is supplied from auxiliary winding. As a result, the outstanding standby power performance can be implemented and comply the power regulation of 5 star standards of mobile charger. Experimental results demonstrate the standby power consumption only 28.8 mW.