Patent ID: 8363428

Claim:
An adapter power supply having variable switching mode, the adapter power supply comprising: a switching unit for switching a direct-current (DC) voltage; a transformer including a primary winding connected to the switching unit, a secondary winding electromagnetically coupled to the primary winding, and an auxiliary winding electromagnetically coupled to the primary winding; a rectifier for rectifying a voltage outputted from the transformer; and a controller for controlling the switching unit to operate according to a pulse width modulation (PWM) scheme in a normal operation mode, and to operate according to a quasi-resonant scheme in a standby mode, by detecting information of a load connected to the rectifier, wherein the controller comprises: a current reference generation stage for generating a current reference by comparing an output voltage of the load with a predetermined reference voltage, so as to detect the information of the load; a skip carrier signal generation stage for generating a skip carrier signal; a peak detection stage for detecting a peak value of the skip carrier signal; a first comparison stage for comparing the current reference with the skip carrier signal, thereby determining whether the switching unit is in the normal operation mode or in the standby mode; a second comparison stage for sensing a current flowing through the switching unit, thereby determining a duty of the switching unit through comparison of the current reference with the sensed current; a third comparison stage for comparing the current reference with the peak value of the skip carrier signal, thereby determining which one of the PWM scheme and the quasi-resonant scheme is to be used for operation of the switching unit; a valley detection stage for detecting a valley of a voltage between both ends of the switching unit through the auxiliary winding; a PWM based operation stage connected to the first comparison stage, the second comparison stage, and the third comparison stage, so as to apply a control signal to the switching unit, wherein the control signal allows the switching unit to operate according to the PWM scheme in the normal operation mode; and a quasi-resonant based operation stage connected to the first comparison stage, the second comparison stage, the third comparison stage, and the valley detection stage, so as to apply a control signal to the switching unit, wherein the control signal allows the switching unit to operate according to the quasi-resonant scheme in the standby mode.