Patent ID: 7710746

Claim:
A switching mode power supply comprising: a power supply unit comprising a switch, coupled to a primary coil at a primary side of a transformer for converting an input DC voltage, configured to supply power to a secondary coil and a tertiary coil at a secondary side of the transformer according to an operation of the switch; a switching controller configured to receive a feedback voltage corresponding to a first voltage generated in the secondary coil at the secondary side of the transformer, to receive a detection signal corresponding to a current flowing through the switch, and to control an on/off operation of the switch by applying a switching control signal to the switch; and a feedback signal generator configured to receive the first voltage and the switching control signal, to sample the first voltage by using a first pulse string, to generate the feedback voltage according to a level of the first voltage sampled according to a first pulse in the first pulse string, to change a toggling time of the first pulse string in a first period for sampling the first voltage, and to change a time for sampling the first voltage.