Patent ID: 7391629

Claim:
A switching mode power supply (SMPS) comprising: a power supply having a main switch coupled to a primary coil of a transformer, and supplying power to a secondary coil of the transformer according to an operation of the main switch; a feedback circuit for generating a feedback voltage corresponding to an output voltage at the secondary coil; and a switching controller comprising: a normal operation circuit for comparing the feedback voltage to a first voltage corresponding to a current flowing through the main switch, and generating a first control signal for controlling the duty of the main switch; and an overcurrent operation circuit for comparing a predetermined voltage with the first voltage and generating a second control signal for controlling the duty of the main switch, wherein the overcurrent operation circuit has a circuit delay which is shorter than that of the normal operation circuits, wherein a source of the predetermined voltage is configured to generate the predetermined voltage during an initial startup to start from a second voltage, gradually rise at a rate not determined by a rise of a supply voltage, and level off at a third voltage.