Patent ID: 7684216

Claim:
A switching mode power supply (SMPS) comprising: a power supply block that comprises a first switch coupled to a first coil of a primary side of a transformer for converting an input voltage, wherein the power supply block supplies power to a second coil and a third coil of a secondary side of the transformer according to an operation of the first switch; and a PWM signal generator that receives a feedback voltage corresponding to a first voltage generated in the second coil, a sensing signal corresponding to a current flowing to the first switch, and a third voltage corresponding to a second voltage generated in the third coil to generate a control signal to control on/off of the first switch, wherein the PWM signal generator is configured to determine a turn-on time of the first switch according to the input voltage, and the turn-on time is determined regardless of a power magnitude of an output terminal that is connected to the second coil.