SWITCHING MODE POWER SUPPLY AND THE DRIVING METHOD THEREOF

摘要

A switching mode power supply and a driving method thereof are provided to reduce an EMI(electromagnetic interference) by maintaining a constant switching frequency modulation range irrespective of an input voltage. A power supply unit(100) includes a switching transistor which is coupled with a primary coil of a transformer. The transformer rectifies an input AC voltage to generate an input DC voltage and changes the input DC voltage. The power supply unit supplies electrical power to a secondary portion of the transformer according to the operation of the switching transistor. A switching controller(400) receives a feedback voltage corresponding to a secondary voltage of the transformer, a sensor signal, and a first signal, and turns on/off the switching transistor. The first signal corresponds to a voltage difference between first and second electrodes of the switching transistor. The switching controller generates a current signal corresponding to the first signal and sets a threshold period, where the current signal is greater than a reference current value. The switching controller turns on the switching transistor during an interval between the threshold period and a variable delay period.