Patent ID: 7518836

Claim:
A switching mode power supply comprising: a power supply including a main switch coupled to a primary coil of a transformer, operable to supply power to a secondary coil of the transformer according to an operation of the main switch; a feedback circuit, operable to generate feedback information corresponding to an output voltage, output by an output unit including the secondary coil of the transformer; and a switching controller, operable to receive current sensing information on the current flowing through the main switch and the feedback information through a single terminal; and to perform a protection operation when the voltage at the single terminal is maintained below a reference voltage for more than a first time period, wherein the switching controller comprises: a comparator, operable to compare the voltage at the single terminal and the reference voltage, to output a first signal level when the voltage at the single terminal is lower than the reference voltage, and to output a second signal level when the voltage at the single terminal is higher than the reference voltage; a D flipflop, operable to receive an output of the comparator through a data terminal, and to receive clock signals through a clock signal terminal; a counter, operable to receive an output of the D flipflop through an enable terminal, and to count the time during which the input signal is in the enable state; and a protection circuit, operable to receive information on the counted time from the counter, and performing a protection operation when the counted time is greater than a second time.