US Patent 7889522 Flyback switching power supply and control method thereof

A flyback switching power supply capable of regulating an operation frequency based on a current regulation mechanism is disclosed. The flyback switching power supply includes a transformer, a switch, a switch control circuit, and a regulation circuit. The transformer includes a primary winding for receiving an input voltage, a secondary winding for generating an output voltage, and an auxiliary winding. The switch is serially connected to the primary winding for controlling a current flowing through the primary winding. The switch control circuit has a frequency control port and functions to work around an operation frequency for controlling the switch. The operation frequency is under control by a frequency setting current flowing through the frequency control port. The regulation circuit is electrically coupled between the auxiliary winding and the frequency control port. The regulation circuit adjusts the frequency setting current based on an induced current generated by the auxiliary winding.