Patent ID: 6999324
Filing Date: 2006-02-14
Classification: H02M

Abstract:
1. A method for operating a switch connected in series with a primary coil of a transformer in a free-running switch mode power supply, a secondary coil of the transformer being coupled to output terminals carrying an output voltage, the switch being switched on when the primary coil reaches a predetermined magnetization state, which comprises the steps of: applying an input voltage to a series circuit formed by the primary coil and the switch; providing a control signal for controlling power consumption; providing a modulation signal; and providing a drive signal for driving the switch, the drive signal containing a recurrent pulse sequence having at least one first switching-on pulse with a first pulse duration and at least one second switching-on pulse with a second pulse duration, a pulse duration of at least one of the first and second switching-on pulses being modulated by the modulation signal within a range predetermined by the control signal.