Patent ID: 6608769
Filing Date: 2003-08-19
Classification: H02M

Abstract:
A switched mode power supply comprising:a flyback converter comprising a first input line and a second input line, both of which are connected to input voltage source during use; output terminals to supply an output voltage; a capacitor connected between the output terminals; a Schottky diode connected in reverse direction between the output terminals in parallel with the capacitor to prevent output voltage from increasing above a threshold value; a transformer having a primary winding; a first controllable switching device having a control input and having a main current path; a current measuring resistor, wherein the primary winding, the main current path of the first controllable switching device and the current measuring resistor form a series arrangement having one end connected to the first input line and a second end connected to the second input line; and a second controllable switching device having a control input and having a main current path that connects the control input of the first controllable switching device to one of the first and second input lines, wherein the second controllable switching device has a conductivity that depends on a voltage residing at its control input, which voltage is influenced by first, second, and third control voltages, and wherein the first control voltage increases in response to an increase in the current flowing through the current measuring resistor, the second control voltage is producible from the input voltage by a primary voltage divider and increases in response to an increase in the input voltage, and the third control voltage increases in response to an increase in the output voltage.