Patent ID: 7440296

Claim:
Control circuit for controlling the output voltage of a primary-controlled switched-mode power supply, wherein the switched-mode power supply comprises a primary-side switch and a transformer with at least one auxiliary winding, in which an auxiliary voltage is induced after opening the primary-side switch, wherein the control circuit is adapted to set the switching frequency of the primary-side switch in a linear relationship to a measurement voltage produced from the auxiliary voltage, wherein a constant factor of this linear relationship is selected such that the output current of the switched-mode power supply assumes a predetermined value, wherein the control circuit comprises a measurement voltage terminal for connection to the measurement voltage and a supply voltage terminal, separate from same, for connecting to a supply voltage which is produced from the auxiliary voltage,and wherein the control circuit is formed such that it compares the voltage dropped across a charging capacitor with a reference value and produces a turn-on siginal for switching on the primary-side switch when the voltage dropped across the charging capacitor reaches the reference value that can be set in relationship to the measurement voltage.