Primary controlled switched-mode power supply comprising: a control circuit for controlling the output voltage of the primary-controlled switched-mode power supply, a primary-side switch and a transformer with at least one auxiliary winding (114, 116), in which an auxiliary voltage is induced after opening the primary-side switch, and a charging capacitor which is connected with an input terminal (Ct) of the control circuit, wherein the charging capacitor can be charged in relationship to a measurement voltage (V) generated from said auxiliary voltage, wherein the control circuit is adapted to set the switching frequency of the primary-side switch in a linear relationship to the measurement voltage, by the voltage dropped across the charging capacitor controlling the switching frequency of the primary-side switch, and wherein a constant factor of this linear relationship is selected such that the output current (I AUS) of the switched-mode power supply assumes a predetermined current value, and wherein the control circuit is adapted to compare the voltage dropped across the charging capacitor with a reference value (V(Ct-Ref)) and produces a turn-on signal for switching on the primary-side switch when the voltage dropped across the charging capacitor reaches the reference value, wherein the control circuit comprises a measurement voltage terminal for connection to the measurement voltage (V) and a supply voltage terminal (V P), separate from same, for connecting to a supply voltage (V) which is produced from the auxiliary voltage, and wherein the control circuit is formed such that it short-circuits the charging capacitor when the measurement voltage (V) reaches a predetermined voltage value, and wherein the reference value (V(Ct-Ref)) can be adjusted depending on the measurement voltage (V). a control circuit for controlling the output voltage of the primary-controlled switched-mode power supply, a primary-side switch and a transformer with at least one auxiliary winding (114, 116), in which an auxiliary voltage is induced after opening the primary-side switch, and a charging capacitor which is connected with an input terminal (Ct) of the control circuit, wherein the charging capacitor can be charged in relationship to a measurement voltage (V) generated from said auxiliary voltage, wherein the control circuit is adapted to set the switching frequency of the primary-side switch in a linear relationship to the measurement voltage, by the voltage dropped across the charging capacitor controlling the switching frequency of the primary-side switch, and wherein a constant factor of this linear relationship is selected such that the output current (I AUS) of the switched-mode power supply assumes a predetermined current value, and wherein the control circuit is adapted to compare the voltage dropped across the charging capacitor with a reference value (V(Ct-Ref)) and produces a turn-on signal for switching on the primary-side switch when the voltage dropped across the charging capacitor reaches the reference value, wherein the control circuit comprises a measurement voltage terminal for connection to the measurement voltage (V) and a supply voltage terminal (V P), separate from same, for connecting to a supply voltage (V) which is produced from the auxiliary voltage, and wherein the control circuit is formed such that it short-circuits the charging capacitor when the measurement voltage (V) reaches a predetermined voltage value, and wherein the reference value (V(Ct-Ref)) can be adjusted depending on the measurement voltage (V).