A synchronous converter for driving a load, the synchronous converter comprising: a first switch coupled in series with a second switch via a node (x); an inductor coupled to the node (x); input terminals (10, 11) for receiving an input voltage from a power source; output terminals (12, 13) for supplying an output current and an output voltage to the load; wherein the synchronous converter is arranged to be operated in a first mode and a second mode, wherein in the first mode the first switch is in an on state and the second switch is in an off state; and wherein in the second mode the first switch is in the off state and the second switch is in the on state; and wherein the synchronous converter further comprises a control circuit, the control circuit comprising: a threshold control circuit for generating a threshold control signal for switching off the first switch when a current threshold of a current through this switch is exceeded, wherein the threshold control circuit has an input for receiving a current signal indicating a current through the switch (M1, M2), and a comparator for comparing the current signal with the current threshold to obtain the threshold control signal; characterized in that the control circuit further comprises an on-time control circuit comprising a calculating unit for directly calculating an on-time duration for the second switch, wherein the on-time duration is proportional to the product of the inductance value and twice the sum of the average output current (Iled) and a desired negative peak current (Ineg) and inversely proportional to the output voltage (Vout) when the first switch and the second switch are coupled between the input terminals (10, 11), or to the difference between the output voltage (Vout) and the input voltage (Vin) when the first switch and the second switch are coupled between the output terminals (12, 13), wherein the control circuit is adapted for adjusting the negative peak current (Ineg) and a positive peak current (Ipos) to obtain a constant switching frequency of the synchronous converter during dimming of the load. a first switch coupled in series with a second switch via a node (x); an inductor coupled to the node (x); input terminals (10, 11) for receiving an input voltage from a power source; output terminals (12, 13) for supplying an output current and an output voltage to the load; wherein the synchronous converter is arranged to be operated in a first mode and a second mode, wherein in the first mode the first switch is in an on state and the second switch is in an off state; and wherein in the second mode the first switch is in the off state and the second switch is in the on state; and wherein the synchronous converter further comprises a control circuit, the control circuit comprising: a threshold control circuit for generating a threshold control signal for switching off the first switch when a current threshold of a current through this switch is exceeded, wherein the threshold control circuit has an input for receiving a current signal indicating a current through the switch (M1, M2), and a comparator for comparing the current signal with the current threshold to obtain the threshold control signal; characterized in that the control circuit further comprises an on-time control circuit comprising a calculating unit for directly calculating an on-time duration for the second switch, wherein the on-time duration is proportional to the product of the inductance value and twice the sum of the average output current (Iled) and a desired negative peak current (Ineg) and inversely proportional to the output voltage (Vout) when the first switch and the second switch are coupled between the input terminals (10, 11), or to the difference between the output voltage (Vout) and the input voltage (Vin) when the first switch and the second switch are coupled between the output terminals (12, 13), wherein the control circuit is adapted for adjusting the negative peak current (Ineg) and a positive peak current (Ipos) to obtain a constant switching frequency of the synchronous converter during dimming of the load. a threshold control circuit for generating a threshold control signal for switching off the first switch when a current threshold of a current through this switch is exceeded, wherein the threshold control circuit has an input for receiving a current signal indicating a current through the switch (M1, M2), and a comparator for comparing the current signal with the current threshold to obtain the threshold control signal; characterized in that the control circuit further comprises an on-time control circuit comprising a calculating unit for directly calculating an on-time duration for the second switch, wherein the on-time duration is proportional to the product of the inductance value and twice the sum of the average output current (Iled) and a desired negative peak current (Ineg) and inversely proportional to the output voltage (Vout) when the first switch and the second switch are coupled between the input terminals (10, 11), or to the difference between the output voltage (Vout) and the input voltage (Vin) when the first switch and the second switch are coupled between the output terminals (12, 13), wherein the control circuit is adapted for adjusting the negative peak current (Ineg) and a positive peak current (Ipos) to obtain a constant switching frequency of the synchronous converter during dimming of the load.