Current flowing through an inductor on a primary side of a voltage converter is sensed and compared to a threshold peak current value to determine when to end an ON portion of the voltage converter. The secondary side of the voltage converter supplies an indication of output voltage for use in determining the threshold peak current value. On start-up the primary side detects when the indication of output voltage is supplied by the secondary side across on isolation channel. Prior to detecting the indicating is being supplied, the primary side uses an increasing threshold peak current as the threshold peak current value. After detection that the indication of output voltage is being provided by the secondary side, the threshold peak current value is based on the indication of the output voltage.