An integrated circuit, comprising: a bias supply input for receiving power from a bias supply circuit coupled to an auxiliary winding of an isolated converter; a bias supply output for supplying power to an isolated converter switch controller arranged to control a switch (Q L1) coupled to a primary winding (Np) of said isolated converter; a bias power regulator circuit connected between the bias supply input node and the bias supply output node, wherein the bias power regulator circuit comprises a boost switch, and wherein the bias power regulator circuit is configured to provide a bias supply output voltage to the bias supply output node based on modulating a switching frequency of the boost switch if a voltage level at the bias supply input node is not greater than a bias supply input threshold, and based on using a forward path with the boost switch off if the voltage level at the bias supply input node is greater than the bias supply input threshold, wherein the bias power regulator circuit comprises: modulation circuitry configured to provide a plurality of modulation modes to modulate the switching frequency of the boost switch; and a mode controller configured to receive a light load signal and to select one of the plurality of modulation modes; wherein one of the plurality of modulation modes is a) a constant off-time modulation mode, and wherein the mode controller is configured to select the constant off-time modulation mode when the light load signal indicates that an isolated converter load condition is lighter than a load threshold and while a bias supply input voltage at the bias supply input node is less than the bias supply input threshold; or b) a constant peak-current modulation mode, and wherein the mode controller is configured to select the constant peak-current modulation mode when the light load signal indicates that while an isolated converter load condition is not lighter than a load threshold and a bias supply input voltage at the bias supply input node is less than the bias supply input threshold. a bias supply input for receiving power from a bias supply circuit coupled to an auxiliary winding of an isolated converter; a bias supply output for supplying power to an isolated converter switch controller arranged to control a switch (Q L1) coupled to a primary winding (Np) of said isolated converter; a bias power regulator circuit connected between the bias supply input node and the bias supply output node, wherein the bias power regulator circuit comprises a boost switch, and wherein the bias power regulator circuit is configured to provide a bias supply output voltage to the bias supply output node based on modulating a switching frequency of the boost switch if a voltage level at the bias supply input node is not greater than a bias supply input threshold, and based on using a forward path with the boost switch off if the voltage level at the bias supply input node is greater than the bias supply input threshold, wherein the bias power regulator circuit comprises: modulation circuitry configured to provide a plurality of modulation modes to modulate the switching frequency of the boost switch; and a mode controller configured to receive a light load signal and to select one of the plurality of modulation modes; wherein one of the plurality of modulation modes is a) a constant off-time modulation mode, and wherein the mode controller is configured to select the constant off-time modulation mode when the light load signal indicates that an isolated converter load condition is lighter than a load threshold and while a bias supply input voltage at the bias supply input node is less than the bias supply input threshold; or b) a constant peak-current modulation mode, and wherein the mode controller is configured to select the constant peak-current modulation mode when the light load signal indicates that while an isolated converter load condition is not lighter than a load threshold and a bias supply input voltage at the bias supply input node is less than the bias supply input threshold. modulation circuitry configured to provide a plurality of modulation modes to modulate the switching frequency of the boost switch; and a mode controller configured to receive a light load signal and to select one of the plurality of modulation modes; wherein one of the plurality of modulation modes is a) a constant off-time modulation mode, and wherein the mode controller is configured to select the constant off-time modulation mode when the light load signal indicates that an isolated converter load condition is lighter than a load threshold and while a bias supply input voltage at the bias supply input node is less than the bias supply input threshold; or b) a constant peak-current modulation mode, and wherein the mode controller is configured to select the constant peak-current modulation mode when the light load signal indicates that while an isolated converter load condition is not lighter than a load threshold and a bias supply input voltage at the bias supply input node is less than the bias supply input threshold.