A method for entering and exiting a low power sleep mode in a power converter, said method comprising the steps of: providing a primary-side energy storage circuit comprising a primary-side start-up controller, a power switch coupled to a transformer, and a primary-side energy storage capacitor; providing a secondary-side energy storage circuit comprising a secondary-side controller, and a secondary-side energy storage capacitor; coupling the primary-side and secondary-side energy storage circuits through the transformer; controlling the power switch, during start-up, with the primary-side start-up controller until an operating voltage on the secondary-side energy storage capacitor reaches a desired value; and entering the primary-side controller and the secondary-side controller into a low power sleep mode, wherein the primary-side and secondary-side circuitry, in a low IQ mode, operate from energy stored in their respective energy storage capacitors (250; 244), wherein when a respective voltage on either one of the energy storage capacitors (250; 244) is less than or equal to respective low voltage limits then either the primary-side start-up controller can wake itself or the secondary-side controller can wake itself and the primary-side start-up controller, whereby the primary and secondary energy storage capacitors (250; 244) are charged until both respective voltages are greater than their respective low voltage limits, wherein the secondary-side controller raises a voltage on the secondary-side energy storage capacitor before going into the low power sleep mode and when the voltage on the secondary-side energy storage capacitor rises, a voltage on the primary-side energy storage capacitor also rises, wherein the primary-side start-up controller detects this rise in voltage on the primary-side energy storage capacitor and thereby goes into the low power sleep mode. providing a primary-side energy storage circuit comprising a primary-side start-up controller, a power switch coupled to a transformer, and a primary-side energy storage capacitor; a primary-side start-up controller, a power switch coupled to a transformer, and a primary-side energy storage capacitor; providing a secondary-side energy storage circuit comprising a secondary-side controller, and a secondary-side energy storage capacitor; a secondary-side controller, and a secondary-side energy storage capacitor; coupling the primary-side and secondary-side energy storage circuits through the transformer; controlling the power switch, during start-up, with the primary-side start-up controller until an operating voltage on the secondary-side energy storage capacitor reaches a desired value; and entering the primary-side controller and the secondary-side controller into a low power sleep mode, wherein the primary-side and secondary-side circuitry, in a low IQ mode, operate from energy stored in their respective energy storage capacitors (250; 244), wherein when a respective voltage on either one of the energy storage capacitors (250; 244) is less than or equal to respective low voltage limits then either the primary-side start-up controller can wake itself or the secondary-side controller can wake itself and the primary-side start-up controller, whereby the primary and secondary energy storage capacitors (250; 244) are charged until both respective voltages are greater than their respective low voltage limits, wherein the secondary-side controller raises a voltage on the secondary-side energy storage capacitor before going into the low power sleep mode and when the voltage on the secondary-side energy storage capacitor rises, a voltage on the primary-side energy storage capacitor also rises, wherein the primary-side start-up controller detects this rise in voltage on the primary-side energy storage capacitor and thereby goes into the low power sleep mode.