A switch mode power supply includes a bootstrap circuit, control circuits, and an auxiliary winding coupled to the bootstrap circuit and configured to supply power to the control circuits after startup of the power supply. The bootstrap circuit is configured to supply power to the control circuits during startup and includes an isolation circuit to limit current flow between the starting capacitor and the control circuits while the starting capacitor is charged to a starting voltage by the high voltage input. During the initial charge of the starting capacitor, the control circuits do not have power to provide the initial functionality of the power supply. Once the starting capacitor is charged to the starting voltage, the isolation circuit is activated to allow current flow that powers the control circuits during the remainder of the startup until the auxiliary winding is able to power the control circuits.