This invention relates to driver circuits used within high voltage power supplies, e.g. for light bulb assemblies. A driver circuit providing electrical energy at an output derived from electrical energy at an input is described. The driver circuit comprises a power converter, a controller, a supply voltage capacitor, and is configured to provide a supply voltage to the controller. A start-up resistor is coupled to the input of the driver circuit, charges the supply voltage capacitor, and is coupled to the supply voltage capacitor during start-up of the driver circuit. A back-up capacitor is coupled to the output of the driver circuit and with the supply voltage capacitor if a voltage at the back-up capacitor exceeds the supply voltage by a forward voltage threshold, and is decoupled from the supply voltage capacitor if the supply voltage exceeds the voltage at the back-up capacitor by a reverse voltage threshold.