A switched mode power supply for converting an input voltage into a DC output voltage and comprising: an inductor arranged in series with a series arrangement of a power switch, comprising a bipolar junction transistor, and a control switch, the control switch connected to an emitter terminal of the power switch for controlling the power switch, the inductor arranged for connection to a load; a controller configured to control the control switch and having a supply terminal and a ground terminal; a capacitor coupled between the controller ground terminal and supply terminal and for providing power to the controller; a first current path between the emitter terminal of the power switch and the supply terminal of the capacitor, the first current path comprising a diode and arranged to provide a base charge of the bipolar junction transistor to the capacitor, said charge being provided by the first current path only when the control switch is open and the power switch is closed; a connectable second current path between the control, base terminal of the power switch and the supply terminal of the capacitor, and arranged to draw current from the control terminal of the power switch thereby opening the power switch wherein the current drawn from the control terminal of the power switch is provided by a base charge of the bipolar junction transistor in an on-state, and a connection switch configured to connect the second current path in response to a voltage across the capacitor exceeding a threshold voltage; a further current path from the supply terminal of the capacitor to the central base terminal of the power switch and including a resistor; and wherein the controller is configured to open and close the control switch, wherein closing of the control switch is configured to close the power switch via the emitter terminal and thereby cause the current in the control switch, the power switch and inductor to rise, wherein the further current path is arranged to provide current to the base terminal at start-up and wherein opening of the control switch provides the base charge to the capacitor through the first current path, when the diode starts conducting, causing the voltage across the capacitor to rise and wherein when the voltage exceeds the threshold voltage, the connection switch is closed and the base charge is conducted to the capacitor by the second current path thereby discharging the base terminal and opening the power switch. an inductor arranged in series with a series arrangement of a power switch, comprising a bipolar junction transistor, and a control switch, the control switch connected to an emitter terminal of the power switch for controlling the power switch, the inductor arranged for connection to a load; a controller configured to control the control switch and having a supply terminal and a ground terminal; a capacitor coupled between the controller ground terminal and supply terminal and for providing power to the controller; a first current path between the emitter terminal of the power switch and the supply terminal of the capacitor, the first current path comprising a diode and arranged to provide a base charge of the bipolar junction transistor to the capacitor, said charge being provided by the first current path only when the control switch is open and the power switch is closed; a connectable second current path between the control, base terminal of the power switch and the supply terminal of the capacitor, and arranged to draw current from the control terminal of the power switch thereby opening the power switch wherein the current drawn from the control terminal of the power switch is provided by a base charge of the bipolar junction transistor in an on-state, and a connection switch configured to connect the second current path in response to a voltage across the capacitor exceeding a threshold voltage; a further current path from the supply terminal of the capacitor to the central base terminal of the power switch and including a resistor; and wherein the controller is configured to open and close the control switch, wherein closing of the control switch is configured to close the power switch via the emitter terminal and thereby cause the current in the control switch, the power switch and inductor to rise, wherein the further current path is arranged to provide current to the base terminal at start-up and wherein opening of the control switch provides the base charge to the capacitor through the first current path, when the diode starts conducting, causing the voltage across the capacitor to rise and wherein when the voltage exceeds the threshold voltage, the connection switch is closed and the base charge is conducted to the capacitor by the second current path thereby discharging the base terminal and opening the power switch.