Switched mode power supply

A switched mode power supply comprising:

• a reactive element comprising a first terminal, for charging and discharging the reactive element, and a second terminal, for an output voltage;
• a switching stage having a first input and a second input;
• and
• a control signal generator arranged to generate a first control signal at a first output of the control signal generator and a second control signal at a second output of the control signal generator, wherein the first output of the control signal generator is coupled to the first input of the switching stage by means of a first control signal path and the second output of the control signal generator is coupled to the second input of the switching stage by means of a second control signal path;
• wherein the switching stage is arranged to
• (a) during first charging time periods, responsive to the first control signal, couple the reactive element to a first supply voltage for charging the reactive element, and responsive to the second control signal, decouple the reactive element from a second supply voltage lower than the first supply voltage,
• (b) during first discharging time periods, responsive to the first control signal, decouple the reactive element from the first supply voltage, and responsive to the second control signal, couple the reactive element to the second supply voltage for discharging the reactive element, and
• (c) during decoupling time periods, responsive to the first control signal, decouple the reactive element from the first supply voltage, and responsive to the second control signal, decouple the reactive element from the second supply voltage,
• wherein the first charging time periods and the first discharging time periods alternate and are each spaced apart by one of the decoupling time periods;
• a first capacitive element having a first terminal coupled to the first terminal of the reactive element and a second terminal coupled to a first node, wherein the first control signal path is coupled to the first node and is arranged to determine the first drive voltage dependent on a difference between a first node voltage at the first node and a voltage at the first terminal of the reactive element, the first drive voltage being the voltage at which the first control signal is delivered to the first input of the switching stage during the first charging time periods;
• a first charging diode coupled between the first node and a third power supply rail at a third supply voltage higher than the second supply voltage, and arranged for charging the first capacitive element from the third supply voltage;
• a voltage regulator coupled to the first node and to a fourth power supply rail at a fourth supply voltage higher than the third supply voltage, wherein the voltage regulator is arranged to control the first node voltage dependent on the fourth supply voltage;
• a delay detector arranged to generate a delay indicator signal indicative of a relative delay between the first control signal at the first input of the switching stage and the second control signal at the second input of the switching stage;
• and
• an adjustable delay stage in one of the first and second control signal paths and arranged to, responsive to the delay indicator signal, control an adjustable delay so that a first delay experienced by the first control signal passing from the first output of the control signal generator to the first input of the switching stage is substantially equal to a second delay experienced by the second control signal passing from the second output of the control signal generator to the second input of the switching stage.