A DC-DC boost converter comprises a charge pump selectively operating in a voltage doubler or in a voltage tripler mode. A switching arrangement connects the charge pump to an input voltage terminal in a charge phase and to an output voltage terminal in a discharge phase. A controllable current source is connected in series with the charge pump in the discharge phase and an error amplifier has a first input connected to a reference voltage, a second input connected to the output voltage terminal and an output connected to a control input of the controllable current source. The converter further comprises a mode changeover circuit with a first comparator having a first input connected to the output of the error amplifier and a second input connected to a first threshold voltage source. A second comparator has a first input connected to the output of the error amplifier and a second input connected to a second threshold voltage source. A flip-flop has its set input connected to the output of the first comparator, its reset input connected to the output of the second comparator. The flip-flop has its output connected to the switch arrangement to switch the charge pump from doubler mode to tripler mode when the voltage at the output of the error amplifier exceeds the second threshold voltage and back to doubler mode when the output voltage at the error amplifier drops below the first threshold voltage.