A charge pump can be used with a bus-powered device connected to a bus. The charge pump is formed of a power connection from the bus carrying a DC power signal constrained to not exceed a given current limit and a given voltage limit, a DC-to-DC step-down voltage converter, a capacitor, and a DC-to-DC step-up voltage converter. The step-down converter has an input connected to the power connection and produces an intermediate signal having a voltage the same or less than the voltage of the power signal. The capacitor is connected to the output of the step-down converter. The step-up converter has an input connected to the output of the step-down converter and to the capacitor, and produces a final output signal having a voltage greater than the given voltage limit. The output of the step-up converter is connected to and provides DC power to the device.