A power supply, and a method of controlling the power supply, in which more or less power capacity of the power supply is activated depending on the state of a digital data signal on a data bus. The power supply has a control circuit which detects the number of "zero" bits present on the data bus, and responsively activates one or more of a plurality of power supply circuits such as charge pump circuits. The outputs of the charge pump circuits are mutually connected to a driver adapted to program memory cells of a flash memory circuit.