A high-efficiency digital voltage controller capable of providing monotonically-varying stepwise voltage, said controller comprises of a plurality of two-terminal voltage modules connected in series; within each module one or more two-terminal voltage cells of identical voltage each and connected in series; within each module a plurality of switches controllable to connect any number of the voltage cells in series to the output terminals of the voltage module; the ratios of the magnitudes of voltage of any one voltage cell between the voltage modules being substantially equal to integer values uniquely defined by present invention, according to the numbers of voltage cells in each of the voltage modules; said plurality of switches being controlled by a control module implemented in any suitable logic.