Power consumption by the driving circuitry of an output stage, employing a slew-rate controlling operational amplifier, is reduced by modulating the level of the current output by the operational amplifier in function of the working conditions of the output stage. Switching delay may also be effectively reduced. An auxiliary current generator forces an additional current through the conducting one of the pair of input transistors of the operational amplifier only during initial and final phases of a transition, essentially when the slew rate control loop ceases to be effective. The boosting of the bias current through the conducting input transistor is determined by the degree of unbalance of the differential input stage of the operational amplifier, without the use of dissipative sensing elements.