in a multi - phase power supply voltage regulator functioning at a nominal switching frequency , one or more phases are kept off for optimizing energy efficiency at relatively low load conditions . reactivation of stand - by phases in response to a load increase transient is made more efficiently by exploiting information already present in the output voltage control loop . the technique comprises a ) deriving from the control loop information on the equivalent nominal switching frequency given by the product of the nominal switching frequency by the number of active phases ; b ) updating at every beat of a clock signal the instantaneous value of the equivalent switching frequency ; c ) determining the band of equivalent switching frequency values to which the instantaneous value belongs ; d ) logically combining the equivalent switching frequency information with a determined band of output current level , for switching on one or more stand - by phases in response to a load increase transient .