in general , an increase or a decrease of the number of active phases in a multi - phase system , as already said , is determined in an adaptive manner to deliver output current , for optimizing the efficiency of the system at different load currents . clearly the number of active phases that the voltage regulator system has at steady state conditions of operation is determined by its output current . therefore , the output current of any multi - phase voltage regulator system is monitored . generally , the output current information is read from a common current sense circuital arrangement and the information is compared with a number of thresholds in order to determine the band of output current values within which the power supply system is functioning . these thresholds should be programmable because the number of phases that should be made active in function of the current depends on the specific application , the type of power mosfets used , the switching frequency and other regulation parameters . a typical example of a circuit adapted to monitor the band of output current in which the voltage regulator is working is depicted in fig3 . the current imon represents the output current of the regulator read by a common current sensor and represents the sum , suitably scaled , of the currents flowing in the active phases ph 1 , ph 2 , . . . , phn . the circuit of fig3 includes a resistor rmon for converting the output current into a voltage signal v mon . the circuit includes comparators comp 2 , comp 3 , . . . , compn that are configured to compare the voltage signal v mon to a plurality of threshold voltages v 2 xi , v 3 xi and vnxi , respectively , which are proportional to the threshold currents for passing from 1 - to - 2 phases , 2 - to - 3 phases and 3 - to - 4 phases , respectively . the circuit also includes a capacitor cmon which is a common filter capacitor for suppressing switching noise on the output voltage and / or for reducing the ripple present on the imon signal . the comparators each have an hysteresis representing the difference of threshold between passages from 1 - to - 2 and from 2 - to - 1 and so forth in order to avoid repeated triggerings of the comparator upon reaching a triggering threshold . fig4 shows an example of timing of the signals of adaptive management of the number of activated phases of a three phases system , according to a common technique . the vmon signal represents the output current information of the multi - phase power supply system . when the vmon signal surpasses the threshold v 2 xi , the output of the corresponding comparator rises . when vmon surpasses also the threshold v 3 xi , also the output of the comparator comp 2 rises . a reverse mechanism applies when the output current decreases , apart from the hysteresis of the comparators . commonly , the output logic value of the comparators are combined together through a simple combinatory logic circuit in order to generate the target number of phases ph_cur , coherent with the current information . a digital embodiment of the current mode control scheme as shown in fig5 is also possible . assuming that the output current value is converted to a digital datum by an adc 10 , it is possible to program digital threshold values ( preferably with a certain hysteresis ) and obtain the same information on the band of current levels of the current being delivered by the supply voltage regulator . in particular , a phase shedding logic block 12 can be used to generate the target number of phases ph_cur as already said , this information on the band of values in which the output current being delivered is insufficient for establishing the number of phases that should be activated . in particular , during a load transient , the vmon information does not represent the load requirement because the voltage regulator hasn &# 39 ; t yet responded to the transient . supposing that the voltage vmon is below the threshold value v 2 xi , the voltage regulator functions with only one active phase . if , in this condition of operation , a load increase transient takes place , the system would be subjected to a considerable drop of the output voltage . this disclosure provides an outstandingly effective remedy to this inconvenience by preventing the drop of output voltage that would otherwise occur because of the load transient , by instantaneously incrementing the number of active phases of the system . a possible analog embodiment of a circuit for instantaneously incrementing the number of active phases of the system is depicted in fig6 . referring to the basic circuit diagram of the figure , ifreq is a current proportional to the nominal switching frequency ( that is the switching frequency programmed by the multi - phase system ). cfreq is a capacitance sized in a way that the voltage on it rises by a certain quantity v 1 xt in a time equal to the nominal switching period tsw . the circuit of fig6 also includes a switch 14 , controlled by a signal ck_trigger , and a set of comparators comp 2 f , comp 3 f , . . . , compnf . the voltages v 2 xf , v 3 xf and vnfx may be obtained from a common divider ½ , ⅓ , . . . 1 / n of the voltage v 1 xf . ck_trigger is a signal that , at system level , commands the switching on of a phase . under static conditions of operation , the frequency of this signal is equal to n * fsw , where n represents the number of the phases . by eliminating the cfreq information at every beat of the ck_trigger signal , it is possible to measure in which band of frequency the voltage regulator is functioning . in fig7 a sample timing diagram for a generic three phase system is depicted . at every beat of ck_trigger , the voltage on the capacitance cfreq , called freq check ramp , is made equal to zero by the switch 14 . the capacitance integrates the ifreq current proportional to the nominal frequency programmed by the system . when the voltage on the capacitance cfreq surpasses the v 3 xf threshold , it means that the instantaneous system frequency is less than 3 * fsw . when the voltage surpasses also the v 2 x threshold , it means that the instantaneous system frequency is less than 2 * fsw . is thus possible , at every clock beat , to store the state of the comparators comp 2 f , comp 3 f , . . . , compnf , and determine the band of switching frequency at which the system is operating . at this point , two pieces of information are available : the target number of phases that is determined by the current information ph_cur , and also the number of phases as determined by the information on the instantaneous switching frequency ph_freq . in fig8 an alternative digital embodiment ( typically of lesser cost than an analog embodiment ) is schematically depicted , according to which the calculation of the duration of the real switching period tsw real is carried out by a simple counter 16 which receives a clock and the ck_trigger signal . the block tsw_eq_thr generator is a threshold generator 18 that generates the threshold tsw_eq_thr below which the system of switching on again available phases should intervene . in practice it will be tsw_eq_thr = tsw_nominal /( nph + 1 ). the digital comparator 20 compares tsw real and the threshold tsw_eq_thr and generates as output the command add_1_ph , that can be handled by a logic circuit block pwm / interleaving 22 as a command for adding a phase to those already active . according to a first embodiment the decisional flow for determining the number of phases to be kept on may be as depicted in fig9 . in this example of decision flow , ph_on represents the number of phases to be kept on , ph_freq represents the current number of active phases according to the frequency control loop of the constant - on - time system being considered , ph_cur represents the target number of phases according to the output current control , cnt represents a generic counter and delay represents a programmable delay ( it may be also zero ) for which the system , once having incremented the number of active phases , waits for the counter cnt reach a certain delay , before eventually intervening to decrement anew the number of active phases . in step 24 , the method determines whether ph_freq or ph_cur is greater than ph_on . if so , then in step 26 the method sets ph_on to the maximum of ph_freq and ph_cur and sets cnt to zero . if neither ph_freq nor ph_cur is greater than ph_on , then the method determines whether cnt equals delay in step 28 . if not , then cnt is incremented in step 30 and the method returns to step 24 . if cnt equals delay , then in step 32 the method sets ph_on equal to ph_cur . according to an alternative embodiment , the decision flow for determining the number of phases to be kept active , according to which the number of phases is incremented by one phase at the time ( stepwise ) may be as illustrated in fig1 . the steps of the method of fig1 are the same as the method of fig9 except that step 26 is replaced with step 34 which increments ph_on by one rather than changing ph_on to the maximum of ph_freq and ph_cur . fig1 is a representation of the inputs / outputs of a logic circuitry block 36 adapted to manage the number of active phases upon changes of the electrical load , according to a digital embodiment of this disclosure . fig1 reproduces oscillographs of signal waveforms that illustrate the behavior of the novel system of re - activation of stand - by phases of the multi - phase power supply system , realized in digital form . the various embodiments described above can be combined to provide further embodiments . these and other changes can be made to the embodiments in light of the above - detailed description . in general , in the following claims , the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims , but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled . accordingly , the claims are not limited by the disclosure .