The multi-power supply voltage dc/dc converter block according to claim 1, wherein the driving circuit comprises, for each gate of depletion HEMT transistor of the power circuit to be driven, a first depletion HEMT driving transistor, a second depletion HEMT driving transistor, first, second and third resistors, a Schottky diode and an auxiliary power supply voltage, the source of the first driving transistor being connected to the ground, the drain of the first driving transistor being connected to one of the terminals of the first resistor and to one of the terminals of the second resistor, the gate of the first driving transistor being connected to a corresponding input of the driving circuit, the gate of the second driving transistor being connected to the other of the terminals of the first resistor, the source of the second driving transistor being connected to the other of the terminals of the second resistor, to the cathode of the Schottky diode and to one of the terminals of the third resistor, the anode of the Schottky diode being connected to the auxiliary power supply voltage, the other of the terminals of the third resistor being connected to the gate of the corresponding depletion HEMT transistor of the power circuit to be driven, the drain of the second driving transistor being connected to the low power supply voltage when the low power supply voltage is connected to the conduction output terminal of the corresponding depletion HEMT transistor of the power circuit to be driven, or being connected to the corresponding intermediary or high power supply voltage if the intermediary or high power supply voltage is connected to the conduction input terminal of the corresponding depletion HEMT transistor of the power circuit to be driven, the auxiliary power supply voltage being greater than the pinch-off voltage of the second driving transistor, and the low power supply voltage being greater than the auxiliary power supply voltage plus the pinch-off voltage of the corresponding depletion HEMT transistor of the power circuit to be driven.