Patent ID: 7436642

Claim:
Electronic switch for AC currents, comprising a main bipolar or unipolar switch circuit to switch the AC current from an AC line to a load the main switch circuit including at least a pair of power FET or IGBT transistors for each AC line; a current measurement circuit; a current source circuit comprising, for each pair of transistors, a shunt resistor defining the maximum current (Imax) that the main switch can support, said current source circuit being directly coupled to said main switch and arranged such that when crossed by said maximum current the current source circuit generates a voltage suitable for causing the opening of the main switch; a control logic unit programmable for setting a main switch nominal current value (Inom), a limit current value (Ilim) which is comprised between said main switch nominal current value and said maximum current, a first time interval (Tlim 1 ), a second time interval (Tlim 2 ) and a third time interval (Tlim 3 ), said control logic unit being operable for opening and closing said main switch; a current limiter circuit suitable for comparing the AC current with said nominal current and with said limit current, said current limiter being arranged for sending a corresponding command signal (Ovlow, Ovhgh) to the control logic unit and for directly opening the main switch; wherein, in presence of an inrush current, if said inrush current is higher than the maximum current, a short circuit procedure is activated by the current source circuit, wherein the current source circuit acts to directly open the main switch and activates the control logic unit to trigger said third time interval and to close said main switch circuit at the zero crossing of each cycle of the AC current until said third time interval elapses; if said inrush current is lower than the maximum current but higher than the limit current, a high over-current procedure is activated by the current limiter circuit, wherein the current limiter circuit acts to directly open the main switch and activates the control logic unit to trigger said second time interval and to close said main switch circuit at the zero crossing of each cycle of the AC current until said second time interval elapses; if said inrush current is lower than the limit current but higher than the nominal current, a low over-current procedure is activated by the current limiter circuit, wherein said current limiter circuit activates the logic control unit to trigger said first time interval and to close the main switch until the first time interval elapses, and wherein, in each said procedure, if said inrush current does not decrease below the lower value of the corresponding range before the corresponding time interval elapses, the logic control unit opens the main switch circuit definitively.