An apparatus comprising: a switch configured to operate in a receive mode and a protection mode, wherein the resistance of the switch is substantially constant in the receive mode, and wherein the switch may operate as a constant current source in the protection mode, wherein the switch comprises first and second NMOS transistors (M1A, M2A) whose source terminals are coupled together; and a voltage detection circuit coupled to the switch that is configured to measure a potential difference between two terminals (SWA, SWB) of the switch, wherein the two terminals (SWA, SWB) correspond to respective drain terminals of the first and second NMOS transistors (M1A, M2A); the apparatus further comprising a third transistor and a fourth transistor configured to turn the switch off depending on the output of the voltage detection circuit, in order to switch it from receive mode to protection mode; wherein source terminals of the third and fourth transistors (M6, M7) are coupled to the source terminals of the first and second NMOS transistors (M1A, M2A); wherein drain terminals of the third and fourth transistors (M6, M7) are coupled one to the other and are coupled to gate terminals of the first and second NMOS transistors (M1A, M2A); wherein the switch and the voltage detection circuit do not include any depletion mode devices; wherein the voltage detection circuit comprises first and second rheostats (R1, R2) configured to measure the potential difference between the two terminals (SWA, SWB) of the switch, the first rheostat being coupled between the source terminal and the drain terminal of the first NMOS transistor and the second rheostat being coupled between the source terminal and the drain terminal of the second NMOS transistor; and wherein a gate terminal of the third transistor is coupled to the middle terminal of the first rheostat, and a gate terminal of the fourth transistor is coupled to the middle terminal of the second rheostat. a switch configured to operate in a receive mode and a protection mode, wherein the resistance of the switch is substantially constant in the receive mode, and wherein the switch may operate as a constant current source in the protection mode, wherein the switch comprises first and second NMOS transistors (M1A, M2A) whose source terminals are coupled together; and a voltage detection circuit coupled to the switch that is configured to measure a potential difference between two terminals (SWA, SWB) of the switch, wherein the two terminals (SWA, SWB) correspond to respective drain terminals of the first and second NMOS transistors (M1A, M2A); the apparatus further comprising a third transistor and a fourth transistor configured to turn the switch off depending on the output of the voltage detection circuit, in order to switch it from receive mode to protection mode; wherein source terminals of the third and fourth transistors (M6, M7) are coupled to the source terminals of the first and second NMOS transistors (M1A, M2A); wherein drain terminals of the third and fourth transistors (M6, M7) are coupled one to the other and are coupled to gate terminals of the first and second NMOS transistors (M1A, M2A); wherein the switch and the voltage detection circuit do not include any depletion mode devices; wherein the voltage detection circuit comprises first and second rheostats (R1, R2) configured to measure the potential difference between the two terminals (SWA, SWB) of the switch, the first rheostat being coupled between the source terminal and the drain terminal of the first NMOS transistor and the second rheostat being coupled between the source terminal and the drain terminal of the second NMOS transistor; and wherein a gate terminal of the third transistor is coupled to the middle terminal of the first rheostat, and a gate terminal of the fourth transistor is coupled to the middle terminal of the second rheostat.