In one embodiment, a circuit couples an integrated circuit to a powerline and protects the integrated circuit from overvoltage noise. In one example, the integrated circuit comprises a two-port differential transceiver. Respective Schottky diodes couple the ports to a power supply and reference, so one diode for each port conducts current in forward bias if an applied voltage exceeds a respective voltage reference plus the forward voltage of that diode. A respective end of a first transformer winding feeds each input port. Respective ends of a second transformer winding couple to capacitors that couple with the powerline. Back-to-back zener diodes are connected between the ends of the second winding. A zener diode with a breakdown voltage set based on the power supply voltage plus a margin is coupled between the power supply and ground so that the power supply voltage does not exceed a desired value plus the margin.