A circuit for providing input surge protection in a digital input module, the circuit comprising a surge protection input stage, including a bridge rectifier coupled to receive the bidirectional input signal, and coupled to the unidirectional input of the digital input module. The bridge rectifier comprises TVS rectifiers TVS1 and TVS2, and diode rectifiers D2 and D3, intercoupled in a bridge rectifier configuration in which: TVS1 and TVS4 are transient voltage suppression diodes; and rectifiers D2 and D3 are rectifier diodes. Diodes TVS1 and TVS4 can be implemented as either respective unidirectional TVS diodes; or a single bidirectional TVS diode. The digital input module can be a digital input receiver, or a opto-isolator/coupler, or other digital input module.