How should the surge protection circuit for the AC power input port of a ventilator be designed?

A multi-stage coordinated protection architecture based on gas discharge tubes (GDTs) and metal oxide varistors (MOVs) must be adopted. The first stage of protection uses an MOV with a high current-handling capacity, directly connected in parallel between the line and neutral wires, to absorb most of the surge energy and provide initial voltage clamping. The second stage of protection employs a GDT, connected in series after the MOV or as common-mode protection between the lines and ground. It responds slightly slower but can withstand higher surge currents, providing backup protection for the preceding stage and ensuring sufficiently low residual voltage. Appropriate decoupling inductors or resistors should be incorporated between the two stages to achieve graded energy dissipation. Ultimately, this ensures that the residual voltage entering the subsequent DC/DC power module remains below its withstand level, meeting the test level requirements of standards such as IEC 61000-4-5.