Shown on this slide is an example of a basic overvoltage and overcurrent protection scheme used for a typical port. The TBU® High-Speed Protector (HSP) is placed in series to limit the I/O current. The placement of a T Series Fast Acting GDT (OVP2) on the external port protects the TBU® HSP and the circuit from excessive voltage after the TBU® HSP operates - for the duration of the lightning surge. The T Series Fast Acting GDT is designed to operate at an impulse voltage less than the maximum operating voltage (Vimp) of the TBU® HSP thus protecting it from damage. While the OVP2 device may provide minimum ESD protection for the TBU® HSP, the OVP1 device (usually a small TVS diode) sets the overvoltage protection threshold for the system. The OVP1 device can provide ESD protection to the downstream circuit but it can also be incorporated in the protected circuit. Applications where the protected signal line also delivers power (AC or DC) will require more sophisticated engineering.