Transient Limiter helps limit the transients when conducted EMI emissions measured using Line Impedance Stablization Network (LISN).
The RF output port of LISN and the EMI measurement instrument input are coupled to a transient limiter. In order to enable the RF signal to be monitored with an EMC receiver, the Transient LImiter blocks the supply voltage from the LISN RF port while allowing the signal to pass through with little attenuation.
Because the RF signal must be passed through, any short transients (a few microseconds or less) on the power supply lines will also be passed through.
These brief transients are shielded from the EMI receiver input by the transient limiter LIT-153A. Without LIT-153A, an exposed receiver input will be harmed by a transient with sufficient energy.