Adding transient voltage suppressor（TVS） transistors to an electric circuit is an important method to protect it from the fast-risetime electromagnetic pulse（FREMP） damage. The package form of the TVS transistors influences the volume

response time

and power consumption of the circuit. However

the influence of the package form on the clamp voltage of TVS transistors affected by FREMP is not considered yet. In this article

the results of the experiment comparing the influence of package form are described

where the rectangular pulses with rise time shorter than 1 ns are used to test protection performance of three different TVS transistors

which have the same framework but different breakdown voltages. The influence of the different package forms on the clamp voltage is analyzed by using the fitting model. It is found that the package form of TVS transistors has less influence on the current characteristics of their protection performance

but more on the voltage characteristics. It is concluded that the diameter or width of the TVS transistors is the main factor determining the clamp voltage. Thus

the diameter or width of the TVS transistors should be big enough to ensure the stabilization of clamp voltage

but

at the same time

fit the allowing volume.