2.1. Unidirectional use in DC. Used for two-way communication; Unidirectional TVS tube protection devices can only protect against positive or negative pulses, while bidirectional TVS tube protection devices connect one end to the line to be protected and the other end to ground. Both ESD pulses from the reverse and forward directions are released, effectively protecting the IC.

    2.2. TVS transistors can be classified into unidirectional and bidirectional. The forward characteristics of unidirectional TVS transistors are the same as those of ordinary voltage stabilizing diodes, while the hard breakdown at the reverse breakdown inflection point, which is approximately at a right angle, is a typical PN junction avalanche. When there is an instantaneous overvoltage pulse, the current of the device suddenly increases while the reverse voltage rises to the clamping voltage value and remains at this level; The V-I characteristic curve of a bidirectional TVS tube is like a back-to-back combination of two unidirectional TVS, with the same avalanche breakdown and clamping characteristics in both directions. The symmetry relationship between the breakdown voltage on both sides is 0.9 ≤ VBR (positive)/VBR (negative) ≤ 1.1. Once the interference voltage applied at both ends exceeds the clamping voltage Vc, it will be immediately suppressed.

    2.3. Interpolar capacitance Cj

    Unidirectional capacitance is larger than bidirectional capacitance. Taking LRC as an example, unidirectional capacitance C has 65PF, while bidirectional capacitance C only has 15PF;

    2.4. All USB data lines are bidirectional;

    2.5. Different current curves. The circuit symbol of a unidirectional TVS transistor is the same as that of a regular voltage regulator, and its forward characteristic is the same as that of a regular diode, while its reverse characteristic is a typical PN junction avalanche device. Both the forward and reverse directions of bidirectional diodes are typical PN junction avalanche devices.