When we look at the specification sheet of TVS diodes, we often come across the following two types of pin function identification diagrams.：

For beginners, seeing this might cause confusion. Are they the same? What are the differences? Why do some have two pointed ends pointing outward and the anodes connected together, while others have two pointed ends pointing inward and the cathodes connected together? Three questions in a row. EMC guy made a brief analysis based on his own experience. 

Both the specifications for these two types of diagrams indicate "bidirectional ESD protection diode". Therefore, it can be determined that the functions of these two types are the same, both being bidirectional protection diodes. 

Figure 1 is more commonly seen in the specification sheets of foreign brands, such as Nexperia (Anshihua), Littelfuse (American Littelfuse), VISHAY (Vishay), etc. Figure 2 shows that domestic brands are more frequently used, such as Shanghai Leumo. 

Let's look at the application of two types of TVS diodes in circuits: refer to Figures 3 and 4.

Now, let's look at Figure 3: After the static electricity arrives, it first reversely breaks through the diode connected to pin 1 through D1, then positively passes through the diode connected to pin 2 below D1 (subtracting approximately 0.7V), and finally is introduced to the ground. 

Figure 4: After the static electricity arrives, it first passes through the upper connection of D2 above the first diode (subtracting approximately 0.7V), then breaks down and passes through the diode connected to the second terminal of D2, and finally is introduced to the ground. 

Therefore, after the static electricity enters, both types of TVS diodes need to undergo a reverse breakdown and forward conduction voltage before being discharged to the ground. So, from an electrical performance perspective, the functions achieved by these two types are the same, and there is no difference in application. 

So are there any fundamental differences between them? We know that a diode is composed of a PN junction, as shown in Figure 5. Current flows from the P terminal into the N terminal and then out. It conducts in the forward direction. The forward voltage drop of a silicon diode, VF, is 0.7 volts.

For TVS diodes, since they function as a reverse breakdown protection mechanism, current flows from the N terminal to the P terminal, and from the P terminal to the N terminal is the forward conduction. 

Then, the internal structures of the two TVS diode functional diagrams shown in Figures 1 and 2 can be approximately represented as follows:

This is the reason for the difference in the internal layered structure of these two types of diodes. 

Therefore, from the perspective of electrical characteristics, both Figure 1 and Figure 2 show bidirectional TVS diodes. There is no difference in application, only the internal structure varies. For engineers, as long as the parameters in the device specification book are similar and the functions achieved are the same, the two can be considered interchangeable. 

Shanghai Leiditech, leveraging its years of technological accumulation, offers its domestic ESD/TVS components that can be compatible and substitute for products from multiple foreign brands such as NXP, SEMTECH, LITTELFUSE, ON, VISHAY, and TI. The company provides circuit protection solutions in areas like USB interfaces, automotive electronics, and industrial control, and has a detailed list of alternative models for reference. Leiditech products support sample applications, helping customers optimize their supply chains and achieve domestic substitution. 

Leiditech Electronics is committed to becoming a leading brand in electromagnetic compatibility solutions and component supply, offering products such as ESD, TVS, TSS, GDT, MOV, MOSFET, Zener, and inductors. Leiditech has an experienced R&D team that can provide personalized customization services based on customer needs, offering the best solutions to customers.