Zener Diode in parallel with TVS Diode

[zjynus]

Dear Experts,

I have a question regarding TVS diode and Zener Diode.

From what I read from internet or books, TVS diodes are specifically designed, characterized and tested for transient voltage suppression; while Zener diodes are designed towards voltage regulation. After conducting a simple simulation in LTSpice, I found TVS diodes can also do voltage regulation and Zener Diodes can suppress voltage spike as well. Can anyone please share any experience with TVS or Zener diodes? What are the differences between them?

In one product schematic, I found the following connection. My question is, why there are both Zener Diode and TVS diode in this circuit? Only Zener Diode or Only TVS Diode will be enough to protect the circuit, is it? Please correct me if I am wrong. A little bit more about the diagram below:
- D1 is a Zener Diode with breakdown voltage of 130V
- D2 is a TVS diode with clamping voltage of 136V
- Normally, Power supply provides 100V DC voltage. AC voltage/voltage spikes are possible to occur in power supply under certain condition.

Any ideas/suggestions/comments are welcome! Thank you!

 

[chuckey]

try this :- https://en.wikipedia.org/wiki/Transient-voltage-suppression_diode In the references at the end of the article there is a good training paper from Littlefuse. Just because someone has used this configuration does not mean its the optimum one. Some times there is a speed/power problem where one device is very fast but is only rated to handle the power until the second device comes on which is slower but can handle far more power.
Frank

 

[crutschow]

TVS's are rated for high peak power and current, since they are designed to suppress high energy transients. Zeners are not rated for such applications (although they may indeed work for that).

 

[zjynus]

try this :- https://en.wikipedia.org/wiki/Transient-voltage-suppression_diode In the references at the end of the article there is a good training paper from Littlefuse. Just because someone has used this configuration does not mean its the optimum one. Some times there is a speed/power problem where one device is very fast but is only rated to handle the power until the second device comes on which is slower but can handle far more power.
Frank

Frank, thanks!

I found this point very useful, "Some times there is a speed/power problem where one device is very fast but is only rated to handle the power until the second device comes on which is slower but can handle far more power".

Does that mean, when there is a voltage spike which lasts for a short period of time, TVS can handle it; when the overvoltage lasts for a long time, TVS cannot handle it but Zener can do voltage regulation under this condition?

Please correct me if I am wrong. Thanks a lot!

Jessie

 

[FvM]

Some times there is a speed/power problem where one device is very fast but is only rated to handle the power until the second device comes on which is slower but can handle far more power.

That's an important point in circuit protection, but doesn't particularly apply to parallel circuits of TVS and "regular" zener diodes. They have quite similar dynamical behaviour and even the energy absorption capability of a TVS and a power zener diode won't be very different. As crutschow said, the main difference is that they are specified differently.

This also implies, that a parallel circuit of both devices doesn't make much sense because exact limiting voltage as well as energy share would be undefined. A combination in a staggered protection concept with a current limiting means inbetween may be reasonable.