How to select a TVS diode?

Moderator's note: This is a continuation of http://forum.allaboutcircuits.com/threads/how-to-select-a-tvs-diode.61072/#post-1050992z

ke5nnt said:

From what I'm gathering from your information is:

Working voltage is normal operation where the TVS does not conduct (spare for a specified leakage current). I should select a TVS diode that has a working voltage about equal (or slightly higher) to what I expect max normal voltage will be (about 16V in my case).

Breakdown voltage is the point where avalanche breakdown begins to occur. The device shouldn't reach this point EXCEPT in some type of load spike from a transient which will be very brief and is handled by the clamping voltage. Normal operation above the breakdown voltage can cause overheating of the TVS and TVS failure.

Clamping voltage is set to be just below max circuit damage voltage (below 30V for my case) and stops a transient from damaging the circuit (in theory).

Does it sound like I'm on the right track? Thanks for the feedback.

Click to expand...

Sry for waking up a zombie thread but I did not understand, was this method confirmed ?

I'd also understand that the TVS working voltage (Vrwm) should be the voltage that you expect the circuit to work on (so below maximum operating voltages of devices on protected rail). In my case this would be up to 4.5V.

Breakdown (Vbr) voltage should be the voltage when you expect the diode to start conducting - thus wasting exess energy. In my case the absolute maximum ratings of the devices on protected rail. One device is 6V max VCC (some can go up to 10V).

Clamping voltage would be the voltage drop on the TVS with certain current (since I have seen no graph in any datasheets of how the current relates to this clamping, and I would never experience these high currents, i currently don't worry about it).

BUT I can't find any TVS that meets these requirements. For an example: I wouldn't use TVS with 3.0V working voltage on 4.5V rail to meet 6V breakdown voltage requirement... Choosing f.i. 5V TVS, its breakdown is too high to protect absolute maximum requirement of the device.
I thought to use MMBZ6V8AL but breakdown is above 6V.

How would one proceed in such case (which seems to happen more often than it seems)?

(Again sry for waking up an old topic, but this bugs me a lot).