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I'm new in the subject and cannot figure out how to use TVS for a particular reason.

Here is what I commonly see TVS at the input of a circuit:

enter image description here

Here another circuit has TVS again at the input, but this time with a resistor before:

enter image description here

So should the topology be: Input signal -->TVS or Input signal-->Resistor-->TVS ?

EDIT:

Please see the difference? Which one is appropriate? I found the diagrams from this question.

With resistor:

enter image description here

Without resistor:

enter image description here

Edit 2:

What should be the rule of thumb when sizing TVS? Let me ask with an example:

For example I don't want voltage transients to the input of an opamp exceed 12V. And if I use this TVS, would it be proper?

Below are the specs for the TVS:

enter image description here

Regarding the specs and my 12V limitation which condition should be satisfied:

Maximum Breakdown Voltage > 12V ?

Minimum Clamping Voltage > 12V ?

GNZ
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  • This is a interesting question, but: How can someone answer without knowing what you're designing? That's like asking if you should buy a car or truck...totally depends on what you're using it for. Please state what you are trying to protect, and what kind of input signals you expect to have. – Bort Sep 03 '17 at 13:30
  • Oh so it depends? But if we dont use resistor wont a huge current flow through TVS during a transient? – GNZ Sep 03 '17 at 13:32
  • depends, can the electronics under normal conditions operate satisfactory with said impedance in series? –  Sep 03 '17 at 13:32
  • I added two examples to my question – GNZ Sep 03 '17 at 13:37
  • @HezarFen - I'm assuming you want the TVS to protect something right? Would you rather that current go through the rest of your circuit? TVS diodes are often used to protect from things like static discharge, where the current will be very temporary. – Bort Sep 03 '17 at 13:37
  • What are you protecting? A power line? A signal input? – ThreePhaseEel Sep 03 '17 at 13:38
  • @HezarFen - You could replace that input resistor with a fuse if you are worried about large currents flowing through the TVS. That way the normal operation is (probably) not effected, and if the TVS shorts to ground with enough current, the fuse will open and no current will flow. – Bort Sep 03 '17 at 13:39
  • Yes but sometimes a resistor is before TVS to limt current sometimes not – GNZ Sep 03 '17 at 13:39
  • @ThreePhaseEel I want to protect the circuit – GNZ Sep 03 '17 at 13:40
  • @Bort Thanks how about a MOV before TVS ? – GNZ Sep 03 '17 at 13:41
  • Please see my Edit 2, which parameter should be considered when sizing the TVS? I tried to explain this question in the last edit. – GNZ Sep 03 '17 at 15:04

0 Answers0