Connect with us

Testing A TVS Diode

Discussion in 'General Electronics Discussion' started by Sadlercomfort, Feb 29, 2016.

  1. Sadlercomfort

    Sadlercomfort Ash

    424
    53
    Feb 9, 2013
    Hi Guys,

    Is it appropriate to test a TVS diode using a diode check, and simply testing both ways.

    I have a smbj33 TVS Diode which is used between the +/- of a motor in a H-Bridge Circuit.

    I'm getting 0.121V and 0.194V each way. :cool:

    Thanks,
    Ash
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,230
    1,861
    Nov 17, 2011
    Consider a TVS as a special kind of zener diode which is designed to absorb comparatively high energy pulses within a short time. Therefore:
    • yes, you can check the forward direction (conducting) with the diode check of a multimeter.
    • no, you can't check the backward direction completely. You can check that the TVS is not conducting at low voltages (therefore I'd say your measurement indicates a defec TVS). To check the breakdown voltage you need a higher voltage source with appropriate current limiting.
    Did you check the diode in circuit? Remember to de-solder one leg for this kind of test, otherwise you will measure other circuit elements, too (e.g. the motor's resistance, the body diodes in MOSFET transistors etc.)
     
  3. Sadlercomfort

    Sadlercomfort Ash

    424
    53
    Feb 9, 2013
    Right, the TVS diode is SMT so I tested it in-ciruit.

    It's also showing less than 200Ω one side and around 50Ω the other.
    If i test a known good one, also in-circuit i get like 0.65MΩ each side.

    So shall i continue to desolder with a hot-air gun.. and re-test?
     
  4. Sadlercomfort

    Sadlercomfort Ash

    424
    53
    Feb 9, 2013
    Okay, the low resistance is due to the faulty mosfets which were damaged during a fault, they have shorted.

    I removed the TVS diode and tested using a diode check and got nothing, I tested resistance and got an infinite resistance.

    I removed two known good TVS diodes and tested them.. i got the same thing.
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    9,230
    1,861
    Nov 17, 2011
    That's the most meaningful approach, although the comparative measurements youmade indicate that the low-Ω TVS is very probably defect.
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    9,230
    1,861
    Nov 17, 2011
    So the culprit is obviously the MOSFET, not the TVS.
     
  7. Sadlercomfort

    Sadlercomfort Ash

    424
    53
    Feb 9, 2013
    Is it too late to mention.. I was trying to find what caused the MOSFETS to short?

    I had already tested two of the FETs and found they had shorted.. the cause of this is important.
    I also tested several other components in the H-Bridge Circuit and found no faults.

    I assumed the TVS diode was the cause of the fault, but didn't know how to test this.
     
  8. Sadlercomfort

    Sadlercomfort Ash

    424
    53
    Feb 9, 2013
    So I've tested the TVS diode and two other known good ones, and have
    the same measurements so how do I know if the diode is the faulty?

    You mentioned testing the breakdown voltage of the diode with a high voltage source.. How would i setup this test?

    I have access to power supplies e.t.c
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

    9,230
    1,861
    Nov 17, 2011
  10. Sadlercomfort

    Sadlercomfort Ash

    424
    53
    Feb 9, 2013
    Quite straight forward, thanks Harald :rolleyes:
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-