Using a TVS diode instead of, or in addition to a MOV for AC line protection?

It comes downto what are you trying to protect against

There are four main types of transient suppression devices

Gas Tube

  • Protection time: > 1us
  • Protection Voltage: 60 - 100V
  • PowerDissipation: Nil
  • Reliable Performance: No
  • Expected Life: Limited
  • Other: Only 50-2500 surges, can short powerlines

MOV

  • Protection time: 10 - 20ns
  • Protection Voltage: > 300V
  • PowerDissipation: Nil
  • Reliable Performance: No
  • Expected Life: Degrades
  • Other: Fusing required. Degrades

Avalanche TVS

  • Protection time: 50ps
  • Protection Voltage: 3-400V
  • PowerDissipation: low
  • Reliable Performance: yes
  • Expected Life: long
  • Other: Low power dissipation. Bidirectional requires dual

Thyristor TVS

  • Protection time: <3ns
  • Protection Voltage: 30-400V
  • PowerDissipation: Nil
  • Reliable Performance: yes
  • Expected Life: long
  • Other: High Capacitance

http://www.onsemi.com/pub_link/Collateral/HBD854-D.PDF

( http://web.archive.org/web/20051001082352/http://www.onsemi.com/pub/Collateral/HBD854-D.PDF )

http://www.vishay.com/docs/88440/failurem.pdf


The overvoltage protection circuit subject is complex and there simply isn't a one size fits all remedy. Things to consider are: where will the circuit be located in relation to the service entrance, are you attempting to protect for short and/or long duration surges, and what type of surge are you planning on protecting against? From my research, the best attempt at a one size fits all overvoltage protection scheme would include line conditioning filtering (inductors/capacitors), (MOV) Metal Oxide Varistors with integral thermal disconnect fuses and Silicon Avalanche Suppressor Diodes. I would talk to the engineers at Littlefuse for advice. They have a large library of downloadable PDF's pertaining to Overvoltage Suppression.

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Tvs

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