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For 220 V AC mains voltage, is it good practice to replace a 300 V MOV with a 300 V bidirectional TVS diode (like in here http://www.littelfuse.com/products/tvs-diodes.aspx), or connect both in parallel? Are there any points that need to be considered?

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    \$\begingroup\$ A MOV is a TVS. If you're talking about putting a Zener type TVS in parallel with a MOV, there isn't much to be gained there. \$\endgroup\$
    – Matt Young
    Feb 1, 2015 at 17:23
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    \$\begingroup\$ Can you explain why? Can't I benefit from the faster response time of the TVS diode? Keep in mind I'm asking both about replacement and connection in parallel. \$\endgroup\$
    – downthewire
    Feb 1, 2015 at 18:07

2 Answers 2

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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

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  • \$\begingroup\$ Sorry, I should have been more clear, I'm talking about TVS diodes like in here : littelfuse.com/products/tvs-diodes.aspx. \$\endgroup\$
    – downthewire
    Feb 1, 2015 at 18:05
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    \$\begingroup\$ IEC 60950-1 explicitly proscribes MOVs instead of TVS Diodes, when used as surge suppressors. \$\endgroup\$
    – avl_sweden
    Jul 7, 2015 at 15:51
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    \$\begingroup\$ "Proscribe" means "Forbid". The appropriate word here is "prescribe". Exactly opposite meaning. \$\endgroup\$
    – user1713481
    Sep 6, 2015 at 18:57
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    \$\begingroup\$ "1.5.9.1 General It is permitted to use any type of surge suppressor, including a voltage dependent resistor in a SECONDARY CIRCUIT. If a surge suppressor is used in a PRIMARY CIRCUIT , it shall be a (VDR), and it shall comply with Annex Q." \$\endgroup\$
    – avl_sweden
    Apr 3, 2017 at 7:54
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    \$\begingroup\$ The standard then goes on to state: "NOTE 1 A VDR is sometimes referred to as a varistor or a metal oxide varistor (MOV). Devices such as gas discharge tubes, carbon blocks and semiconductor devices with non-linear voltage/current characteristics are not considered as VDRs in this standard." \$\endgroup\$
    – avl_sweden
    Apr 3, 2017 at 7:57
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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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