6
\$\begingroup\$

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?

enter image description here

|improve this question|||||
\$\endgroup\$
  • \$\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 '15 at 17:23
  • 1
    \$\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 '15 at 18:07
18
\$\begingroup\$

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

|improve this answer|||||
\$\endgroup\$
  • \$\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 '15 at 18:05
  • 1
    \$\begingroup\$ IEC 60950-1 explicitly proscribes MOVs instead of TVS Diodes, when used as surge suppressors. \$\endgroup\$ – avl_sweden Jul 7 '15 at 15:51
  • 7
    \$\begingroup\$ "Proscribe" means "Forbid". The appropriate word here is "prescribe". Exactly opposite meaning. \$\endgroup\$ – user1713481 Sep 6 '15 at 18:57
  • 1
    \$\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 '17 at 7:54
  • 1
    \$\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 '17 at 7:57
3
\$\begingroup\$

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.

|improve this answer|||||
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.