SMD diode

Discussion in 'General Electronics Chat' started by Dritech, Sep 17, 2014.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi all,

    Can an SMD reverse polarity protection diode be damaged by ESD? If yes, can this parameter be found on the diode datasheet?
     
  2. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Also, apart from peak inverse voltage and maximum forward current, what can cause a faulty diode?
     
  3. Vojtrex

    New Member

    Sep 17, 2014
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    It varies from piece to piece. As far as I know LEDs are more vulnerable to ESD than some integrated circuits/microchips.

    Look for preferences of InGaN light-emmiting layer (common in LEDs)

    Some LEDs incule a Zenner diode as well, in case of ESD "destruction".

    hope this helps
     
  4. Vojtrex

    New Member

    Sep 17, 2014
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    sorry, I thought you were talking about LEDs. ¯\_(ツ)_/¯
     
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
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    It is a routine procedure to reverse breakdown diodes to measure what the breakdown is. As long as the current is controlled there is no damage.
     
  6. alfacliff

    Well-Known Member

    Dec 13, 2013
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    back in the oldeer days of cb repair, a lot of radios came in with shorted reverse protect diodes, someone would hook the radio up backwards, blow the 2 amp fuse, and replace it with a 20 amp fuse, this caused the diode to short. never found an open one, only shorted.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
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    Reverse polarity protection to what?!

    There are various configurations for input protection diodes - in extreme cases they can fail during the duty of protecting the main circuit.

    There are 2 main configurations of supply reversal protection diode - the shunt variety *SHOULD* have a fuse that blows if the battery gets reversed and forward biases the shunt diode.

    The other type uses a series diode that only conducts when the battery is right way round, the reverse voltage rating should be easy to track down from the type number. Sometimes the forward volt drop of a regular silicon diode takes too much of the available voltage, so a Shottky barrier diode is used for its lower Vf, you have to be a bit careful with SB diodes - they start from only 20V reverse rating, and aren't common above 60V. With such low breakdown rating, the risk of static damage is something you should take seriously.
     
  8. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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  9. ian field

    Distinguished Member

    Oct 27, 2012
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    ESD is (hopefully) low energy and can't cause enough heating effect to melt bits off of switch contacts, but its more than enough to punch through the delicate gate layer in MOS devices.

    The back emf from inductive loads like relays is another matter, without a clamp circuit you can get a fat spark every time the switch breaks the current.

    Capacitive loads are different again, the charging/discharging surge can in extremes weld switch contacts together - which takes us full circle to ESD, if the charged object is big enough to have significant capacitance to ground, it can deliver an impressive spark big enough to damage more than just sensitive semiconductors.
     
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