Current & Voltage Limiter

Discussion in 'The Projects Forum' started by mattd860, Feb 18, 2016.

  1. mattd860

    Thread Starter Member

    Jan 9, 2016
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    Hi All - I'm looking for a fuse (preferably a PTC Resettable Fuse) to limit the max current to 150mA. I'm also looking for a fuse to clamp voltage above 5.5v dc.

    I need this for a fail safe just in case my 5.0v linear regulator ever failed.

    Can anyone refer me to such a device(s) and provide a link to one on Digikey or Mouser?
     
  2. Colin55

    Member

    Aug 27, 2015
    191
    19
    Just use a 250mA fuse and a 5v1 1 watt zener
     
  3. mattd860

    Thread Starter Member

    Jan 9, 2016
    57
    2
    Alright so I understand the 5.1v 1w zener but why use a 250mA fuse instead of a 150mA?
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Google.. 150mA fuse.. plenty to choose from..
     
  5. Colin55

    Member

    Aug 27, 2015
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    What do you think is going to happen if take 150mA??
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Colin, take 150 mA where?

    matt - What response time do you need for your protection? Neither a standard fuse nor a PTC are particularly accurate or fast because they both depend on a small mass heating up for their protection effect. If you are trying to prevent something from being damaged in milliseconds, you will need an electronic circuit rather than a thermal device. Do you really need to shut down the output upon an overcurrent condition, or would a current limiter be sufficient? A current limiter might only reduce the output voltage a bit for a minor overcurrent, or shut it down completely for a current spike.

    ak
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Depending on the time curve... nothing will happen more than likely.. (other that it being a good heater)
    As stated above by AK fuses have time curves (and are slow/horrible for use as a current limit in an application like this)..
    Most if not all can take 100% of the rating for ever without issue and may take 5-10 minutes or more to trip at 125% of the rating,etc... 1 minute at 150%... 1 second at 200%,etc...
    All stated on the specific time curve chart for that fuse..
     
  8. dl324

    Distinguished Member

    Mar 30, 2015
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    Fuses and PTC thermistors probably don't work the way you expect. Have you considered adding current limiting to your power supply? Or a power MOSFET to disconnect the supply if it exceeded a certain voltage?
     
  9. crutschow

    Expert

    Mar 14, 2008
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    Regulators seldom fail.
    What critical circuit are you trying to protect?
     
  10. mattd860

    Thread Starter Member

    Jan 9, 2016
    57
    2
    I'd like to prevent an arduino processor (ATtiny85) and associated circuity from burning out. I have 12v dc in and 5v dc out. If the regulator failed and sent +12v to the 5v circuitry it will likely burn everything up - literally. I don't care if the the processor and circuitry are permanently damaged if the VR fails but I just want to prevent a fire.
     
  11. crutschow

    Expert

    Mar 14, 2008
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    In that case, all you need is a fuse.
     
  12. mattd860

    Thread Starter Member

    Jan 9, 2016
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  13. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Your link doesn't go to a product..
    I'd go for a fast blow 200mA fuse (and fuse holder) to prevent any nuisance tripping..
    And prepare your design for the extra heat (fuses are "heaters")
     
  14. Dodgydave

    Distinguished Member

    Jun 22, 2012
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  15. ScottWang

    Moderator

    Aug 23, 2012
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    What kind of fuse could clamp the voltage?
     
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