1N5819 diode acting strange???

Discussion in 'General Electronics Chat' started by BillMail, May 26, 2011.

  1. BillMail

    Thread Starter New Member

    May 26, 2011
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    I have a GPS wall charger that isn't charging the GPS even though the charger's power light is on and the GPS light is on when connected. I opened the charger up and tested each circuit component with my multi meter and found that when I put my meter on the diode setting, that one of the diodes (1N5819) seemed to have a reading no matter which side I put the positive and negative leads to.
    Not finding much info on the web on this particular diode, is this normal for this diode?
    I thought all diodes will only have a reading in one direction not both.
    Where can I find this diode...Digikey didn't seem to have it.
     
  2. DigitalReaper

    Member

    Aug 7, 2010
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  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    It depends if there is anything else in the circuit in parallel with that diode.

    Can you test the chargers output directly? Any volts there? (I have the feeling you can't access that point).
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    What do you mean by "it has a reading"?
    Are you using a diode test function on your meter?

    1N5819's are 40v 1A Schottky diodes; they have a low Vf and are fast switching. Diodes do sometimes fail shorted. They can also fail open.
     
  5. BillMail

    Thread Starter New Member

    May 26, 2011
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    ErnieM:
    I am testing at the leads of the diode so there shouldn't be anything else screwing with the results.
    SgtWookie:
    As I stated in my original post ....when I put my meter on the diode setting, that....
    Most diodes that I am aware of will only give a reading in one direction...for example negative meter lead touching the diode lead at the silver band side and positive lead touching the opposite side yields a meter reading of some value. Reverse those meter leads and there is no reading on the meter.

    This diode gives a value (reading) no matter which way I connect the meter leads to the diode, thus my question.
     
  6. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    If the diode is still connected in the circuit it can "give a reading" in either direction. That is not unusual. It depends on the circuit.
     
  7. BillMail

    Thread Starter New Member

    May 26, 2011
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    Thanks for that bit of info. I will disconnect one of the diode leads from the circuit board and try again. I assume doing that should yield a reading in one direction only for this diode correct?
     
  8. tom66

    Senior Member

    May 9, 2009
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    How is the diode connected to the board? It is possible it is an input protection diode, to prevent damage from reversed polarity. But it could also be used in a switchmode PSU. In which case you could be measuring the inductor, or the internal power switch of some IC.
     
  9. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
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    That should be enough to isolate the diode from the rest of the circuit.
     
  10. BillMail

    Thread Starter New Member

    May 26, 2011
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    Isolated the diode and it is functioning properly. That was my last hope for trying to figure out why my GPS charger shows power on the charger and GPS and yet doesn't charge the GPS battery.
    Oh well, off to get a new charger.
    Thanks to all for the help
     
  11. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Are you sure the battery is good?
     
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