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KIA78R05PI Output 3.45 Volts

Discussion in 'General Electronics Chat' started by Mr_Max, Nov 14, 2017.

  1. Mr_Max

    Mr_Max Member

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    Hi everyone

    I have three 5V LDO regulators labeled KIA78R05PI I have tested the 3 of them with heat sinks Vout is 3.45 volts with no load and as stated in the datasheet
    when control pin is pulled high or open the regulator is on so it's supposed to give 5 volts, am I missing something ? could the 3 of them be wrongly labeled ?!
     

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  2. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    KIA78R33?????

    What is the voltage on the input to the kia78r05?
     
  3. Mr_Max

    Mr_Max Member

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    Vin is 12 volts
     
  4. dave

    Dave New Member

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  5. Colin

    Colin Member

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    Try it on a 12v battery. You must have a load on it. Try 100R
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    It is a low dropout regulator that must have a 47uF capacitor soldered close to its output and ground pins. I hope it is not on a solderless breadboard.
     
    Last edited: Nov 14, 2017
  7. Mr_Max

    Mr_Max Member

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    I have tried a 100uF capacitor still Vout is 3.45 its the value of the capacitor critical ?! yes it's a solderless breadboard, I'll test it after soldering the capacitor.
     
  8. Mr_Max

    Mr_Max Member

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    Still the same Vout 3.45v after soldering a 100uF capacitor to output and ground pins !
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I think KIA is a Korean manufacturer with such poor Engrish that the datasheet is missing the very important maximum allowed effective resistance of the capacitor and its wires (including the poor contacts of your solderless breadboard).

    You do not need a low dropout regulator because your supply voltage is much higher than your output voltage so use an ordinary 7805 that is made in the West so you can see its recommended capacitors on its datasheet.
     
  10. tomizett

    tomizett Active Member

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    If you're just measuring a no-load voltage with a meter 10Mohm then maybe it's just leaking enough to read 3V when "off"? Try placing a small load of 10k or so at the output.
     
  11. Mr_Max

    Mr_Max Member

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    Thanks for the suggestion, I'm making a mini UPS for my router, those 12v feed the router in addition to 5v via L7805 to the charging circuit of batteries, I noticed that while charging the output to the router sometimes drops to 10.8v
    that's why I needed a 5v LDO regulator
     
  12. Mr_Max

    Mr_Max Member

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    Thanks for the suggestion, I have tried that but still the output is 3.45v, although as stated in the data sheet, the regulator is on when control pin is open or pulled high, and close when pulled down, the later is true, when pulled down the output is zero volts
     
  13. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    ?

    You wouldn't need a LDO until at least 6V .. I use a LDO 0n 7v even that's a tad high!
     
  14. Mr_Max

    Mr_Max Member

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    I understand that input to the 5v regulator is 12v, but those 12v feed the router in addition to the charging circuit, which causes the output voltage to drop under load to 10.8v, the router operates on 12v 500ma
    I don't know the exact effect on the router, in terms of increased CRC errors or connection stability during blackouts, which causes sync speed drops, if it has no effect, then I believe it would be fine.
    The mini UPS has 6 cells Li-Ion battery pack, charging circuit, Adjustable step up DC-DC converter , (1N5844 1N5822) O-Ring.
     
  15. tomizett

    tomizett Active Member

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    My mistake - I miss-read the original post.
     

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