Can't get 5v from AMS1117 5v regulator

Discussion in 'Power Electronics' started by zaferaltun, Sep 3, 2016.

  1. zaferaltun

    Thread Starter New Member

    Aug 31, 2016
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    Hello. I'm obeying schematic rules but can't get 5V from the AMS1117 5V regulator with this schematic (see the attachment please). Input and output capacitors are 22uF and here the results:

    R1=1K, R2=3K -> 1.6V~
    R1=47, R2=150 -> 2.55~ and R2 is so hot.

    If I dont use resistors, the output is 5V for a few seconds and then decreased to 1.6V and then the regulator is burning.

    What is wrong with this cheap regulator?
     
    Last edited: Sep 3, 2016
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    How did you calculate R1 and R2.??
    The Vref requires only 50uAmps.
    What is the input voltage and the load resistance.??
    E
     
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  3. zaferaltun

    Thread Starter New Member

    Aug 31, 2016
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  4. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    Check with the datasheet that you have correctly identified the pins on the regulator.
     
  5. zaferaltun

    Thread Starter New Member

    Aug 31, 2016
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    I cant say I wasnt in doubt about the pins. I dont know my regulator brand, bought from China, I checked a lot of datasheet and the pinout shown as in the attachment. The regulator packaging ia SOT223 and I used left pin as GND, center and tab as OUT and right one as IN.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Must be a wrong connection or wrong resistor somewhere. If Vout=2.55V, then even if R1 were shorted the maximum power dissipation in R2 would be 2.55^2/150 = 43mW. R2 would hardly get warm.
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    That would be for the fixed voltage version, according to the datasheet. Yours is the adjustable voltage version!
     
  8. zaferaltun

    Thread Starter New Member

    Aug 31, 2016
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    The pinout is only the alternative I found so far but didnot try. See the attachment please. But if so, how I can get 5V without resistor even for a short time?
     
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  9. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    Note the connections are different depending on whether it is the fixed or variable voltage version of the regulator. You are using the connections for the fixed voltage regulator, but the fixed voltage version doesn't need the resistors. The GND pin should be connected directly to ground.
    What is the marking on the regulator? What characters (if any) follow the ASM1117?
     
  10. zaferaltun

    Thread Starter New Member

    Aug 31, 2016
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    All the text is:
    AMS1117
    5 H517
     
  11. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    Check this list, you seem to have a 5V version.??
     
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  12. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Please clarify. Have you got the fixed 5V output version or the variable output voltage version of the regulator?
     
  13. zaferaltun

    Thread Starter New Member

    Aug 31, 2016
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    I m not sure it is fixed or not. It just writes

    AMS1117
    5.0 H517

    On the chip. I wasnt know pinout could be different between fixed or adjustable since the documentation is single for all types and there is only 1 pinout. Now it seems it is adjustable because it is burning when I connect GND pin to ground directly.
     
  14. zaferaltun

    Thread Starter New Member

    Aug 31, 2016
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    But I really confused. How could I positive voltage if pinout is wrong? The alternative pinout that I attached before is totally opposite of I applied.
     
  15. zaferaltun

    Thread Starter New Member

    Aug 31, 2016
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    I tried alternative pinout without resistor and burned again! Nonsense!!
     
  16. dannyf

    Well-Known Member

    Sep 13, 2015
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    being incorrectly used?

    that's for the adj version.

    you should really read the datasheet.
     
  17. zaferaltun

    Thread Starter New Member

    Aug 31, 2016
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    I read already. Maybe I did not understand or missed some important thing since my english is not so good. I tried lots of combination and I got 3.7V max. I m sure this is absolutely adj version, coz I need absolutely a resistor on gnd pin. Try to read datasheet again! So there is another schema with protection diode,what about it?
     
  18. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    If you are confident that its a adjustable, make R1 a 220R, R2 a 620R and use a 9V dc input, don't forget the 10uF across R2.
    What is the 5v driving into, ie: load resistance.?
    E
     
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  19. dannyf

    Well-Known Member

    Sep 13, 2015
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    Wire it accordingly then.

    Ground the gnd pin, what output voltage do you get?
     
  20. Robin Mitchell

    Well-Known Member

    Oct 25, 2009
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    I would check the authenticity of the chip. I have a Chinese chips 74xx and 4xxx that dont work under feedback configurations that should work with real parts.
    I suspect there is a chance that your regs are faulty.
     
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