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    UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 volt...

    I got a problem, i need 3,3 volt for a mems microphone test, so got some small SMD version (SOT223) UA78M33CDCY voltage regulators.
    They are connected the standard way, 0,1 nF to ground on output, and 0,33 nF on DC input to ground, and i also had a 560 ohm resistor on output to ground to ensure some current draw.

    Here is the problem, it regulates fine to 3,3 volt at input supply voltage betveen 5 to 11 volt, but above 12 volt in, it suddenly raise output voltage dramatically, 5, 6,7 volt, and then often burn off, sending input voltage directly to output.......
    At 14 volt....the output has raised from 3,6 volt, into 7 volt.....
    As i can read from datasheet, these regulators shoul be able to take Vin from 5 to 25 volt........so why are mine crashing above only 12 volt?
    I have tried ti raise the out cap into 10 uF....that did not help either.....what can be wrong?

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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    the data sheet for the 3.3 V part is up to 20 V input, not 25V
    but that's splitting hairs compared to your reported results

    is there a load in addition to the 560 ohm resistor?
    did you lay out the PWB per the data sheet and the appropriate case?
    if not, it may be getting too hot, as the PWB copper layout is much larger than the pins, especially the common
    the thermal resistances are specified assuming a specify heat sink or PWB layout

    if the goal is the test the microphone, and you can get 3.3V reliably at 9 or 10 V input,
    is it necessary to raise the input voltage above 10 or 11 V?

    the operation of this regulator is a separate issue



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    Hi,

    I only have the 560 ohm load since i thought that maybe the regulator need e little current draw, around 5 mA, to work correctly, an it does not even gets warm.
    Right now when i test i, i do not have it on a pcb, just soldered together on the table.

    I can live with the 11 volt in the mems micriphone setup, i am just pusseled with why this is happening.



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    its not clear, since its supposed to have over current and over temperature protection built in



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    Where did you buy them?
    They may be counterfeit parts.
    Zapper
    Curmudgeon Elektroniker



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    Hi,

    You say:
    They are connected the standard way, 0,1 nF to ground on output, and 0,33 nF
    But the datasheet says 100nF and 330nF, not 0.1nF...

    Show your complete test schematic and correct values.
    A photo of your circuit could also give useful information.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    Sorry, i meant 0,1 uF and 0,33 uF, thats the values i use.

    I bought them on Aliexpress.......



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    just for fun, try one or two from digikey, or newark, or jameco,
    all of whom have been around for a long time.

    or, maybe direct (?) from TI

    or, get a larger case, such as TO220



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    Just ordered some samples directly from TI......so lets see.....



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    Quote Originally Posted by Mtolesen View Post
    Just ordered some samples directly from TI......so lets see.....
    Good. AliExpress sells cheap Chinese junk.


    1 members found this post helpful.

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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    There is always this ordinary voltage regulator made from an NPN and zener diode.

    The zener can be a string of led's and/or diodes. It can even include a low-ohm resistor although regulation is not as tight.

    Click image for larger version. 

Name:	series voltage regulator NPN 4v zener load gets 3_3v from supply 4-12v.png 
Views:	1 
Size:	21.0 KB 
ID:	153761



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    Quote Originally Posted by BradtheRad View Post
    There is always this ordinary voltage regulator made from an NPN and zener diode.

    The zener can be a string of led's and/or diodes. It can even include a low-ohm resistor although regulation is not as tight.
    And it has has no overcurrent or overtemperature protection.
    Zapper
    Curmudgeon Elektroniker



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    Problem solved!
    I ordered excately the same ua78M33CDCY from Texas instruments......and they work perfect!......they regulate to 3,3 volt allthe way from 4 volt to 25 volt!

    So.....Aliexpress sold me bad ua78M33CDCY`s.......a secondhand batch that didn`t really work.



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    Bad or counterfeit semiconductor parts from China is very common.
    They seem to have no control over (or interest in controlling) the sale of such parts.
    Generally it's not worth taking the chance to buy semiconductors from Chinese suppliers just to save a little money.
    Zapper
    Curmudgeon Elektroniker



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    Hi crutschow,

    Yes, i see, i was wondering where/how they get these bad semiconductors, i mean, semicondunceter manufactures are no a backyard shop....it is big plants, with quality control, and i wouldthing that bad chips were destroyed already in production test even before they were placed in the chip housing.



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    Re: UA78M33CDCY 3,3 volt regulator will not regulate at input voltage above 12 vol

    They are not necessarily rejects from a reputable manufacturer.
    Semiconductor plants in China actually produce counterfeit parts on purpose, obviously with little quality control, since their name isn't on the device.
    I've also heard of the removing the part numbers and substituting the number of more expensive type parts.
    Zapper
    Curmudgeon Elektroniker



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