Connect with us

Fake LM2596?

Discussion in 'General Electronics Discussion' started by holex, Nov 5, 2014.

Scroll to continue with content
  1. holex

    holex

    21
    0
    Jun 2, 2014
    I have bought an LM2596 on Ebay. I have checked its output by an oscilloscope, but its frequency is only 55 kHz, not 150. Have I bought a fake item?
     

    Attached Files:

  2. davenn

    davenn Moderator

    13,793
    1,938
    Sep 5, 2009
    hi there
    welcome :)

    ummm first question .... was it regulating your voltage correctly ?

    The 150 kHz osc is all internal, chances are you are not going to be able to measure it any way
     
  3. holex

    holex

    21
    0
    Jun 2, 2014
    Hi!
    Yes, voltage is correct, but I have to use other inductor and capacitor value if frequency is lower.

    I should be able to measure a 150 kHz square wave on the output if load is high enough. Or I'm wrong?
     
  4. holex

    holex

    21
    0
    Jun 2, 2014
    This picture is from the datasheet. Here the period time is 7us (-> frequency is 143 kHz).
    If you see my oscilloscope screeshot, the period time is 18us.
     

    Attached Files:

    • ds.png
      ds.png
      File size:
      169.1 KB
      Views:
      218
  5. davenn

    davenn Moderator

    13,793
    1,938
    Sep 5, 2009
    I would be surprised if you can ... the osc signal doesn't appear directly at the output

    LM2596.GIF
     
  6. holex

    holex

    21
    0
    Jun 2, 2014
    Okay, thank you. But why is the frequency 143 kHz in the picture from the datasheet?
     
  7. davenn

    davenn Moderator

    13,793
    1,938
    Sep 5, 2009

    I don't know which pic you are referring to ??
     
  8. holex

    holex

    21
    0
    Jun 2, 2014
    See the #4 answer.
    Or check the datasheet on page 8.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,482
    2,830
    Jan 21, 2010
    Check to see if the frequency increases with load. The regulator may be operating in burst, or stop-start, or non-continuous mode if it has a relatively low load on it. What this means is that a single "on" cycle raises the voltage above the set point and it takes more than the remainder of the cycle for it to drop below the set point again, so the regulator skips cycles to prevent the voltage from rising too high.

    It's still possible that you have a clone chip, but it may not necessarily be a fake.
     
    BobK and KrisBlueNZ like this.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-