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LM2596 expected regulation performance

Stephen Kramer
Prodigy 210 points
Other Parts Discussed in Thread: LM2596, ALLIGATOR

I recently purchased DC-DC buck converters recently with the LM2596 regulator.  I need 0-2 amps out at 5V, with a 12V supply voltage.  I found that the output voltage varies considerably with the load current.  With 12.72V in, I was getting only 3.5V out at 600mA output, with an initial 5V no-load setting.  I attached a chart of measurements.

Is this expected performance for this converter?   If so, is there a converter that has better regulation capability for 0-5V output with 12V input for up to 2 amps output currrent?

Thanks

.

  • 0
    TI__Intellectual 2790 points
    Hi, this phenominoen should be not expected. Could you share us with your schematic and lauout?
  • 0 in reply to Luke Pan
    Prodigy 210 points
    I didn't see on the data sheet how I would calculate the expected voltage drop with varying load. I don't know the schematic, I bough them on Amazon here: www.amazon.com/.../ref=oh_aui_detailpage_o01_s00

    How do you know what the expected voltage drop performance should be?

    Thanks
  • 0 in reply to Stephen Kramer
    TI__Intellectual 2790 points
    Hi,
    Could you probe the Output pin (pin 2) to capture the waveforms? Probe the inductor current if you have a current probe. Also measure the FeedBack pin (pin 4) voltage at 600mA.
  • 0 in reply to Luke Pan
    TI__Mastermind 23815 points
    Hi,

    Could you also tell us at which point do you measure the voltage? Is it at the board or the end of the cable near the load

    Thanks
    -Arief
  • 0
    TI__Expert 4365 points
    Arief and Luke have you on the correct path. You appear to be measuring output voltage downstream from the regulator near your load and the load circuit interconnect has high resistance. (Actually it is (5V - 3.5V) / 0.6A = 2.5 ohms of interconnect resistance between the regulator output and the measurement point.) Instead, measure the output voltage directly at the regulator output using separate measurement leads to the voltage meter. BTW If you are using any bargain basement alligator clip leads on your bench setup, they will often cause this type of measurement error. Even the typical fat Pomona banana leads cause this kind of problem when you draw appreciable current through them, they have a surprising amount of resistance.
  • 0 in reply to Alan Martin
    Prodigy 210 points

    Alan,

    You were right about the wires.  I was using ~18" low-cost alligator clip connecting wires that measured 2.4 ohms each.. When I measured at the converter output the voltage was 5.0V and did not change more than 10 mV up to 600 mA.  I was upset because I have had much anticipation for the new project I am starting, I'm just a hobbyist, I guess I expected failure somehow.

    Several mistakes on my part!  Thanks for your help and insight.  Looking for better wires ...