Negative voltage from LM2596 DC-DC Ebay module

lm2596
Some months ago I bought on Ebay 5x DC-DC adjustable switching converter  module for few euros.
As suggested in the datasheet, an additional LC output filter must be used to reach an acceptable voltage ripple.
For an ongoing project I need a source of negative voltage of12V @ 100mA, so I looked for a way to modify one of these modules.
The solution is very simple and it is not necessary to unsolder any component, it is sufficient to use the points of the input and output voltage as specified in the picture below
bottom
To obtain a negative voltage, the input/output GND must be connected to the left two pins of the trimmer (OUT+ signal on the PCB silkscreen)
Below the pictures of the -12v output with no load and with a current of 150mA:

The ripple is about 120mV, it can be reduced with a filter on the output, I used an inductor series of 1uH and a 220uF capacitor to GND:

The ripple is now reduced by 5 times, around 25mV also with a drain of 500mA.

NOTE: In the inverting regulator mode, the LM2596 needs at least 2A input for a correct bootstrap, see the datasheet for a delayed-startup trick, if you doesn’t have that current.

NOTE2: of course, if wired in inverting mode, the module should be installed isolated from the GND

Hope this helps someone looking an easy and cheap source of negative voltage with good current.

 

8 Responses to “Negative voltage from LM2596 DC-DC Ebay module”

  1. Hi there,

    I’m trying this method but when I enable output on the DC power supply, I see that the input voltage drops to 1.3V and the current rises to 660mA, where the supply gives an error the red dot, that the circuit drives too much current. I have +12V on In+, nothing on In-, nothing on Out+, the pot is soldered like in the piture and I have a probe attached to the Out-. Any ideas?

    Thanks in advance.

    • Maybe your power supply cannot handle the peak of current during the “bootstrap” of the converter. Try with a bigger ps or a battery. Make sure your module’s pcb is floating.

  2. Please, I need to supply +12V and -12V to a circuit. Do you think it’s possible to use two modules for that? When I read your article, I had hope it was possible, but when I read your note 2 ( of course, if wired in inverting mode, the module should be installed isolated from the GND), I understand it’s not possible to join both modules grounds. What should I do to have -12V and +12V using two modules and a common ground? Thanks!

  3. Yes you can use two of them, positive and negative with same GND. What I meant to say is that the negative voltage generator cannot be installed in the usual way with the screws in their pcb’s holes connected to ground, keep it floating. Use nylon pcb spacers or similar.

  4. I have done more modifications to the board but this does not have isolated ground:
    http://m0dts.co.uk/?tag=Mods&item=102

    • Seems a bit more complicated than solder 3 wires, but in some situations a floating pcb can be a problem. Good job and thanks for sharing!

  5. Wanted to say thanks for posting this! You’ve answered the question perfectly and enabled me to move forward on a few audio projects without needing to buy negative PSU’s– instead using the half-dozen of these DC/DC converters I got laying around. Thanks again!
    By the way, giving the converter a standard input 12V+ and GND yet flipping the polarity of the output, on a voltmeter, I show a “neg” voltage. Can you tell me why the extra bridging of the ver. resistor is needed and/or why simply flipping the output polarity would not work?? Thanks!

    • In this module the input GND and OUT- are connected, so you can’t connect the OUT+ to GND and use the OUT- as a negative voltage. Other DC-DC converters have input and output fully isolated and you can fix to the common GND the OUT+ or OUT- if needed.

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