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A few months ago I used a L298N module (actually the Velleman VMA409) and I managed to make my motors working fine.

However now that I want to reuse it for another project something seems off: The regulated 5V output is always equal to the 16V VMS input.

To give more details:

  • I'm powering the board with 4x 3.7V 18650 batteries in series for an input of about 16V. This should be OK since according to the specs the range for VMS is 5V-35V
  • I'm reading the output value on the two pins I marked with an arrow in the following picture (using both of the GND pins) and in all cases I get about the same value as what I have on VMS.
  • This is when I have the 5V_EN jumper in place, if I remove it I get no output at all (Which I think is normal, since that disable the internal regulator)
  • For now I haven't connected my arduino because I want to understand what's going on before, so the Inx and EnX pins are connected to nothing.

So my questions are:

  • Is it indicating that I somehow fried my driver board?
  • Can I get back this 5V regulated output?

enter image description here

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  • Does the LED go on with only VMS connected and the 5V_EN jumper in place? – ocrdu Nov 13 '20 at 15:50
  • your question is not about an arduino, so it is off topic here – jsotola Nov 13 '20 at 15:50
  • It's more of an EE question, yes. If you ask it there, here is a link to the schematic: velleman.eu/downloads/29/infosheets/vma409-schematic.pdf – ocrdu Nov 13 '20 at 15:59
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    Sounds like the regulator has "failed short" – Majenko Nov 13 '20 at 16:25
  • @ocrdu The LEDs do go on with only VMS connected and the jumper in place. But I'm not sure what that would mean? @ Majenko: What would be the consequences of the failing regulator: Is it still safe to use the module if I don't rely on the 5V output? Also how can I have fried this regulator? – statox Nov 14 '20 at 19:01
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You are making an incorrect assumption, the L298N is an "H" bridge driver for small motors, not a 5V power supply. The 5 volt output is provided by a separate 78L05 regulator on the module. This regulator cannot supply much power. Take a look at the schematic link given to you by ocrdu. Be sure all the grounds are connected.

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