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I want to power 5v leds from a 12v source in my car using a "DC-DC Adjustable Step-down Buck Converter LM2596 3A". The source has a dimmer switch which can regulate the voltage from 12v to 1.25v reducing brightness of the instrument cluster.

What will happen if the input voltage falls below 5v? For example 2.5v, does the output voltage also drop to 2.5 and thereby reduce the brightness of the 5v leds? Or will the step down converter not allow current to flow at all?

Thanks in advance :)

The step down converter: https://www.tinytronics.nl/shop/en/power/voltage-converters/buck-(step-down)-converters/dc-dc-ajustable-step-down-buck-converter-lm2596-3a

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  • \$\begingroup\$ refer to the device datasheet for information about undervoltage behavior \$\endgroup\$
    – jsotola
    Mar 13, 2022 at 23:41
  • \$\begingroup\$ Hmm, I am experiencing some very odd behavior using the DC-DC buck converter. When the buck converter is connected to adjustable dimmer 12v input source in the car, and I try to lower the input voltage, the input does not go below 8.6v. However, if the buck converter is not connected, the dimmer can to down to 1.16v - I can literally see that when connecting the converter, the brightness of the lights that are regulated by the dimmer is increased. The buck converter is set to 5v output. How can it affect the input voltage? \$\endgroup\$
    – siz
    Mar 19, 2022 at 18:07
  • \$\begingroup\$ As a side note, why do you expect your 12 V in the car to go as low as 2.5 V? If that is battery derived - and what isn't? - surely it won't reach those voltages, and if it does, the LM shutting down is the last of your problems. \$\endgroup\$
    – Vladimir Cravero
    Mar 22, 2022 at 15:52
  • \$\begingroup\$ @VladimirCravero I do not expect the battery voltage to go down to 2.5v. The BMW F3x's have 12v (via 20 amp fuse, if I am reading the fusebox diagram correctly) going to the instrument cluster and ambient lighting through a dimmer/potentiometer(?) which controls brightness of the cluster/lighting. The voltage reading when at lowest setting is 1.2v and at highest is 12v. \$\endgroup\$
    – siz
    Mar 22, 2022 at 16:38
  • \$\begingroup\$ Understood. I don't fully know the limitations you are working with, but in case you want some lights to be on when cockpit lights are on, but not to be dimmed, it should be possible to use the 1.2 .. 12 V signal to trigger a relay that powers your DCDC off the battery directly. If this is the case, ask a new question about this and we can surely help you. \$\endgroup\$
    – Vladimir Cravero
    Mar 23, 2022 at 11:03

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LM2596 shuts down when input voltage below 3v, so I have to find another solution.

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