I have a simple question, I am a beginner in electronics and I need advice and help from a professional.

I have a battery with a maximum voltage of 30 volt. This is my power supply for my projects (Arduino + relay + SIM800L.)

I need a constant fixed output voltage and current (5 volt and 2 ampere) for input voltage 10-30V. My battery voltage slowly decreases from 30V to 0V, but I need to work my device from 30V to 10V with fixed output.

Can I use an LM2596S buck converter DC-DC 4.0-40V to 1.25-37V 2A voltage adjustable regulator?

  • 1
    \$\begingroup\$ You can't fix both voltage and current at the same time. Pick one. \$\endgroup\$
    – brhans
    Apr 10, 2022 at 16:41
  • 1
    \$\begingroup\$ This is a common error -- if you're driving a two-terminal device, you can control either voltage or current. Not both -- physics doesn't allow that. Many voltage regulator circuits will hold a voltage until the current hits some maximum, then control the current (or the relationship between relationship). But not both at the same time. Please edit your question to describe what you're really doing, and why you think you need to control both. \$\endgroup\$
    – TimWescott
    Apr 10, 2022 at 16:48
  • \$\begingroup\$ What sort of battery are you using (Lead-acid, Lithium, ...)? Discharging a 30 volt battery below 24 volts or so will serieously damage the battery. \$\endgroup\$ Apr 10, 2022 at 17:33

1 Answer 1


You may have red 2A is printed in the specs of the communication board. It means the max current draw of the board if the nearest cellphone link is distant and the board uses its max transmit power to stay connected. The 2A mentioned in your power supply option specs is the maximum allowed total current draw done by all simultaneously running loads together.

Seems that the power supply board at least is promised to be able to feed your communication board ( I do not know does it really work as promised). But it cannot feed anything else at the same time. BTW the communication board expects 4.1V, 5V is too much.

Nobody knows how much the power supply board radiates disturbing noise signals to the environment. That noise may prevent the wanted radio communication. Suppressing radio noise emissions is your duty because you use a component, not a ready to use consumer appliance. Battery has not that problem.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.