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What is the simplest and best device (or circuit) to stop the flow of current in a 3.7V (2A) line when current in another 5V (2A) line is present?

Basically I want to make an UPS using a LiPo battery for a SIM800l, I have an SIM800l module attached to A 3.7V wall adapter but I also have connected the SIM800l to a 3.7V LiPo Battery, I want to stop using the battery when there is current from the USB wall charger.

I do not want to use a standard powerbank since these always use the battery.

clabacchio
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S. Feunmajer
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  • An electromagnetic relay. – Andy aka Jul 31 '18 at 16:05
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    That depends on just what your requirements are. Are these two lines feeding the same thing? Or are they isolated? – Hearth Jul 31 '18 at 16:05
  • What is the application? There are chips that could do this. – Billy Kalfus Jul 31 '18 at 16:06
  • Sirius - There's a very simple approach involving diodes, but it can't be used in all cases, depending on the exact circuit. Please edit your question and add details about: (a) what research have you done already, (b) what potential solutions you have eliminated, (c) what you are still considering, (d) what constraints you have e.g. power consumption, size, leakage current when the flow is "stopped" etc.; and (e) add a schematic diagram explaining usage of these two "lines" (I guess they're power rails from voltage sources) to avoid readers giving answers that aren't suitable in your circuit. – SamGibson Jul 31 '18 at 16:19
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    Are you sure this is not another case of XY? Because the mentioned values hint strongly at switching between an adapter/USB and battery. Which is usually done by **voltage**, not current. i.e. the X problem would be: a way to disconnect the output line when voltage on the input line is present. – Maple Jul 31 '18 at 16:29
  • I have updated the question. I mean exactly what user Maple says. Sorry I only have a basic background in electronics – S. Feunmajer Jul 31 '18 at 16:34
  • This really has been asked about a dozen of times. – Marcus Müller Jul 31 '18 at 17:07
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    also: https://electronics.stackexchange.com/questions/165243/usb-power-battery-source-switch?s=1|77.9006 https://electronics.stackexchange.com/questions/226193/switching-from-battery-to-usb-power-source https://electronics.stackexchange.com/questions/96059/switch-between-battery-and-usb-power-no-microcontroller-circuit – Marcus Müller Jul 31 '18 at 17:07
  • I can continue all day long... – Marcus Müller Jul 31 '18 at 17:07
  • What about something like http://www.ti.com/product/TPS2113A or http://www.ti.com/product/TPS2110? – Victor S Jul 31 '18 at 17:15
  • @SiriusFuenmayor - Your update says: "*I have an SIM800l module attached to A 3.7V wall adapter*" I don't think you mean that, do you? I think you mean that you have a __5V__ mains adapter. Please update the question to fix, if my guess about the mistake is correct. – SamGibson Jul 31 '18 at 17:29

1 Answers1

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You can use a basic diode switch like this:

schematic

When 5 V is present, no current will flow from the 3.7 V source.

Whiskeyjack
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    0.6 volts (the drop across the active forward-bias diode) out of 3.7v (or outa 5v) is a significant portion. you might have to accept 15% power loss or, at best, 85% efficiency. – robert bristow-johnson Jul 31 '18 at 21:26
  • @Robert The O.P. wanted teh simplest [sic]. A 15% hit on efficiency is a fair price for simplicity in many cases. – Nick Alexeev Aug 01 '18 at 15:59