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I am creating powering board for LED strips inside the cacti glass house. It consume 12V DC around 2 amps. I would like to power them up from battery (charged by solar, lead-acid battery 20Ah), but if there is no energy left, switch to DC power supply (12vdc).

I found the answers that it is possibly made by diodes here. But I do not fully understand, I am a programmer with no electro background, so I am a beginner (and I love it :)). I do not understand how to wire the diodes to do the job.

I understand that it will choose higher voltage, so when the battery drops down below some limit, it will take power from the power source. But how to do it, please?

Mlok
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    Possible duplicate of [How can I seamlessly switch power supplies?](https://electronics.stackexchange.com/questions/121496/how-can-i-seamlessly-switch-power-supplies) – Marcus Müller Jun 29 '19 at 10:56
  • I have read to that question, but I would prefer diode solution, but don't know how to wire it – Mlok Jun 29 '19 at 11:19
  • It's just two diodes! Try googling and look through the images, so easy. If you can't do that, you shouldn't be doing this. – Jodes Jul 12 '19 at 09:53
  • Possible duplicate of [OR-ing power supplies (diode or mosfet)](https://electronics.stackexchange.com/questions/96398/or-ing-power-supplies-diode-or-mosfet) – Jodes Jul 12 '19 at 09:54

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schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Diode connection.

There will be a small voltage drop (0.7 to 1.0 V) across the diodes but it shouldn't cause any problems.

Transistor
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  • Thanks so much, it looks simple I will try this. As I think it uses higher voltage source to power up the load? Should I give the diode on Vcc and GND or just on Vcc please? – Mlok Jun 29 '19 at 12:14
  • Yes, the higher voltage will win. The other diode will be reverse biased and so will not conduct. See my article [LED -> diode -> non-return valve](http://lednique.com/what-is-an-led/) for some explanation. Diodes are only required on Vcc. – Transistor Jun 29 '19 at 12:17
  • Oh great thanks so much. I will try it as soon as the temperature will drop in the evening (37 deg celsius now). Thanks for great article! – Mlok Jun 29 '19 at 12:19
  • Thanks so much for the help! – Mlok Jun 29 '19 at 17:42