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I need to protect the 12.8v regulator from the 14.5v battery.

Do I try to just reduce the battery voltage below 21.8V with a bunch of diodes? Do I just put one diode protecting against current flow into the regulator output? Do I do both? The load operates on 6-36V, and 30w.

The reason I put several diodes in the last option is this. If both the sources are connected I would like the load to take power from the regulator instead of the battery. I thought with multiple diodes in there it would take from the regulator instead of the battery. Am I right?

schematic

simulate this circuit – Schematic created using CircuitLab

The long and the short

Need to protect the regulator from burning. Which option is correct?

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closed as unclear what you're asking by Marcus Müller, Harry Svensson, Dmitry Grigoryev, RoyC, nidhin Nov 8 '18 at 16:44

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ Voting to close as unclear, unless you post a larger image with a proper schematic (@brhans' recommendation is right, use the built-in schematic editor), AND explain what you've considered so far as text in your question (not as a comment). \$\endgroup\$ – Marcus Müller Oct 30 '18 at 17:19
  • \$\begingroup\$ Oh yeah the picture didn't work out right. I will post a schematic. \$\endgroup\$ – thejun Oct 30 '18 at 17:22
  • \$\begingroup\$ Possible duplicate of Voltage sources in parallel? \$\endgroup\$ – Dmitry Grigoryev Oct 31 '18 at 8:40
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Your first 2 options won't work.
Both of them will allow your regulator to be 'back-fed', which is usually not a good thing.
The other 2 will prevent the regulator from being back-fed.
If your load doesn't mind the higher voltage then the extra 3 diodes in option #4 are not all necessary, but you'll probably want to keep one of them unless you intend for your regulator to charge the battery too.

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  • \$\begingroup\$ Thanks for the reply. The reason I put several diodes in the last option is this. If both the sources are connected I would like the load to take power from the regulator instead of the battery. I thought with multiple diodes in there it would take from the regulator instead of the battery. Am I right? \$\endgroup\$ – thejun Oct 30 '18 at 18:08
  • \$\begingroup\$ Yeah - it's less than ideal because you'll waste a little of your battery's energy in the extra diodes, but it will function as you're planning. \$\endgroup\$ – brhans Oct 30 '18 at 19:51

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