Can 5Vdc and Battery Co-exist?

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Old 11-06-19, 07:03 PM
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Can 5Vdc and Battery Co-exist?

I have a project that requires 5Vdc. I have a 5Vdc adapter that I can plug into it or, inside the project, a 3.7Vdc LiPo battery and boost circuit. My question is--can the 5Vdc source and boot source be connected together or do I need to put in a switch that the user switches from 5V to battery or battery to 5V?

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Old 11-06-19, 07:23 PM
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Welcome to the forums.

I would say no. They shouldn't be connected together.
You can use a switch or power jack with an attached switch.
When you plug in the external DC adapter it would disconnect the battery and boost.

Question..... are you planning on leaving the battery and boost circuit running at all times ?
If no..... how will that be switched ?
 
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Old 11-06-19, 07:35 PM
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Thanks Pete! That's sort of what I figured but wasn't sure.

The box will have an on/off switch that turns off the single board computer (SBC), so the battery will be dormant when the SBC is off.

I actually have a small 5V switch module I am thinking of using. When external 5V is supplied, the module will disconnect the battery. Thoughts?
 
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Old 11-06-19, 07:46 PM
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That sounds like it should work.

If your device is not critical that it runs on 5v only....... you could use two Schottky diodes. One in series with the positive of the battery circuit and the other one in series with the positive of the external power supply. A Schottky diode drops .3-.4v. That means you'd end up with 4.6v-4.7v.
 
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Old 11-06-19, 07:54 PM
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Yeah, the SBC is pretty voltage sensitive. In fact, it is rated at 5V but I have a load on it so I have to boost even the 5V source to 5.2V before sending it to the SBC. But...since I have to do that boost anyway, I could boost the 4.6-4.7v to 5.2v. And the LiPo battery output is 3.7v, so it has to be boosted anyway. I'll look into using Schottky diodes. Thanks for the tip!

By the way, based on this scenario, what value of Schottky diode should I use?
 
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Old 11-06-19, 08:47 PM
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The size of the diode is based on the amperage you're going to draw thru it.
A 3 amp diode should be good.
 
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Old 11-06-19, 10:43 PM
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Thanks!! Your advice is greatly appreciated!
 
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