How to choose a diode for a 3v battery that will be used as a backup power?

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Eugene2021-05-15 17:23:05

Electronics

Eugene, 2021-05-15 17:23:05

I have a device - an intervalometer for the camera. Powered by 3v (two 1.5v AAA batteries). I want to connect this device permanently - replace the batteries with a 3v power supply. Also, in case the electricity is turned off and the power supply unit stops supplying current, it is necessary to provide backup power. As a backup power, you can use a 3V tablet battery. (If the intervalometer is de-energized, then all settings are lost - therefore, backup power is necessary).

I don't have much experience in electrical engineering. The difficulty is to understand how to connect the power supply and the battery in parallel? So that when the power supply is working, the battery does not run out, and when the power supply is de-energized, then use the battery as power. The battery should not receive current from the power supply.

I believe diodes should be used. Which diodes are better to buy? Do you need some special diodes so that the voltage does not sag much?

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5 answer(s)

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Philipp, 2021-05-16
@zoonman

What you are looking for is called an ideal diode . In fact, a diode with a small direct resistance.
You can use the MAX40200AUK+T or the more recent MAX40203 . These ICs are specifically designed to solve your problem. They cost a little more than diodes, but no need to reinvent the wheel.

These microcircuits are on alishka. Not very expensive, but delivery will have to wait.
Good luck!

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milssky, 2021-05-15
@milssky

That's how he did it. Works in a series even.

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Vladimir Kozhevin, 2021-05-15
@vovik0

Instead of diodes, I would put a relay with switching contacts and a coil powered by a power supply - then there will be no losses at the PN junction

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lonelymyp, 2021-05-15
@lonelymyp

The Schottky diode will give about 0.3 voltage drop, you can search the catalogs for the best one and then try to buy it somewhere.
What is the current draw from the battery? You can take germanium D310 and parallel them for more current.

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hint000, 2021-05-16
@hint000

So that when the power supply is working, the battery does not run out

Your circuit is quite possible to use, but a prerequisite: the PSU voltage must be at least a little more than the battery voltage. In this case, D2 will be closed.