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I am doing a solar panel project, but I don't have much knowledge about electronics.

I am planning to use a buck-boost converter that gives me a stable output (12V.)

What happens when the input voltage goes below the recommended voltage (5V?)

Will it cut off or give the wrong output?

REES52 Converter Buck Boost Adjustable Regulator

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  • \$\begingroup\$ Please link to the device data sheet. \$\endgroup\$
    – Andy aka
    Jun 27, 2021 at 9:05
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    \$\begingroup\$ By description it will boost the voltage to the set point when the input voltage is low and buck the voltage when it is high. When the voltage goes below it should shut down it should shut off, but that is part of the individual design. What do the specifications say, your link does not give enough informatio. \$\endgroup\$
    – Gil
    Jun 27, 2021 at 18:45

2 Answers 2

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Most DC-DC chips have an input undervoltage lockout, so if the input voltage drops too low, it's probably going to shut down.

Then, since it is no longer drawing current, the input voltage will rise, and it will turn on again.

So it will cycle between on and off. Whatever you plug at the output may not like that very much.

If the design is too cheap though, and if the manufacturer used MOSFETs that need a bit more gate voltage to fully turn on than the undervoltage threshold of the chip driving them, then it will work with the MOSFETs in linear mode, which will make them overheat and burn.

There's no way to be sure without looking at what the actual devices are.

For a solar panel you should really use a smarter DC-DC like a MPPT. Buck-boost is not that useful, since on a solar panel, when the voltage drops it means there's not enough power (ie, sunlight) available anyway.

At constant output power, boosting the voltage will draw more current from the input, which will make the solar panel voltage drop even more if there isn't enough sunlight. So if you use a buck-boost, you'll have a bit of a "binary" system: either there is enough sunlight to provide the output power you need, and it'll work, or there is not enough sunlight and it will not work at all.

For example you can't use that to charge a battery, because the output charge current setting is constant.

A smarter "MPPT" solar controller will adjust the battery charge current to draw just the right amount of power from the solar panel so its voltage doesn't drop. So it will always give you some power even if the weather is a bit cloudy, your battery will take longer to charge but it will charge. With the buck boost it won't charge at all.

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Will it cut off or give the wrong output.

Probably both, alternately ;)

Seriously though, if you operate a piece of electrical equipment outside its specifications, then you don't know what you're going to get. That's what unspecified means. You have to try it.

If you buy another one, it may or may not do the same thing.

Giving it less than the recommended voltage might even damage it. That's less likely to happen than if you over-volt it, but it's possible. Normally, the input voltage will transition rapidly through the low voltage region. If it stays there long enough to get it to heat up, through drawing high current to try to supply the output power, or something else, then who knows?

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