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In my project, I have an input of 3 volts to 12 volts DC, but I need a minimum 5 volts DC. If I use a 7805, it will not work under 7 volts. If I use a boost converter or buck converter, I can't control them as in case of boost converter ViVo. What should I use to get constant 5 volt DC output?

JRE
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Debdeep Ghosh
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  • You may want to look at "step-up step-down converter". Given a input range it can regulate to the desired voltage. – Mat Mar 17 '22 at 12:03
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    Does this answer your question? [How can I get a stable 12V output from a motorcycle battery?](https://electronics.stackexchange.com/questions/610782/how-can-i-get-a-stable-12v-output-from-a-motorcycle-battery) - the voltages are different but the solution is the same. – Andy aka Mar 17 '22 at 12:41

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You need a so-called "Buck-Boost" converter. This will do it! I had the same "problem", I use one using the LM2587.

See my post: MCU 'remote control' of DC-DC converter's Vout adjustment potentiometer

Nice greetings!

bernd2700
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    The LM2587 is a boost converter, not buck-boost. It won’t do what OP wants, not even when wired as a flyback. – hacktastical Mar 17 '22 at 17:17
  • Sorry, I have the thing at home and MEASURED (!) it in a complete small PCB in a Buck-Boost configuration. If I write "I already USE it", you cannot say, "it is not possible with this chip", if the unit is lying around in my cellar and in operation! Please do not confuse the audience here. Sorry to have to state this clearly again (that the LM2587 CAN be used as a buck-boost - I mean what shall I write more than "I USE it") No offense – bernd2700 Mar 17 '22 at 20:30
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    @bernd2700 Wouldn't it make more sense to recommend a part designed for this role (buck-boost topology) - there are _tons_ of options - rather than a flyback switcher _used outside its specifications_? The latter is never good engineering practice. And, sorry, personal testimony is the weakest form of scientific evidence. But I'm glad you have a solution you are personally happy with. -1 – TypeIA Mar 18 '22 at 05:11
  • Hi TypeIA, Sorry, you are right, it's really outside its spec, because he has written 3 V, I oversaw that! I have 4 V as min. & it works fine. But: It's NOT a flyback, it's a buck-boost! (Literature: "A flyback converter is isolated by a coupled inductor while a buck boost converter has a common ground with input and output.") => And I DO HAVE common ground! So it IS buck-boost topology! I have not understood what you mean by "personal testimony is the weakest form of scientific evidence". I have googled it, but found no translation. I hope good enough evidence when I say, I "MEASURED" it. – bernd2700 Mar 18 '22 at 07:34
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    @bernd2700 Thanks for the clarification. To explain the "personal testimony" sentence: it means someone saying "I know X is true, trust me" isn't convincing. Most of us know at least one person who claims ridiculous things like having been kidnapped by aliens. I'm not saying you're such a person, but a random person on the Internet (again, no offense intended) saying that something works is not a good thing to build an engineering decision on, whereas published capabilities in datasheets from a reliable manufacturer is. – TypeIA Mar 18 '22 at 09:22
  • Hi TypeIA, ok, thanks, understood. Do you want me to do a video? E.g. I set the input voltage to 6 V and turn the output from 4V to 14V (this case I have prepaired with the potentiometer and resistors). And where I measure "live" the 0 Ohm ground connection of the input & output? But where to post it? Only a photo could have more fake character - in the sense I just copied it from anywhere. If I make a video instead, where you see my fingers turning the pot. and see the display of the DMM, I think it is more authentic. I do not know how to more "evidence" it, if not by a real measurement! ;-) – bernd2700 Mar 18 '22 at 10:27
  • It has a minimum Vin of 4V. Even wired as a flyback it will not work. – hacktastical Mar 18 '22 at 05:02