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I have been trying to source a Buck/Boost IC to design a circuit for my needs but I'm having a little trouble understanding how I would do this.

I am currently designing a circuit that will provide a regulated 12V output (around 3A max) from either a 12V battery or 12V DC input.

My go-to would be an adjustable linear voltage regulator, but these can only step down to voltage levels that are less than the voltage input (dependant on the dropout voltage of the regulator). As battery voltages will decrease over time (approx 12.65V to 11.9V) the linear regulator would not suffice (Not to mention that 12.65V is within the voltage dropout range of the linear voltage regulator when it is set to output 12V).

I could decrease/increase the input voltage and combine that with a boost or buck/linear regulator to achieve a 12V output but I would prefer to keep the input as 12V.

I found this post (Stabilize 12V to 12V) which recommends a Buck-Boost Converter. This seems like it would work for my application.

I've had a look on RS components through some datasheets but the typical circuit applications either show the IC in Buck or Boost configuration and not as a Buck-Boost. (Example TI MC33063AP)

Therefore, I was just wondering if there were some pointers on how to construct a suitable circuit for this application. For example, some ICs seem to mention PWM control, I assume this would mean I need to include something like a 555 IC to control the buck/boost functionality?

There also seems to be a lot of terminology for Buck-boost (Buck boost switching regulators, Buck boost controllers, Synchronous buck boost etc..) is there a particular type that would be best suited to this application?

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  • \$\begingroup\$ Can you convince me why you would need to design this thing "from scratch" while there are perfectly usable, cheap, ready to go, modules out there like: ebay.com/itm/… I'm an EE and could design such a thing myself yet I would just buy that module instead and save time and money. Also: you mentioning a 555 in this context means you have a lot to learn before you can even design this thing yourself. \$\endgroup\$
    – Bimpelrekkie
    Commented Apr 28, 2020 at 10:57

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I could decrease/increase the input voltage and combine that with a boost or buck/linear regulator to achieve a 12V output but I would prefer to keep the input as 12V.

Well, that's what a buck-boost regulator does so, when you say this in the next paragraph...

I found this post (Stabilize 12V to 12V) which recommends a Buck-Boost Converter. This seems like it would work for my application.

You are inadvertently forming a contradiction (no problem, just saying).

I've had a look on RS components through some datasheets but the typical circuit applications either show the IC in Buck or Boost configuration and not as a Buck-Boost.

Well, they do have a section called buck boost: -

enter image description here

Try this link to the above page and note that top of the list is the MC34063 (similar part number to what you referred to) and might be very similar but make by ON semiconductor rather than TI but, do read the data sheets carefully.

For example, some ICs seem to mention PWM control, I assume this would mean I need to include something like a 555 IC to control the buck/boost functionality?

No, that won't be needed - buck-boost chips will have this built inside for controlling the transistors associated with the circuitry.

is there a particular type that would be best suited to this application?

Generally I don't use RS or FEC to search for what I want, I got direct to TI or AD and use there search engines. For example this one by AD (Analog Devices): -

enter image description here

Press "search" and it comes up with 13 options: -

enter image description here

I browsed down that list and half-heartedly chose the device that appeared to use the fewest components: -

enter image description here

But I could have gone to choose a device that used internal transistors (if there were one that would do 3 amps) and find just one suitable device: -

enter image description here

If you need any more help choosing just say.

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  • \$\begingroup\$ The LTC3119 looks perfect, however I can't seem to find a through hole equivalent of this. I'll have a look. Thank you for your detailed response! Just to confirm, I found the page you found on RS, I was looking at the MC34063 IC, however the descriptions seem a little ambiguous. It lists the IC configurations for step up/ step down for specific voltage inputs. However they don't explicitly say the IC can be used in buck-boost (non-inv), e.g Vout=x and x-2<Vin>x+2. Is there a subtle difference, or is it the same thing? Sorry for the stupid questions, this area is quite new to me. \$\endgroup\$
    – dyode254
    Commented Apr 28, 2020 at 14:36
  • \$\begingroup\$ @dyode254 good spot - the MC34063 can be used as either one or the other but not both simultaneously. This is one of the problems of vendor lists. You'll be lucky to find a proper buck-boost in non surface mount. Have you thought about buying a ready made module? Of course you could use too devices (one buck and one boost) but that kind of seems to miss the point. \$\endgroup\$
    – Andy aka
    Commented Apr 28, 2020 at 14:45
  • \$\begingroup\$ Thank you for clarifying, I'm currently looking at the LT1172CN8#PBF which lists a "Negative-to-Positive Buck-Boost Converter" not sure if this could be suitably modified? I have, I'm currently designing a PCB, I'd just rather it was all on one board rather than having to make a box that requires mounting for various boards. I did also think that. surface mount wouldn't be the end of the world. It just makes it harder to remove components my end should I want to upgrade/repair parts. \$\endgroup\$
    – dyode254
    Commented Apr 28, 2020 at 15:18
  • \$\begingroup\$ No I don't think it can. You might consider a flyback converter - getting them in pinned devices might be possible. \$\endgroup\$
    – Andy aka
    Commented Apr 28, 2020 at 16:36
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well use a LM338 regulator to make 12V from an input supply of say a battery which operates from 11.8 volts to say 14.4 volts - cycling with an intelligent battery charger.. then build the MC34063 boost circuit .. which is very simple and very smart.. it will work well within the input voltage range offered by your LM338 circuit.. QED..!!!

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    \$\begingroup\$ This answer would become more useful if you include a schematic and preferably some simulation results. \$\endgroup\$
    – Syed
    Commented Nov 24, 2021 at 5:00

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