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I have an old laptop adapter, with 19 V - 4.74 A DC output ratings. Suppose I need to draw 3 A @ 11.1 V for one of my circuits. I have been doing some research about dc-dc converters and have some questions on my mind.

As far as I understood, I will either buy a dc-dc step down(buck) converter and let it convert 19 V to 11.1 V. Then it will do the job(right?).

However, another option is to buy a more sophisticated one, like this one. (I think giving a link to product will be easier than explain it.)

Now, I read that these buck+boost converters are working with the principle of boosting any input voltage to high DC and then lowering it to the desired(set by user) DC voltage.

My question is, if I plan to draw 3-4 Amps constantly, will this boosting/bucking(?) be too inefficient? I mean, would using a single buck converter be more suitable for such operation? Or there will not be any difference?

Thanks.

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  • \$\begingroup\$ A link to a bona fide PDF data sheet of a product made by a reputable manufacturer and sourced through a reputable dealer is what is required. Bang-good (or bad) or amazon or peebay or aliexpress just don't cut the mustard in my opinion. \$\endgroup\$
    – Andy aka
    May 31, 2020 at 15:35
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    \$\begingroup\$ First, your link is to a buck regulator. Buck only, no boost. Second, the efficiency of most switching regulators increases with output current. That is because as the output power increases, the constant power required to run the regulator circuits at any output become a smaller and smaller percentage of the total power through the device. My vote: a straightforward non-isolated buck regulator rated for 50% more than your max anticipated output current. \$\endgroup\$
    – AnalogKid
    May 31, 2020 at 15:36
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    \$\begingroup\$ Bangood = unreliable. Cheap switching lab supply = unreliable. \$\endgroup\$
    – TimWescott
    May 31, 2020 at 22:00
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    \$\begingroup\$ @muyustan I might first open up the existing 19 V laptop adapter and see if I could modify the existing circuit to achieve my goals. It's not unlikely that there is a method available without all this extra gnashing of teeth over a separate DC-DC converter. Just a thought to consider. \$\endgroup\$
    – jonk
    Jun 1, 2020 at 2:07
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    \$\begingroup\$ @muyustan Hard to say without knowing anything about what I might find when I open it up. I was just saying what I would probably do first, to investigate. Not saying what my crystal ball says I'd find in that hypothetical future. Only you can fix my crystal ball. ;) \$\endgroup\$
    – jonk
    Jun 1, 2020 at 6:44

1 Answer 1

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A simple buck converter should be more than sufficient for your needs. You can try making one yourself with an MC34063 + external switching FET or an LM2596. Modules for both of those are available online as well.

A single buck converter will, in most cases, be more efficient than a buck/boost converter. The latter generally finds applications when you're drawing power from a battery, where the input voltage can vary over a range. Since you're using a laptop adapter, you can expect a steady supply voltage and use a buck converter.

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  • \$\begingroup\$ Ok, thanks for the answer but your mc34063 link says that it is able to handle currents up to 1.5 A only. \$\endgroup\$
    – muyustan
    May 31, 2020 at 15:47
  • \$\begingroup\$ I mentioned that you should use an external FET for switching higher currents. \$\endgroup\$
    – Aniruddha Deb
    May 31, 2020 at 15:57
  • \$\begingroup\$ There are plenty of circuits around for using the MC34063 as a switching controller with external transistors. I wouldn't recommend a switching supply is a first circuit for beginners, though. \$\endgroup\$
    – TimWescott
    May 31, 2020 at 16:33

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