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I just read about buck converters and boost converters and buck/boost converters. Great stuff.

But, why is a step-down converter called a buck converter?

I tried to research this myself. According to Google Book search, the phrase buck-boost transformer was in use at least as early at 1891 in a periodical called Architectural Review.

Adam Haun
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daveloyall
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    I suspect the term as applied in electric systems may have been created originally for transformers -- more specifically for autotransformers -- and relates to an idea that was commonly known back in the day. Logs were bucked (either under- or over- bucked) depending on from which end of the log sections were cut for milling. (Starting at the thicker base and working up or starting at the top and working down.) A bucking transformer can be seen as doing just that. And I suspect that's where the first author of the term got the idea since logging was a commonly shared experience in the 1800s. – jonk Aug 29 '19 at 00:14
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    I don't think it's opinion-based. Personally I don't like etymology questions, but if we don't want them anymore, we should rather have a meta discussion than closing a single question for the wrong reason. – Dmitry Grigoryev Aug 29 '19 at 07:48
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    BTW, I replaced "etymology" with "terminology" which has a much wider use on this site. – Dmitry Grigoryev Aug 29 '19 at 07:56
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    Awesome answer in comment above by jonk about wood logs is etymology. Answers below especially one by marcelm, are terminology. IMHO removing etymology tag is wrong *if OP asked about the origins/history of expression* (which is not clarified). Definitely not opinion based, and great question. – temoto Aug 29 '19 at 16:42
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    I am specifically interested in the etymology. – daveloyall Aug 29 '19 at 20:16
  • Every buck converter lowers voltage AND raises current, right? (Ok, this is terminology.) Is the same true for every buck transformer? – daveloyall Aug 29 '19 at 20:17
  • I agree that @jonk's comment should be an answer. Based on that comment, I've decided to ask the radio show `A Way With Words` to settle this. – daveloyall Aug 29 '19 at 20:19
  • @daveloyall I think your question is very interesting. I [answered a question here](https://electronics.stackexchange.com/a/381906/38098) about how we wound up with the values seen in the E-series for resistors. That study took me in a very fun and interesting direction. I hope they choose to research and discuss your question to them. Let us know, somehow? (I didn't provide an answer because I really don't have a clue. I did learn some uses of "buck", recalling buckboards plus using a heavy hammer behind something pounded from the other side to add inertia -- both of which I've experienced.) – jonk Aug 29 '19 at 21:16
  • As promised, I've accepted the answer that matched [what the radio show said](https://twitter.com/wayword/status/1167566740261412865). (Though, their response was not particularly satisfying!) – daveloyall Sep 03 '19 at 22:08

5 Answers5

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It's the same sense as to "buck" a trend:

  1. to oppose or resist (something that seems oppressive or inevitable). "the shares bucked the market trend" synonyms: resist, oppose, contradict, defy, fight (against), go against, kick against "it takes guts to buck the system"

So you're "bucking" the input voltage to reduce the output voltage.

John D
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    Which is more applicable to transformers than to regulators, but the idea of "bucking" as "reducing voltage" probably came from transformer usage, and got transferred to regulator usage. – TimWescott Aug 28 '19 at 23:27
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    Buck regulators use an inductor which opposes the current flow when the switch opens. So it's just as valid as the transformer use. – gbarry Aug 29 '19 at 03:08
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    @gbarry Right, we don't call linear regulators "buck" regulators – slebetman Aug 29 '19 at 09:13
  • There is a deeper root. It comes from the action of the buck converter being similar to a bull's or horse's bucking, which throws the rider down. – Motomotes Aug 29 '19 at 21:17
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I may be wrong(apparently there is no way to qualify any answer here as correct), but I had always assumed that "buck" referred to an action similar to a "bucking bronco or bull". A buck converter sends a voltage pulse only as often as it needs to in order to provide the rectified and filtered DC output required, just as a "bucking bronco or bull" will "buck" as often as he feels he needs to in order to eject the rider or loosen the strap.

Hitek
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    Please, no downvotes because you dislike rodeos. Even though I understand where you may be coming from, it is a very plausible answer... – Hitek Aug 29 '19 at 02:32
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    (No one is downvoting?) I honestly thought it had to do with animals as well when I first heard the term but I knew that it probably wasn't correct. The verb "buck" could mean to be resistant against something. I think there could be a way to qualify an answer and that's looking it up in the dictionary :) –  Aug 29 '19 at 02:38
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    @KingDuken - I know, but right after I posted the answer I had visions of SJW bombardment, so I was just trying to preempt that :). If the term isn't derived from my suggested possible answer, than it does likely refer to resistance, as you say... – Hitek Aug 29 '19 at 02:42
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    Since most of the switching topologies work by making controlled pulses in response to operating conditions, it's hard to imagine that we'd take the "bucking" notion and specifically put it on the one that's a step-down. – gbarry Aug 29 '19 at 04:57
  • @gbarry - I sort of see it in the opposite scenario. An animal "bucks" as high and often as it need to in order to obtain it's goal, I see it as "providing action only to the extent that is required", rather than the dictionary version, which implies more of a "resistance" or "opposition" aspect, and would seem more analogous to the implementation in a linear regulator... – Hitek Aug 29 '19 at 05:16
  • @Hitek Not entirely sure why you would think that would invite "SJW bombardment"... – probably_someone Aug 29 '19 at 12:19
  • @probably_someone Because there are people out there who will take any technical (or other) non-controversial item and decide to turn it into a political/ideological war. It is stupid/crazy - on all sides. But it most definitely happens. I have seen it in comments on articles about Tesla (articles that are purely technical in nature) and many other places. – manassehkatz-Moving 2 Codidact Aug 29 '19 at 16:48
  • @manassehkatz Who are you to decide what is "non-controversial"? Why is your definition of the term better than someone else's definition? In any case, pre-emptively assuming and making a point of saying that you expect this to happen to your comment either a) makes it look like you're looking for a way to be the victim, or b) makes it look like you're purposely trying to get a rise out of people. Neither is a particularly good look. – probably_someone Aug 29 '19 at 16:51
  • @probably_someone Everyone has their own definition of "controversial". My point is that I see (as Hitek was concerned) far too often where a *technical* or similar posting/article/etc. that is clearly not intended to make a political statement gets "hijacked" in responses to become a political item. The specific example here is, I believe, typical - concern about some people taking references to rodeos (quite arguably abusive treatment of animals - I'm not disputing the problem and neither is Hitek) and turning it from merely "source of a term" and having the purely technical answer become... – manassehkatz-Moving 2 Codidact Aug 29 '19 at 17:04
  • a target for anyone who dislikes (for any reason) rodeos. In other words, Hitek's mention of *rodeo* should not become a license for people to downvote and/or complain about Hitek. But that type of behavior has become all too common on many sites. Thankfully not so much on StackExchange, as moderators (and long-time members) generally do a good job of keeping things on track. – manassehkatz-Moving 2 Codidact Aug 29 '19 at 17:07
  • @manassehkatz Three questions: 1) Why does an article being technical prevent it from being controversial? For example, at least in the US, virtually any research paper published in the field of climate change is controversial. 2) How do you know the intent of the author? In particular, how do you know the intent better than the people who are objecting? 3) Why is the lack of intent a complete exoneration of the author? I could see it as a mitigating factor, at best. Ultimately, aren't people supposed to be at least somewhat responsible for the consequences of what they say? – probably_someone Aug 29 '19 at 17:16
  • "climate change" is a perfect example. I **expect** an article on climate change (whether supporting or denying it) to elicit comments (supporting or opposing the claims of the paper *or even semi-related issues like **consequences** of climate change when the article is more about causes, etc.*. That is **normal**. What is not normal, IMHO, is, for example, someone to take an article about technical aspects of Tesla (just to use a very high-profile example) - e.g., latest features like Summons or Sentry Mode or whatever *that have nothing inherently to do with climate change* and then... – manassehkatz-Moving 2 Codidact Aug 29 '19 at 17:24
  • simply because "Tesla as a company relates to controversial topics" get into a discussion of climate change (which Tesla/Elon Musk certainly have a lot to do with). In other words, put the "discussion of controversial items" where it belongs. To use the immediate example here, if Hitek said "go to a rodeo and see what they do, ain't it awesome, that's what 'buck' converters do" would be an invitation to downvotes/comments/criticism/etc. But a simple statement of "I think this is where the word 'buck' comes from" **should not, IMHO, be controversial**. End of my part - I'll stick to technical. – manassehkatz-Moving 2 Codidact Aug 29 '19 at 17:27
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    Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/98048/discussion-between-probably-someone-and-manassehkatz). – probably_someone Aug 29 '19 at 17:37
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Question probably belongs on english.stackexchange.com. It arises from bucking being an action an animal takes to throw riders off or down, so a buck converter "throws" the voltage down by a repetitive "bucking" mechanism.

buck (v.1)

of a horse, "make a violent back-arched leap in an effort to throw off a rider," 1848, apparently "jump like a buck," from buck (n.1). Related: Bucked; bucking. Buck up "cheer up" is from 1844, probably from the noun in the "man" sense.

(from etymonline.com)

chicks
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Motomotes
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Step-down converters is really a subclass of DC-DC converters, while a buck converter is one specific topology ("brand") of step-down converter. In essence, a buck converter is a step-down converter, but not every step-down converter is a buck converter. In theory, anyway.

Let's look at an overview of the various non-isolated DC-DC converter topologies:

Step-down

Step-up/down

Step-up

As you can see, the subclasses are step-up, step-down, and step-up/down, and there are some topologies in each subclass. You can also see that there's only one topology in the step-down subclass: the buck converter. So:

But, why is a step-down converter called a buck converter?

Because buck converters are step-down converters, and in practice all step-down converters are buck converters. The names refer to different things, but in practice it doesn't matter, so they're used interchangeably.

The Texas Instruments book Power Topologies Handbook (by Markus Zehendner and Matthias Ulmann) also has a good overview of the various topologies (also including isolating converters).

If you want to know where the name "buck converter" comes from; I don't know, but the other answers try to address that.

marcelm
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The buck converter is so named because the inductor always “bucks” or acts against the input voltage.

The Wash Doc
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