Boost converter vs Buck Converter? - Page 1
Forum section: electronics / beginners

author: ElectricPower
author_rank: Frequent Contributor
timestamp: December 09, 2019, 12:05:53 pm
content: Sorry if this question is really stupid, but I wonder why you should choose a "Boost converter" rather than a "Buck Converter".What are the advantages and disadvantages and what should you choose if you live on a budget and can only buy one of the parts?

author: wraper
author_rank: Unknown
timestamp: December 09, 2019, 12:10:55 pm
content: Boost converter increases voltage. Buck converter decreases. Choose depending on what you need to do.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 09, 2019, 12:11:02 pm
content: Boost boosts the voltage (Vout > Vin), buck bucks the voltage (Vout < Vin). Output is always common-ground and same sign as input.What parts would you only be able to buy one of? Complete modules are a few bucks (not that they're any good).If you need a more universal option, perhaps a SEPIC converter would do (Vin <=> Vout)? These are likely to be more expensive though.Things get very unwieldy (component cost, efficiency) for wide ranges of input or output, hence why converters are usually made in many models to suit each range. You wouldn't use a 48V or 3.3V converter at 12V (indeed, they might be physically incompatible).Edit: which, well, there you go, they do indeed make them, as crusty as ever but not much more expensive as it turns out:https://www.ebay.com/itm/92-Efficiency-LM2577-SEPIC-Adjustable-3-35V-To-1-2-30V-Charging-Power-Regulator/312598343651?epid=5025061872&hash=item48c8502fe3:g:c-AAAOSwUUhc0EFSTim

author: ElectricPower
author_rank: Frequent Contributor
timestamp: December 12, 2019, 03:19:10 am
content: Ok, i know the main difference between them. Buck is down and boost is up. Easy peacy so far...But let's say i need som random power in my workshop from time to time between 0-30 volt and 0-10 amps to give the right amount of power for my projects. When do i know to choose right between a buck og boost converter?Both converter types works, but why should i choose the one over the other?

author: BravoV
author_rank: Super Contributor
timestamp: December 12, 2019, 03:30:42 am
content: So called "buck-boost" topology also exist, it has both.

author: ElectricPower
author_rank: Frequent Contributor
timestamp: December 12, 2019, 03:49:43 am
content: Yes, i know.But what to choose and why?For my projects i think a simple LM2596 will work 90% of all my projects. I also have an Amptek 0-30/10amp adjustable power supply with some more juice, so i think i am well covered, but i still wonder why i should chose a buck/Boost converter.Is there som advantage/disadvantage besides that the one boost the power and the other steps it down?

author: JxR
author_rank: Unknown
timestamp: December 12, 2019, 03:52:52 am
content: Which one you choose really just depends on the source voltage you have and the output voltage you need. As to which one is better, well one thing to keep in mind is when boosting the source supply is going to draw more current than the output.-Say you need 9V@1.5A output, so 13.5W of power output. The efficiency of your boost converter is 85%.-You have a 2x AA to provide the input power: 13.5W / (1.5V * 2) / 0.85 = ~5.3A of current is needed from your 2x AA. As the batteries drain, their voltage lowers and the current draw required increases as well.You can see that this is completely unrealistic for 2x AA to provide this amount of power. I guess you might consider this a disadvantage of using a boost converter. At the very least it is something you have to keep in mind.

author: atmfjstc
author_rank: Regular Contributor
timestamp: December 12, 2019, 04:58:03 am
content: If you think about it, a question about buck vs boost can be rephrased as a question about batteries. If you can choose between buck or boost, that must mean you have some control over the raw input voltage of your project, which usually means being able to put more or fewer batteries in series, or choose between AA/NiMH (~1.2V/cell) and Li-Ion (~3.7V/cell).With that perspective in mind, one can see that the limitations of batteries can easily force you into one choice or the other.As an example, if your project needs 5V and all you have is NiMH cells (which go from about 1.4-1.1V over a decent discharge), you can either:a) power it with 1 to 3 batteries in cells and use a boost converterb) power it with more than 5 batteries in cells and use a buck converter(there are other options but let's not get lost in the details)With option a), the fewer cells you use, the more current will be drawn from each cell (a lot more). If you project needs a lot of power, even 3 cells might not be able to handle it, in which case you'll be forced to either use option b), or add another string of cells in parallel (which comes with its own set of problems).Even if the cells can take it, more current means more problems. The converter will be less efficient the wider the gap between the raw and output voltage. Cells become more inefficient the higher their discharge current. If the batteries are also not immediately adjacent to the converter (can happen with some robots), high current and low voltage means a significant voltage loss in the battery wires, which further decreases efficiency.One significant advantage of option a), however, is that you can get away with using the minimal number of batteries if you don't need too much power. This can be critical in weight-sensitive applications like small robots.Option a) has the advantage of using fewer batteries, which can be critical in a weight-sensitive application like a robot.With option b), the current is reduced the more cells you place in series. This means less stress on each individual cell, better performance from the batteries, reduced losses, less heat. Overall this can add up to massive efficiency gains. I was once able to significantly (20-30%) boost the runtime of a battery-operated Raspberry Pi by switching from 4s2p NiMH with a boost converter, to 8s with a buck converter.One major disadvantage of using a buck converter is that there are some designs out there have a deadly failure mode where the full raw input voltage will be present at the output. You'll want to provide some protection downstream from the converter to ensure your expensive circuit isn't destroyed if the converter malfunctions.

author: james_s
author_rank: Super Contributor
timestamp: December 12, 2019, 06:36:48 am
content: Generally speaking, buck converters are more efficient, the input current is lower for a given wattage, the switching device and inductor run cooler and have lower losses all else being equal.

author: ElectricPower
author_rank: Frequent Contributor
timestamp: December 12, 2019, 07:55:08 am
content: Ok, i think i understand what you meaning.When it comes to batteries i do not use that at all. I only use my power supply home in basement and i have it connected to 220V/16amp socket in my house. I think a buck converter plugged inn with a kick ass power supply practically will do the same job as mine adjustable power supply.Whether the power is being stepped down or up is for me same shitAs long i have an 220V/16amp socket i guess that and my boost supply will be the best choice...?Btw: I hope you understand my english. I'm an white and cold guy from Norwegian thats understand english perfectly, but to write and make other understand me, is not my strongest side

author: mariush
author_rank: Super Contributor
timestamp: December 12, 2019, 09:37:40 am
content: In some scenarios, you'd want to avoid using a switching power supply to power your circuit, because the output of a buck or boost converter isn't a very smooth voltage, it has ripple and noise.For example when developing a microcontroller that makes measurements using its ADC, the noise from buck regulator could affect the ADC measurements.That's one of the reasons why adjustable power supplies in the past used big transformers and pass transistors, basically those worked like linear regulators, outputting smooth voltage with minimal ripple.

author: ElectricPower
author_rank: Frequent Contributor
timestamp: December 12, 2019, 01:43:26 pm
content: Whitch power supply do you recommend? Link please?