Suggestions on DC converters - Page 1
Forum section: electronics / projects

author: vgamesx2
author_rank: Regular Contributor
timestamp: March 23, 2016, 08:54:57 pm
content: Hello, can someone recommend a good dc converter or even just an IC to build my own? I'm looking for something like these LTC3780shttp://r.ebay.com/8FVv4pI have a solar setup charging 12V batteries, so I want both the boost and buck operations for 1V-30V but I also want current control to limit the drain on my batteries and also to use it as a bench power supply.(oh and I need it to provide up to 5A)However, I've had a difficult time trying to find an alternative other than a few ICs such as the LT3791-1, any suggestions? Thanks

author: Buriedcode
author_rank: Super Contributor
timestamp: March 23, 2016, 11:12:28 pm
content: I think you'll get more replies if you're more specific with your requirements. From what I can gather you want this:Solar panel array (1-30V) -> 12V SLA -> 5A bench power supply (voltage range?).Firstly, your solar array, it is unlikely that a solar array will kick out 1V, but will vary its voltage and current based on the sun. So I would work out the practical maximum and minimum for that.Secondly, what capacity is your 12V battery? is it gel, SLA?Thirdly, what voltage range does your bench PSU have to have, how many channels, and is it just voltage, or CC/CV with set limits?The bench top power supply, well there's plenty of designs for those floating around, so I guess its just the buck/boost part for the charger.You *could* use that device linked, but it seems rather powerful, so I'm assuming you have a large 12V battery and a large solar array. Otherwise if you're getting 100mA from your solar array, your battery will take an age to charge.

author: vgamesx2
author_rank: Regular Contributor
timestamp: March 23, 2016, 11:58:00 pm
content: Quote from: Buriedcode on March 23, 2016, 11:12:28 pmThanks for the reply and sorry about the misunderstanding, let me clarify...I have a 35W solar panel > charge controller > charges two SLA 12V batteries in a 1S2P configuration with 10Ah each or 20Ah total > then DC converter > my loadI mainly like to use it to charge my phones or battery banks so I need 5V out but I would also like to charge my laptop at 19V and I also have a few things like a hakko 936 clone handle I used to make my own soldering iron that takes upwards of 24-30V at 3A so I need a wide voltage range of at least 3V-25V for everything I want to use it for, including dual purpose as a bench power supply and adjustable CC down to about 100ma or so would be nice.I actually don't want charge my SLA batteries but instead, I like to keep them topped off and use them sort of as a giant capacitor to charge my other devices or batteries, that's the main reason I need CC so I can limit the power output to about 15W or roughly what the solar panel is producing.

author: Probb
author_rank: Contributor
timestamp: March 24, 2016, 12:51:20 am
content: If you're willing to dig a little deeper into designing your own converter, I'd recommend starting with the LM5175 Buck-Boost Controller, combined with BUK9Y7R2-60E N-MOSFETS:http://www.ti.com/lit/ds/symlink/lm5175.pdfhttp://www.nxp.com/documents/data_sheet/BUK9Y7R2-60E.pdfThe FETs should be capable of handling the power you're dealing with, and the controller IC has the current limiting capabilities. Really comes down to your inductor size at the switching output.There's plenty of dual channel controller IC options out there to get multiple voltage outputs simultaneously; however, you're somewhat limited to buck OR boost operation in this case.Of course, if you size your inductor properly to meet your load requirements, all you really need to do is incorporate switching frequency control for the converter (keeping in mind continuous and discontinuous current modes throughout switching frequencies) to vary voltage output levels.

author: vgamesx2
author_rank: Regular Contributor
timestamp: March 24, 2016, 02:30:01 am
content: Neat I quite like that one, especially since the efficiency peaks at just over 98% within battery voltage, awesome!The only issue I have with building one is that I'm still fairly new to electronics, I've gotten the basics down, so I know what most of the components are and what they do and I can sort of read schematics ok-ish but I don't fully understand how the components interact with each other yet, so yeah anything much beyond a common LM317 is starts to get little too complicated for me.(also I don't have an oscilloscope, so troubleshooting is going to be a big issue if I screw up.)Thanks for the suggestion though, I'll look into it and see if I might be able to use it.

author: Probb
author_rank: Contributor
timestamp: March 24, 2016, 04:14:31 am
content: Step-by-step man, it's all fun and games.If you're after something a bit more quick and dirty, eBay is always your friend:http://www.ebay.com/bhp/buck-boost-converter

author: Probb
author_rank: Contributor
timestamp: March 24, 2016, 04:21:52 am
content: And, if you're looking for some reading material that might put you to sleep tonight, this is a pretty decent tutorial on switch-mode converter fundamentals (in case you want to dig into designing your own supply down the road):https://www.maximintegrated.com/en/app-notes/index.mvp/id/2031

author: vgamesx2
author_rank: Regular Contributor
timestamp: March 24, 2016, 04:49:26 am
content: Quote from: Probb on March 24, 2016, 04:14:31 amYeah sure but just nothing quite matches what I'm looking for, they always manage to miss something I'm after, for instance here's the best alternative I've managed to find thus farhttp://r.ebay.com/ULcv6xWhich uses an XL6019 it would be perfect and it even has programmable voltage via the pins next to the input terminal except... No CCSo yeah I suppose if I don't build it myself I'll just get a sperate boost and buck converter, either that or try my luck with yet another LTC3780.Quote from: Probb on March 24, 2016, 04:21:52 amHaha, I could certainly use something to help me fall asleep, I end up staying up way too late half the time lol. Cheers

author: Buriedcode
author_rank: Super Contributor
timestamp: March 24, 2016, 11:18:01 am
content: Righty. 15W panel, 35W max, two 12V 10Ah batteries. And you'll need 19v @ 3A, 5V out (USB 3.0 spec power? 2A), 3-30V @ 3A out.Regardless of your level of electronics, breaking it down into modules in a diagram helps a great deal. I imagine you could easily find 'modules' on ebay that will do the work for you, as you've been looking anyway, plus... it generally works out much cheaper (for the price of some of these converters, it costs less than the parts if you were to build yourself, plus, no hassle).Solar Panel to keep two 12V batteries topped up. If they are only 15W then you might be able to get away with a linear charger. A switching controller would be nice but can be a hassle. I suspect this will be something you'll have to build yourself. The XL6019 can do buck/boost (I believe its actually a sepic converter, but they don't call it that in the datasheet). Making your own with this requires a PCB to be designed, and made - if you're at the 'LM317' stage of electronics, this could be a bit of a struggle, plus, ordering a few PCB's is added costs. So I would suggest this:http://www.ebay.co.uk/itm/LM2577S-LM2596S-DC-Step-Up-Down-Boost-Buck-CC-CV-Voltage-Converter-LED-Driver-UK-/281777880409?hash=item419b453d59:g:zeQAAOSwPcVVwlPaThe efficiency isn't the best, and it probably has fairly crap current regulation, but sohuld be fine for battery charging. You'll have to power it up, put a load across it, and turn the pot's to set the current limit, and the voltage limit (voltage limit should be ~14V for 12V SLA, or set to 13.8V for constant trickle charge). It's just a buck and a boost on one board which isn't the best way, but its cheap, has CV, CC, and easy to use.For 19V @3A for your laptop -http://www.ebay.co.uk/itm/Max-5A-LM2587-Step-Up-Boost-DC-Regulator-Converter-Inverter-HW-/222056503254?hash=item33b39957d6:g:2H4AAOSw-W5UywM9http://www.ti.com/lit/ds/symlink/lm2587.pdfis the device used. This can also be used with a coupled inductor (1:1 transformer essentially) so it could also be used for your solar charger, as the example circuit is 8-16V in... 12V out (you can adjust that to 14V).For 5V @ 2A out for phone/tablet charging:http://www.ebay.co.uk/itm/MP1584-3A-DC-DC-Buck-Adjustable-Converter-Step-Down-Power-Supply-like-LM2596-/141866735563?hash=item2107ea97cb:g:13kAAOSwNSxU1lcuI have used these, they do the job, but do get warm for > 2A. It isn't very robust and the SMD pot is a bit flimsy.http://www.ebay.co.uk/itm/7V-24V-to-5V-3A-DC-DC-Step-Down-Buck-Converter-Module-to-USB-Output-KIS3R33S-UK-/400865889524?hash=item5d55780cf4:g:jUcAAOSwcnpToC3Lthat might be better. Easier to work with as it already has a USB socket (probably rather cheap).The trouble with charging from USB is often you'll need to wire the D+/D- lines in a way (both to GND?) to indicate to the phone what the power capacity of the host is. It'll default to charging at 500mA (max for USB 2.0 spec), you'll have to check how you tell the device the socket is capable of 2.0A. If you have apple products, this is apparently more complicated.Finally, your soldering iron 3-30V @ 3A. I believe the 'buck boost' module linked above would do that, although for a temperature controlled iron, you'll have to make the regulation circuit yourself. Might be easier to just buy a cheap temp-regulated iron that runs on a fixed DC voltage, and use that.It'll be complicated, by I'm fairly sure most of it can using modules and wiring it up with their screw terminals. Hate to admit it, even though many of these ebay modules aren't as great as their sellers make out (they always quote peak efficiency and best output ripple) they generally get the job done and for a fraction of the price it would cost me to make my own. I have modded some of them with better caps, and more precise resistors to fix the output voltages but often that isn't needed.

author: vgamesx2
author_rank: Regular Contributor
timestamp: March 24, 2016, 05:05:29 pm
content: I think you still sort of didn't get what I meant with the solar panel, I have a cheap PWM charge controller charging the SLA batteries, so I don't need anything else to charge them, although it could be a fun project to get one of thesehttp://r.ebay.com/F7Y1opthen modify it with a digital potentiometer and an ardunio or whatever to make it true MPPT.I've considered getting one of those LM2596S based converters, the only thing I don't like about them is that they boost up to 30V then buck down to what you want, so that's quite wasteful and not great when you're running stuff off small batteries, but I may get one anyway just for CC."You'll have to power it up, put a load across it" Lol I usually just short them out with my DMM, should I not be doing that?I like the recommendations although I already have a 5V solution, I have one of these encapsulated modules, basically about the same thing but you can't adjust it.http://r.ebay.com/ld4dNGIt works great though and I tested it with one of those USB testers and it outputs 2A out of the box, I mainly just wanted 5V output as a second access point if I needed it or for breadboard use.Lastly, I just wanted to point out that my iron IS temperature controlled, I got a controller along with the handle.http://www.aliexpress.com/item/Use-the-936-transformer-Soldering-station-controller-circuit-board-for-digital-A1322-T12-T2-Heating-Core/32339964077.htmlThus far I've not really used it, I've only tested the iron to get warm, but it should work, right now I'm working on a wooden box for everything and yeah I agree it's amazing just how you can get these little pre-made modules for next to nothing, even though they tend to hide some of the more in-depth details about what they're selling it's still a great value.(oh especially on Aliexpress, as you can get certain things such as the AMS1117 regulators for a mere 3-5 cents each or a single piece of perf board for 20-30 cents.)

author: technix
author_rank: Super Contributor
timestamp: March 24, 2016, 05:10:40 pm
content: For the beginners, I would suggest MC34063, as it is cheap, versatile, easy to prototype and did I mention cheap?If you want something more advanced I would suggest using a small MCU as a SMPS controller and use external MOSFETs to switch the current. This means a few power MOSFETs, an Arduino board (or a few ATtiny85's - those little bastards have an internal PLL that can run at 16MHz with PWM frequency at ridiculous high speeds like 250kHz and 500kHz, all without any external clock source!) and maybe a gate driver chip like the IR2101.

author: Seekonk
author_rank: Super Contributor
timestamp: March 24, 2016, 05:34:02 pm
content: Any buck converter can be converted easily int a power point controller for solar. Just set the output at the max battery voltage, most active systems never get out of bulk. Then monitor panel voltage with something as simple as zener pot and transistor. Under voltage fakes the feedback sense into thinking output is too high shutting down conversion. Fixed power point is sufficient for most applications. Tracking can be done with a couple diodes in series attached to back of panel. That thermal reference into a comprator will allow it to track.

author: vgamesx2
author_rank: Regular Contributor
timestamp: March 24, 2016, 05:54:28 pm
content: Quote from: technix on March 24, 2016, 05:10:40 pmNeat, I immediately found some for $1 at that price I'll have to get some even if I don't actually end up using them, I like cheapQuote from: Seekonk on March 24, 2016, 05:34:02 pmWow that's quite interesting, I had no idea you could do that although I don't know what a zener pot is, can you explain?

author: Seekonk
author_rank: Super Contributor
timestamp: March 24, 2016, 07:22:52 pm
content: 34063 YUCK.I had this old picture handy and it shows basic principle. Note some parts can be eliminated if a 12V panel. This shows enable pin on 2596 module which is quite fast. Similar thing can be done with feedback.

author: vgamesx2
author_rank: Regular Contributor
timestamp: March 24, 2016, 08:32:03 pm
content: Cool, I'll probably give it a go at some point.

author: technix
author_rank: Super Contributor
timestamp: March 25, 2016, 03:10:45 pm
content: Quote from: Seekonk on March 24, 2016, 07:22:52 pmCare to elaborate why?