More modern LM2596 5V DC-DC converter - Page 1
Forum section: electronics / projects

author: ilium007
author_rank: Frequent Contributor
timestamp: November 07, 2020, 05:14:50 am
content: I have been researching 5V DC-DC converters and people keep stating that the 150kHz LM2596 converter is now ancient and belongs in the bin.I am trying to build a 5V DC-DC converter to put on a bunch of boards I am designing. The first board will take a 24VAC feed (garden solenoids), half wave rectified to the DC-DC converter to get 5V.I found the attached schematic athttps://openthings.io/24vac-to-5vdc-conversion/Is there a better IC that I should be researching or is the LM2596 good enough in 2020?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 07, 2020, 06:13:21 am
content: So what, same ratings, newer product? No particular EMI or size requirements?Cost?If you look at the datasheet, it seems they already recommend an update:https://www.ti.com/product/LMR33630?HQS=ds-snvs124-lmr33630-feat-pfThe SIMPLE SWITCHER line has plenty of updated parts; the Eco-mode family seems fine, too (usually TPS54xxx?).Tim

author: ilium007
author_rank: Frequent Contributor
timestamp: November 07, 2020, 06:17:24 am
content: I’ll take a look at the replacement. Cost isn’t really an option, these boards are for personal projects. I just want to sink my time into the right component.

author: Unixon
author_rank: Frequent Contributor
timestamp: November 07, 2020, 07:49:56 am
content: TPS54340/TPS54540 and alike, work like magic, cold at rated current.

author: ilium007
author_rank: Frequent Contributor
timestamp: November 07, 2020, 08:12:19 am
content: Quote from: Unixon on November 07, 2020, 07:49:56 amThanks! Its going to take me a month to get through that datasheet!

author: sandalcandal
author_rank: Unknown
timestamp: November 07, 2020, 11:11:02 am
content: If you just need a simple stock standard power supply there are lots of tools by vendors to automatically spit out the best offerings in their product line ups complete with a configured circuit and some will even spilt out a simulation, thermal analysis, example PCB layout and fully costed BoM:https://www.ti.com/design-resources/design-tools-simulation/webench-power-designer.htmlhttps://www.st.com/en/applications/power-supplies-and-converters.html#tools-softwarehttps://www.analog.com/en/design-center/ltpowercad.htmlhttps://infineon.poweresim.com/index.jsphttps://www.onsemi.com/support/design-tools/inputsProbably more I missed and some vendors don't have an automated tool. Pick your favourite brand or try them all if you really want the best on the market. Keep in mind they're ultimately marketing tools for the vendors and TI's webench is probably the most featured and easiest to use...Edit: I'm pretty sure Webench has the TPS54340/TPS54540 if you're already set on using it and just need a quick reference.

author: wraper
author_rank: Unknown
timestamp: November 07, 2020, 11:16:33 am
content: Quote from: ilium007 on November 07, 2020, 05:14:50 amIf your circuit has such low supply current that you can use one diode with 100uF cap for rectification, you'd be completely fine even with MC34063.

author: ilium007
author_rank: Frequent Contributor
timestamp: November 07, 2020, 11:45:00 am
content: Quote from: wraper on November 07, 2020, 11:16:33 amIts an example circuit I found. I was planning on running a full bridge rectifier prior to feeding into the DC-DC converter.

author: ilium007
author_rank: Frequent Contributor
timestamp: November 07, 2020, 11:59:26 am
content: Quote from: sandalcandal on November 07, 2020, 11:11:02 amThanks - great set of tools.

author: poorchava
author_rank: Super Contributor
timestamp: November 07, 2020, 04:15:43 pm
content: I tend to use TI converters due to quite useful online tool and broad range of chips. Beware though, the online tool has quite limited library of external components, and the choices of diodes for example are sometimes nonsense. For more obscure/weird design requirements AD/Linear and Maxim often have some solutions, though in case of Maxim there might be problems with availability of larger quantities of chips.

author: WattsThat
author_rank: Frequent Contributor
timestamp: November 08, 2020, 03:09:35 am
content: Also be aware that most of the LM2596’s sold through the usual Chinese sources are counterfeit/cloned products. Why mess about with unknown parts that while they may work, they’re likely sub-spec in some way. Right up there with the FTDI232 and MAX3232 parts.We should ask Noopy to de-cap some of the LM2596’s on those $1 buck converter boards, it would be interesting to see what’s inside.

author: poorchava
author_rank: Super Contributor
timestamp: November 08, 2020, 11:32:13 am
content: /offtopic: that's why I use FT230X, they are not getting counterfeited as far as I know. RS232 is pretty much dead, so max232 is not that relevant anymore.Microchip also does some nice converters, which are usually cheaper than TI, but somewhat limited in terms of voltages and currents. For very low voltages, Alpha and Omega semiconductor make some nice and easy to use switchers.Another nice converters that I use a lot is ST1S10.

author: Unixon
author_rank: Frequent Contributor
timestamp: November 08, 2020, 01:57:42 pm
content: Quote from: poorchava on November 08, 2020, 11:32:13 amThis one is a killer, infamous for having failure mode that shorts the output to the input frying everything on its low side.It is pretty efficient in normal operation, but requires beefy TVS for load protection.

author: ilium007
author_rank: Frequent Contributor
timestamp: November 10, 2020, 09:39:32 pm
content: The ST1S10 only has a max 18v supply voltage.

author: Hiemal
author_rank: Regular Contributor
timestamp: November 10, 2020, 10:13:19 pm
content: https://www.ti.com/lit/ds/symlink/lmr16030.pdf?ts=1605046324212And its lower current sibling, LMR16020 are both good and very easy to use.

author: Renate
author_rank: Super Contributor
timestamp: November 11, 2020, 11:43:38 am
content: Quote from: WattsThat on November 08, 2020, 03:09:35 amA week ago I sent Noopy some LM2596's to check out.Some of them were brand-new TI 2596's from DigiKey.Others were from a Taiwan manufactured USB hub that blew 12V straight through and fried everything.Afterwards they operated exactly on voltage.

author: sandalcandal
author_rank: Unknown
timestamp: November 11, 2020, 01:23:51 pm
content: Quote from: Renate on November 11, 2020, 11:43:38 amIs that the one from the dodgy "industrial" USB hub you posted before? Looking forward to seeing that!

author: Renate
author_rank: Super Contributor
timestamp: November 11, 2020, 04:43:12 pm
content: Quote from: sandalcandal on November 11, 2020, 01:23:51 pmMe too! Yeah, it's the StarTech "industrial" USB 2.0 7 port.

author: mariush
author_rank: Super Contributor
timestamp: November 11, 2020, 06:29:16 pm
content: Quote from: ilium007 on November 07, 2020, 05:14:50 amHere's some optionsAOZ1282 (max 36v input, 450kHz switching, 1.2A max) :https://www.digikey.com/en/products/detail/alpha-omega-semiconductor-inc/AOZ1282CI/3973644MP2459 max 55v input 480khz etc :https://www.digikey.com/en/products/detail/monolithic-power-systems-inc/MP2459GJ-Z/9555319rt6266 , max 36v but only 100khz :https://www.digikey.com/en/products/detail/richtek-usa-inc/RT6266GSP/5880489ap64500, max 40v in, up to 2.2 mhz (min 100khz) , up to 5ahttps://www.digikey.com/en/products/detail/diodes-incorporated/AP64500SP-13/10419714and others:https://www.digikey.com/short/z03qf5

author: opampsmoker
author_rank: Regular Contributor
timestamp: November 11, 2020, 09:54:46 pm
content: ~32V to 5V conversion at a couple of watts?Use a coupled sepic converter every time.....low side drive, low side current sense.And.....Just use your favorite simple current mode controller...eg UCC28C43 etc.Just make sure the res freq between your Lleak and Csepic, is not higher than the switching frequency, else you'll get a hot coupled inductor...coilcraft do a good range of offtheshelf coupled inductors... also wuerth, and some others.Designing it is bascially like a one to one flyback....in fact , youll see the fet and diode currents are exactly the same as what you get in a 1:1 flyback

author: langwadt
author_rank: Super Contributor
timestamp: November 11, 2020, 11:52:40 pm
content: Quote from: opampsmoker on November 11, 2020, 09:54:46 pmbut why? to triple the BOM?

author: opampsmoker
author_rank: Regular Contributor
timestamp: November 12, 2020, 08:22:32 am
content: its nice easy components...the LM2956 is very expensive...ucc28c43 is cheapHere is the coupled sepic attached in a LTspice simulation........by the way for 32v to 5v you wont need the slope comp, so yours is even easierLTspice is free....just open the file and hit run

author: ilium007
author_rank: Frequent Contributor
timestamp: November 12, 2020, 10:55:43 am
content: I've been looking at the LMR16030 on WEBENCH and then found another project where someone has a published design -https://www.electronics-lab.com/project/60v-5v-dc-dc-step-converter-using-lmr16030/.I notice on the WEBENCH design they show 2 x 68uF ceramic caps on the output but on the other design they have 2 x 10uF caps, one ceramic and one electrolytic. Why is this? I have notice on other power supply designs there seems to be a mic of electrolytic / ceramic caps on the outputs.

author: ilium007
author_rank: Frequent Contributor
timestamp: November 12, 2020, 11:04:13 am
content: This is another example using the ROHM BD9G341AEFJ, output has 2 x 47uF caps, one electrolytic and one ceramic.

author: sandalcandal
author_rank: Unknown
timestamp: November 12, 2020, 11:16:52 am
content: Generally a mix of MLCC and electrolytic capacitors is used to produce more cost effect output filtering. MLCC is more expensive than electrolytic per uF but (cheap) electrolytic caps tend to have much higher ESR which limits their ability to filter smaller and high frequency ripple. By combining the two, MLCC can provide filtering of high frequency ripple and the electrolytic can provide bulk filtering and the overall system cost can be reduced (potentially).As for why WEBENCH recommends two very large MLCC, I can't say for sure but it's likely to be a "just works" solution rather than something highly cost optimised but potentially unstable or out of spec. Determining optimal (minimal cost) output filtering is one of those black-magic areas of power electronics AFAIK. Simulation is possible but it's quite common to leave in extra pads to add/remove extra capacitance until an optimal design can be tested/verified on the bench (and in the field).

author: ilium007
author_rank: Frequent Contributor
timestamp: November 12, 2020, 12:19:06 pm
content: Ouch... I didn't realise they were that expensive!

author: ilium007
author_rank: Frequent Contributor
timestamp: November 12, 2020, 12:22:02 pm
content: Where is the best place to buy here in Australia for hobby quantities of SMD components?

author: sandalcandal
author_rank: Unknown
timestamp: November 12, 2020, 12:25:03 pm
content: Quote from: ilium007 on November 12, 2020, 12:19:06 pmThey're usually not quite that bad, that's one with metal frame leads and quite high voltage. You could use something like this:https://au.mouser.com/ProductDetail/Samsung-Electro-Mechanics/CL21A106KPFNNNGEdit: That's 10V rated so only for the output side

author: sandalcandal
author_rank: Unknown
timestamp: November 12, 2020, 12:33:45 pm
content: Quote from: ilium007 on November 12, 2020, 12:22:02 pmHard to beat the big suppliers for cost effectiveness and quality but unless you can hit the minimum order cost for free delivery it can be more expensive. RS components doesn't have a minimum for local stock though so they can be pretty good if you only want small ordershttps://au.rs-online.com/Buying in bulk and larger consolidated orders will pretty much always be cheaper.For hobbyist tools, modules and kits I quite like Little Bird for ordering local in Ozhttps://www.littlebird.com.au/but for discrete components I find it better to go to suppliers.

author: mariush
author_rank: Super Contributor
timestamp: November 12, 2020, 12:35:02 pm
content: Quote from: ilium007 on November 12, 2020, 12:19:06 pmYou don't need 100v rated ceramic capacitors on the output, unless the output of your regulator is something like 24v..48vIf you have 32..40v in, 5v out, then you can do with some decent 25v...50v rated x7r capacitors... a couple 10-22uF in parallel would probably be enough.Even with a higher voltage output, you would probably be fine with a hybrid polymer-tantalum or a polymer (solid) capacitor in parallel with a small 1uF .. 4.7uF ceramic capacitor.As for input capacitors, most I suggested should be fine with an regular low esr electrolytic capacitor, maybe paralleled with a 0.1uF - 1uF ceramic capacitor. If you know for sure your input voltage will be low enough then a solid (polymer) 25-35v rated capacitor would be plenty.The higher switching frequency regulators use much smaller inductors, which are cheaper, and they also have mosfets integrated do often all you need is the inductor, a schottky diode, output capacitor and optional resistors to set output voltage (if the regulator is not fixed output voltage) ... so the chip may cost more but you're saving money in the inductor and other smaller and fewer surface mounted components. With some of those regulators you also don't have to deal with compensation networks, having to choose uncommon ceramic capacitor and resistors values to get a chip working for a specific input - output voltage / current combination

author: Renate
author_rank: Super Contributor
timestamp: November 12, 2020, 12:41:20 pm
content: Quote from: poorchava on November 07, 2020, 04:15:43 pmI was playing with TI's design tool and I was surprised to see that all the designs coming back at me were all synchronous.Not a diode in sight.It's astounding to see how many chips from different series come back for "garden variety" (12V - 5V) buck applications.

author: sandalcandal
author_rank: Unknown
timestamp: November 12, 2020, 12:56:34 pm
content: Quote from: Renate on November 12, 2020, 12:41:20 pmA huge market and a shed load of money to be made in that application space/market segment no doubt...

author: thinkfat
author_rank: Unknown
timestamp: November 12, 2020, 12:57:29 pm
content: WBENCH can optimize the design in different directions, board area, BOM cost, unique items. Maybe play around a bit.

author: Ian.M
author_rank: Super Contributor
timestamp: November 12, 2020, 01:14:16 pm
content: The only reason for the evil reputation LM2596 now has is the cheap Chinese fakes. I'm not even going to call them clones since they seem to be based on a clone of the older ~52KHz LM2576 (as opposed to 150KHz for the genuine chip). The issue with cheap 'LM2596' DC-DC converter modules is if they use the fake chip it needs three times as much inductance and reservoir capacitance to give similar performance (but probably still inferior) to a genuine LM2596, but the values used by the module manufacturers are typically three times too small as they were chosen for the genuine chip. This means the 3A max of the genuine chip derates to 1A max, and the poor thermal management derates that further till you are lucky if the module can deliver 500mA continuous without overheating. Others have mentioned their tendency to fail or glitch in ways that let through the full input voltage, so using them with a valuable load is at best unwise. Detecting them is easy - under load, either scope pin 2 of the chip with a probe rated for at least twice the supply voltage, or probe it with a DMM with a frequency range. Provided the load is high enough to prevent cycle skipping, if the frequency isn't approx 150KHz you've certainly got a fake. The converse isn't reliable as there may be high quality 150KHz clone parts out there.Due to its relatively low operating frequency (compared to more modern alternatives) a genuine LM2596 is pretty forgiving of poor layout - you can even build it up on protoboard and if you keep connections reasonably short, and pay attention to your loop areas, you'll get away with it with no issues, and if you effectively ground its tab (and heatsink if used) it wont even emit excessive EMI. Purchased as a chip from a major distributor, its still a good choice for aone-offproject if the size and weight of the required passives aren't a significant constraint.

author: thinkfat
author_rank: Unknown
timestamp: November 12, 2020, 01:48:28 pm
content: One, maybe the primary reason I went for the LM2676 and later LMR14030SDDAR were indeed board real-estate. I simply couldn't fit the inductor in the area I had.

author: opampsmoker
author_rank: Regular Contributor
timestamp: November 15, 2020, 09:03:16 pm
content: Attached is a nice 32v -> 5v buck converter.Sync Buck.It switches even in no load so the bootstrap cap stays charged.Coilcraft do suitable CSTs for this....and otherscst = current sense transformerLTspice sim and pdf schem attached

author: bizkits
author_rank: Contributor
timestamp: November 16, 2020, 08:59:46 am
content: I usually use the DC-DC from RECOM or Murata.Here are 2 which I have used before and I find them very good.All they need are a few capacitors as suggested in the datasheet.The footprint is also small.1.https://www.digikey.com/en/products/detail/recom-power/R-78E5-0-1-0/49305852.https://www.digikey.com/en/products/detail/murata-power-solutions-inc/OKI-78SR-5-1-5-W36-C/2259781

author: ilium007
author_rank: Frequent Contributor
timestamp: November 16, 2020, 10:03:46 am
content: Quote from: opampsmoker on November 15, 2020, 09:03:16 pmI am using 24VAC RMS rectified to approx 34VDC. I need higher input voltage.

author: Yansi
author_rank: Super Contributor
timestamp: November 16, 2020, 10:18:48 am
content: so then for a low current consumption application, use something like LM5007.Also, don't forget that there may be +-10% mains voltage variation and a small lightly-loaded transformer may add another +10% of voltage on top.So even 45V regulator won't cut the mustard, for a 24V rectified transformer supply. You need something 50V+ rated.Look for example athttps://www.monolithicpower.com/they make cheap good quality switchers.

author: ilium007
author_rank: Frequent Contributor
timestamp: November 16, 2020, 10:25:14 am
content: Quote from: Yansi on November 16, 2020, 10:18:48 amI am looking for something in the order of 1A - 1.5A

author: Yansi
author_rank: Super Contributor
timestamp: November 16, 2020, 10:35:02 am
content: That is not a low current then. Where did I read about low current? My bad then.Are you limited to using the "big brand names" or using the "standard" distributors? What quantity are we talking about?

author: ilium007
author_rank: Frequent Contributor
timestamp: November 16, 2020, 11:05:14 am
content: Quote from: Yansi on November 16, 2020, 10:35:02 amJust personal projects

author: Yansi
author_rank: Super Contributor
timestamp: November 16, 2020, 11:54:32 am
content: Then I'd suggest looking at lcsc.com, as there you can find tons of suitable modern switchmode regulators, both name brand ones and pure Chinese ones for what I cal "normal prices".Just open the switchmode category there, select 50V+ regulators and you'll find a LOT of available types beginning at about $0.5 a piece.https://lcsc.com/products/DC-DC-Converters_484.html

author: opampsmoker
author_rank: Regular Contributor
timestamp: November 17, 2020, 06:58:00 am
content: Quoteyou'll find plenty of similar chips to what i gave, but rated for your slightly higher voltage...and theres always LTM8063https://www.analog.com/en/products/ltm8063.html

author: poorchava
author_rank: Super Contributor
timestamp: November 17, 2020, 09:37:15 pm
content: Quote from: Unixon on November 08, 2020, 01:57:42 pmWell, that failure mode is true for any buck converter. They're is always a switch between input and output and if you blow it, it will fail short like 99.9% of the time since this is how mosfets fail up until in power ranges, where they just disintegrate explosively.I have abused those ST1S10s a lot and never had a single of them die in this way.

author: Unixon
author_rank: Frequent Contributor
timestamp: November 17, 2020, 11:27:30 pm
content: Quote from: poorchava on November 17, 2020, 09:37:15 pmIt would be nice to have them always short to ground and not to the output...What I learned from using this part is that ST1S10 wants perfect layout to work without special effects like instant package self-decapitation on power-up.I've been using different synchronous converters in different projects, but even higher frequency parts weren't that capricious.

author: Renate
author_rank: Super Contributor
timestamp: November 17, 2020, 11:49:18 pm
content: Quote from: poorchava on November 17, 2020, 09:37:15 pmWell, blowing up is one thing.Deciding to take a vacation and passing full voltage for a while then going back to your job and regulating is another thing.

author: dkonigs
author_rank: Regular Contributor
timestamp: November 18, 2020, 06:37:05 am
content: Quote from: bizkits on November 16, 2020, 08:59:46 amI've also used those RECOM DC-DC converters, and they work quite well. It does seem a little weird that the SMD version is actually more expensive than the thru-hole version, though. They also recently added a section on EMC filtering to the datasheet that wasn't there when I first used the part.

author: thinkfat
author_rank: Unknown
timestamp: November 18, 2020, 07:30:31 am
content: Quote from: Renate on November 17, 2020, 11:49:18 pmIf you care about this failure mode (don't know how common it is), then you will need some kind of independent protection circuit on the output, a crowbar circuit or beefy zener diode with a fast acting fuse.