[SOLVED] Low Cost 12v to 5v DC to DC switching reg alternatives to LM7805 - Page 1
Forum section: electronics / beginners

author: castingflame
author_rank: Regular Contributor
timestamp: October 14, 2019, 08:31:36 am
content: I have a requirement for some 12VDC to 5VDC switching (buck) converters to replace the ubiquitous fixed linear LM7805 regulator.I currently use the Traco TSR1-2450 and there are similar modules available from Murata and Recom. They are perfect for what I need but the downside is cost. They normally come out at around £6 to £12 delivered. I am looking for something closer to £2-£3 delivered.RequirementsPin compatible drop in replacement for the linear 78 series regulators.£2-£3 delivered.Existing module or homebrew tiny footprint pcb is okay if similar to 7805/Traco footprint.800mA min up to 2Amp max.For more detailed spec requirements look at the Traco TSR1-2450.I am happy to buy an existing module like the above or alternatives. Additionally,I am happy to create a tiny PCB with SMD components and make the units myself if need be.I don't want to get into the dark art realms of switching designs, so any new design will need to be based on existing schematics.Thanks

author: Gyro
author_rank: Super Contributor
timestamp: October 14, 2019, 09:21:40 am
content: Sorry to say that you're always going to be onto a cost loser trying to fit a pin-compatible switching regulator drop-in for a linear part. The onlycompletelycost-effective way is to modify your board design to include the revised regulator circuit on board.I understand your nervousness about getting into a switching design but this is a pretty much jellybean application these days, a switching chip, inductor, rectifier and a few caps. A lot more compact if your existing board is smd. All switchmode IC datasheets will include a sample circuit, and many, an example layout too, though the pinout usually makes this self evident.Your though about building your own tiny smd board is the second best solution. You can prototype it with minimal risk to your product. This ebay listing shows the minimal level of complexity..https://www.ebay.co.uk/itm/1X-MURATA-POWER-SOLUTIONS-7805SR-C-IC-SWITCHING-REGULATOR/392356245046?hash=item5b5a412e36:g:sP8AAOSwtV1dOjvW(that is a high quality one by the way). It still won't be as cheap overall as integrating it into your main board due to cost of header, separate PCB, additional assembly etc, but that really depends on your volume.You can probably easily meet your £2-3 goal if you purchase less tightly specified PCB modules from China but I wouldn't really recommend that path.P.S.Ignore the details of that ebay listing - it's from one of those unscrupulous ebay sellers who re-list RS and Farnell parts at twice the price, it was simply an easy-to-hand photo to demonstrate the board complexity. That one has a lot of capacitance on board, whether you need that much really depends on the noise sensitivity of a circuit originally expecting a linear regulator - hard to comment without knowing more details of your board / product.

author: Zero999
author_rank: Super Contributor
timestamp: October 14, 2019, 09:49:17 am
content: There was a thread a couple of days ago about a Chinese DC:DC converter module, which appears to be suitable for replacing the LM7805, at a lower cost, especially given that no heatsink is required. I haven't tried it, but don't expect 3A of output current, keep it to 1.5A maximum.https://www.eevblog.com/forum/chat/has-anyone-tried-this-buck-converter-board-42-cents-each/https://www.aliexpress.com/item/32884011122.html

author: voltsandjolts
author_rank: Unknown
timestamp: October 14, 2019, 11:24:39 am
content: Quote from: castingflame on October 14, 2019, 08:31:36 am2.60+VAT at quantity 1https://uk.farnell.com/2760747

author: mariush
author_rank: Super Contributor
timestamp: October 14, 2019, 11:27:51 am
content: Make your own, using dc-dc regulator ICs likeAOZ6662 (35 cents each if you get 25):https://www.digikey.com/product-detail/en/alpha-omega-semiconductor-inc/AOZ6662DI-01/785-1858-1-ND/10258157AP65111:https://www.digikey.com/product-detail/en/diodes-incorporated/AP65111AWU-7/AP65111AWU-7DICT-ND/7652826AP65211:https://www.digikey.com/product-detail/en/diodes-incorporated/AP65211AWU-7/AP65211AWU-7DICT-ND/7652825examples of fixed voltage regulators:AP1509 :https://www.digikey.com/product-detail/en/diodes-incorporated/AP1509-50SG-13/AP1509-50SGDIDKR-ND/1301964AP63205 :https://www.digikey.com/product-detail/en/diodes-incorporated/AP63205WU-7/AP63205WU-7DIDKR-ND/9858432Add an inductor that's 50 cents or less, a diode, a couple ceramic resistors and capacitorsPCBs can be ordered at jlpcb for 2$ for 5-10pcs, or you could probably order a big panel with 50-100 to-220 sized circuit boards for something like 10-20$With the first regulator, it's running at high enough frequency that you'd be able to use smaller ceramic inductors and capacitors, so basically you could make your whole board surface mount and put solder paste on pads then components on top of pads and heat the tiny circuit board with a hot air gun or even go as far as to heat it on a metal plate on the kitchen stove

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 14, 2019, 12:15:35 pm
content: TI'swebenchsuggests some really nice circuits using TPS53318/TPS53319 with just one inductor, and a handful of resistors and capacitors, with something like 92-95% efficiency (over the 10-22V input range), at up to several amps of output current:It's an LSON-CLIP-22 package, which is probably tricky to solder (needs a hot air gun or oven), but the parts are available at LCSC and almost within the price range OP mentioned -- it's just one 2.2µH inductor, nine caps, and nine resistors, and the TPS53318/9 chip --, but because I'm just a hobbyist with no practical experience in switchmode supplies, I have no idea whether this design would work well or not. I'd love to know, though. An example board design in EasyEda would be awesome... especially if adding optional optoisolated enable signal input.

author: mariush
author_rank: Super Contributor
timestamp: October 14, 2019, 03:49:07 pm
content: How is that circuit easier than the ones used by the chips I suggested above?The datasheets are full of instructions and examples and the chips themselves are much simpler than "everything but the kitchen sink" of those TPS chips. He doesn't need power good and TRIP pins and other features, he wants a dumb 7805 replacement.

author: rsjsouza
author_rank: Super Contributor
timestamp: October 14, 2019, 05:00:18 pm
content: LM2596? It can be done with a very low component count.http://www.ti.com/product/LM2596

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 14, 2019, 06:23:22 pm
content: Quote from: mariush on October 14, 2019, 03:49:07 pmIt is not. It is a circuit I've wondered about for some time now, as an option for powering 5V single board computers, at several amp currents.I did not intend to imply it was better than the previous recommendations; I just wanted to add something to consider.Quote from: mariush on October 14, 2019, 03:49:07 pmPerhaps, but I don't do "shut up and answer the question"; I always explore the context. The additional viewpoints tend to provide value, even though now and then they are complete misses. Statistically, thus far it has been worth it.The same circuit as the one I showed (with different resistor, capacitor, and sometimes inductor value) keeps popping up in my webench experiments, trying to find an efficient hobbyist-DIY-able DC-DC converter to 5V and 3.3V. But, I can't seem to find existing projects or schematics using those chips. Aside from the chip itself being a bit scary to solder (by someone not familiar with hot air soldering, and who does not have an oven for soldering), the circuit looksinteresting, and I'd like to know more. Just by soldering one together, without having any way to measure EMI and such, or detect any gotchas known to those experienced with such circuits, I wouldn't learn much by myself.

author: castingflame
author_rank: Regular Contributor
timestamp: October 18, 2019, 08:03:52 am
content: Thank you everybody.This has given me plenty to think about. I am going to try a few of the suggestions.1. The Aliexpresshttps://www.aliexpress.com/item/32884011122.html(maybe to use as is or move the components to a more basic design PCB with better capacitor etc). Will work out very cheap so will order some to test and destroy.2. LM2596 can also be purchased cheaper as a module from china so similar to above.3. The Recom R-78E5.0-1.0 may be a little too close and not leave enough headroom so I will try and tie down the requirements a little better and look at this too.4. Look at some of the suggestions frommariushthat was kindly suggested. The price on some of these look favourable too.Thank you again, I feel like I have some viable options to test now. FWIW the application is not for a new design, rather to replace the LM7805 in an existing PCB.

author: mikerj
author_rank: Super Contributor
timestamp: October 18, 2019, 09:57:18 am
content: Quote from: castingflame on October 18, 2019, 08:03:52 amA device marked as LM2596 on a module can be purchased cheaper than the genuine part from TI...

author: mariush
author_rank: Super Contributor
timestamp: October 18, 2019, 11:30:56 am
content: Keep in mind that the LM2596 modules from eBay may be made with LM2576 chips (they erase the text and re-print the chips with the LM2596 text) ... the difference is lower switching frequency (around 52kHz for LM2576)Also, the chip may actually be a XL3000 something clone of LM25x6 chips.Basically, be wary of those cheap modules.