_Cheap_ buck solution for 9-24V in  to 5V out, ~50mA to 1A - Page 1
Forum section: electronics / projects

author: Kremmen
author_rank: Super Contributor
timestamp: April 15, 2012, 02:23:05 pm
content: Hi all & greetings from Finland where the snow is finally gone and Miss Spring is in town.This is my first post to the forum so i am a noob here, although not otherwise.The topic really says it, but to fill in some details: I am in the process of designing a small instrumentation system mostly for CNC related stuff, based on Atmel processors and I2C bus. The idea is to distribute the system into measuring / data acquisition units, data processing units and display units. One unit may freely have multiple roles to minimize system cost. The idea is to create units as needed but using a common framework so existing units can be easily mixed and matched. Each individual unit is supposed to be small and low cost.This brings me to the point: Digikey and Mouser offer heaps of easily applied buck ICs that only need the inductor and a few random components to create a working PSU. This would be ideal only the price in small quantities is, well, disappointing. Paying 4 to 9 $ or € per chip is not in line with the rest of the stuff. A run of the mill ATMega328 for example goes for $ 3 and change. The target is to keep a typical unit definitely below 20 € (we are not competing with the Chinese here) but these chip prices already eat a quarter of that or worse.So, anyone been in the same situation came up with a brilliant solution?

author: mariush
author_rank: Super Contributor
timestamp: April 15, 2012, 02:51:50 pm
content: You must have really low filtering/searching skills.I bought these from Farnell :ON SEMICONDUCTOR - NCP3063BPG - V REG, SWITCH, BUCKBOOST, INV, 1.5Ahttp://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1369734It's less than 1$... 0.45 pounds... even cheaper in quantity.QuoteCheck the datasheet, it includes everything you need to know including schematics and pcb layout example.ps. and you'll find it's available from several manufacturers and in different packages, and all should have the same pinout, so you won't be stuck with a one manufacturer solution and possibily of having a hard time getting them :http://uk.farnell.com/jsp/search/browse.jsp?N=2031+203946&Ntk=gensearch&Ntt=3063&Ntx=mode+matchallpartial(there's actually two different chips in the search above, the second is with 33063 in name, which would work as well but has one different pin )

author: Kremmen
author_rank: Super Contributor
timestamp: April 15, 2012, 03:27:36 pm
content: Quote from: mariush on April 15, 2012, 02:51:50 pmOh, I must? Thanks for the quick eval. I'll have to write that into my resume.QuoteGood for you. I don't usually buy from Farnell so much but yes, that chip is available also from DK though not from Mouser. I was looking for higher switching frequency, closer to 1 MHz which i failed to mention in the first post, sorry for that omission. Also, while the specs look like it will work, i want to steer away from the QFN packages if at all possible. If this chip will do 1 amp only in that package i will have think about it.But yes, it is an answer to the question i asked. Thanks for replying.It would be even better to find a similar chip switching around 1 MHz to minimize the inductor size.P.S. Something like this:http://search.digikey.com/us/en/products/AP5100WG-7/AP5100WG-7DICT-ND/2277839. This is still over a buck (pun intended) in small quantities but better than 4 or 9 which was ridiculous.

author: TerminalJack505
author_rank: Super Contributor
timestamp: April 15, 2012, 03:34:17 pm
content: If you're wanting to keep cost at a minimum and not necessarily space at a minimum then the lower frequency switchers are probably the way to go. In addition to the cost of the IC, you need to consider the cost of the capacitors. Some of the higher frequency switchers require crazy-largeceramiccapacitors (22uF!?) Which don't come cheap.

author: Kremmen
author_rank: Super Contributor
timestamp: April 15, 2012, 03:43:07 pm
content: Point taken but at least i have had good luck paralleling 10 uF caps which are readily available at least below 25 V rating.This exercise is far from completed so everything can be adjusted. Just now my priority seems to be minimizing the inductor size to avoid cumbersome boulders on the tiny PCB, possibly even causing grief during the reflow process (these will be mostly assembled with hobbyist level competence). But even that point is still open to discussion.Edit: I did a quick naive calculation comparing the prices from DK for 1-10 units. While not scientifically accurate, it shows that the higher frequency solution would be some $ .3 more expensive if using the recommended single 22 uF ceramic output cap. Replacing that with 2 x 10uF caps reduces the price to just under the lower freq solution. The larger inductor is quite a lot more expensive than the small one, as i suspected.Based on this i opt for the higher freq solution if only to conserve PCB area and minimize the component mass.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 15, 2012, 06:53:53 pm
content: The cheaper buck chips tend to be more obscure - a few I've used in the past for 24v input to 3.3 or 5V are A4447 (Allegro), SC4524A (Semtech - note the A for 24V), FAN8303 (fairchild). All are pretty similar, and cheap but not always in stock.I think Microchip has brought something out pretty recently, so may be worth a look.

author: Zero999
author_rank: Super Contributor
timestamp: April 15, 2012, 11:57:28 pm
content: If you want cheap, you can make a simple SMPS with a couple of transistors:http://www.romanblack.com/smps/smps.htm

author: Psi
author_rank: Super Contributor
timestamp: April 16, 2012, 12:13:33 am
content: What about this. Module with everything built inhttp://www.digikey.fi/scripts/dksearch/dksus.dll?vendor=0&keywords=945-1648-5-ND3.06 Euro in qty 1 and you don't have to buy any extra components.- 570 KHz Switchmode module- Efficiency up to 92 %- Short Circuit Protection- Pin Compatible with 78 Series Regulators- 5V / 500 mA Output- 7 - 28V DC input

author: Kremmen
author_rank: Super Contributor
timestamp: April 16, 2012, 04:39:56 am
content: Quote from: Psi on April 16, 2012, 12:13:33 amNow that is interesting. I did search for hybrids but not very thoroughly so i missed this. While it does only 500 mA instead of the full amp, it could be a candidate.Meanwhile I came up with this. It uses a Diodes AP5100 and will do 1,5 A for something like $ 2 or just over. The board dimensions are 14 x 14 mm.Done in Diptrace by the way. I like that tool a lot despite its messy library system which i hope they will fix one day. There is no 3D model for the Taiyo Yuden inductor so you see only the pads. This is just a first draft anyway, I am not sure if I actually want to have an aluminium cap for input filtering.Could be I opt for Psi:s module instead. The price difference is not that big and it would save a lot of effort + ensure that the thing actually works which is always nice.

author: Kremmen
author_rank: Super Contributor
timestamp: April 16, 2012, 04:51:27 am
content: Quote from: mikeselectricstuff on April 15, 2012, 06:53:53 pmThanks for this as well. I have had good luck with Fairchild FAN series in the past. In one specific case i managed to repair a number of Yaskawa Sigma II series servo drivers by implementing a replacement hybrid PSU for the internal power using a FAN7554. Saved me some 2000 € in repair costs. So i have warm feelings towards the FANs

author: Psi
author_rank: Super Contributor
timestamp: April 16, 2012, 05:24:36 am
content: Quote from: Kremmen on April 16, 2012, 04:39:56 amThey do have a 1A version, but it's over 7 euro

author: Kremmen
author_rank: Super Contributor
timestamp: April 16, 2012, 08:36:03 am
content: Well, could still be the way to go despite the high price of the 1 A part. Not every module will need the full 1 amp and since the parts are interchangeable, it would be dead easy to pick the one with enough kick to do the job.Again, big thanks for an immediately workable and above all easy solution.