Modern switcher? - Page 1
Forum section: electronics / projects

author: miceuz
author_rank: Frequent Contributor
timestamp: April 24, 2015, 06:44:27 am
content: I need to make a switching DC to DC converter that will be powering Rasberry Pi and some WS2812 leds. Input voltage - 12VDC, output - 5V @ 2A max. Ripple is not hugely important, probably would be nice to keep below 0.1Vp-p. Efficiency is not hugely important too, I just want to keep the power dissipation to the minimum. The system will be using ~400mA constantly.Can someone recommend me a modern switching regulator for the task? There is a huge selection of them, I'm at loss. I'm also considering using MC34063 with an external transistor, but I'm not sure, I have never designed a switcher before. Please help

author: rx8pilot
author_rank: Super Contributor
timestamp: April 24, 2015, 06:56:03 am
content: One off?Target package?Hand Soldering?Cost sensitive?Isolated?integrated or controller?I have been using TI's TPS53915 and it has been working quite well. i2c/SMBUS for monitoring and trimming. .4mm QFN package is not for beginners. Up to 1 Mhz Fs so you can use tiny inductors if efficiency is not critical. Output caps are ceramics so the overall size is very small. I use 7x 10uf 0805 caps. Overkill for your application at 12A, but is is efficient and robust. No heat sink needed.

author: miceuz
author_rank: Frequent Contributor
timestamp: April 24, 2015, 07:58:03 am
content: Quote from: rx8pilot on April 24, 2015, 06:56:03 amWe will be manufacturing in hundreds, so no, not one-off, but not super mass production. Hand soldering using paste stencil and oven is a must for now. Non-isolated. Cost - wise I want to end up not much more expensive than LM7805 with a huge heatsink they are using now (1.46€ total)I'm looking at TPS54339 now..

author: SteveyG
author_rank: Unknown
timestamp: April 24, 2015, 08:52:44 am
content: What's driving your need for 12V input? Automotive use?

author: miceuz
author_rank: Frequent Contributor
timestamp: April 24, 2015, 09:41:20 am
content: Quote from: SteveyG on April 24, 2015, 08:52:44 amNo, not automotive use. The most power hungry component in the system is 5 meters of 12V LED strip, that's why we have a pretty beefy 12V power supply.

author: langwadt
author_rank: Super Contributor
timestamp: April 24, 2015, 10:01:32 am
content: Quote from: miceuz on April 24, 2015, 07:58:03 amlots of tiny boards with mp1584 on ebay at less than that pricehttp://www.ebay.co.uk/itm/291146781922you can build you own, though it might be hard to beat the price

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 24, 2015, 02:53:23 pm
content: TPS54xxx are usually good, an LM26xx SimpleSwitcher would also do. Both are pretty small on components, and perform well. Follow the appnotes for parts selection (they probably have a standard 5V 2A design all ready to go for you..) and layout and you should be fine.If you want to design/build boards, you might as well buy the dev kits instead. If you're going to dead-bug them, do use a ground plane method.Tim

author: tonyarkles
author_rank: Regular Contributor
timestamp: April 26, 2015, 09:34:04 pm
content: I'm more than happy to admit that I'm pretty lazy when it comes to power supply design and love to use TI WEBENCH. I've built a few supplies using it and have never had a problem.I punched in Vin_min = 11V, Vin_max = 15V, Vout = 5V, Iout_max = 2A and got this design:http://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=1A09CC4364A3A0D0Gives a BOM cost of $1.14 usd for 1k units.

author: rx8pilot
author_rank: Super Contributor
timestamp: April 27, 2015, 03:56:38 pm
content: TI's Webbench is a good tool to rough in a power supply, but it does not help much with PCB layout or other elements that are non-ideal. When I started learning about power supplies about 18 months ago, I learned that slapping a schematic on a PCB gives a predictably low performance result.It took many, many hours of study to get a high performance design worked out.

author: tonyarkles
author_rank: Regular Contributor
timestamp: April 29, 2015, 01:56:02 pm
content: Quote from: rx8pilot on April 27, 2015, 03:56:38 pmAbsolutely. The best part about WEBench is that it helps pick out appropriate parts, because... there's so damned many of them and I don't really want to become an expert in all of them. WEBench gives me a nice list of different designs, I'll pick the one that best meets the requirements and then pull down the datasheet and learn as much as possible about it.