Small voltage regulator - Page 1
Forum section: electronics / projects

author: JJalling
author_rank: Unknown
timestamp: September 06, 2013, 08:47:33 am
content: Hi,i'm in the process of designing a decoder for model railroad. The design is constrained to about 14x14mm.It contains a uC, some leds and some other descrete components.Some specifications:Input voltage: 12-20VOutput voltage: 3.3-5VMax output current: 30-40mACan you guyes recommend a small power supply solution? My first thought was a small ua78l05, but i don't want the thing to get too hot.BR Jonas

author: M. András
author_rank: Super Contributor
timestamp: September 06, 2013, 08:54:20 am
content: look for surface mount swtiching regulators which is everything in it

author: fcb
author_rank: Super Contributor
timestamp: September 06, 2013, 09:36:19 am
content: MC34063 is my cheap 'goto' SMPS regulator.

author: JJalling
author_rank: Unknown
timestamp: September 06, 2013, 09:44:40 am
content: Inductors are big :-(Well, it seems like its the way to go. Thanks guys.BR Jonas

author: alxnik
author_rank: Regular Contributor
timestamp: September 06, 2013, 10:25:54 am
content: Even for such a big voltage drop, 40mA are not much, about 0.6W dissipation max. Find a regulator with a big ground pad and solder it on the ground plane, you should be able to get away with it

author: M. András
author_rank: Super Contributor
timestamp: September 06, 2013, 12:56:37 pm
content: nah the he mentioned the whole project size is 14x14mm a to220 is much larger than that

author: Marco
author_rank: Super Contributor
timestamp: September 06, 2013, 01:18:00 pm
content: What's your height budget? Can something like this fit?http://www.adafruit.com/products/1065#Downloads

author: mariush
author_rank: Super Contributor
timestamp: September 06, 2013, 01:32:26 pm
content: Have a look at chips like AP1509 , LM257* , LM2672, MIC4680 etc .. most of these are high frequency switchers, so they only need a surface mount diode and inductor, and a couple of ceramic capacitors. Maybe a couple of resistors if you get adjustable versions of these...examples :ap15093.3vhttp://uk.farnell.com/diodes-inc/ap1509-33sg-13/ic-buck-reg-3-3v-2a-8sop/dp/18253225vhttp://uk.farnell.com/diodes-inc/ap1509-50sg-13/ic-buck-reg-5v-2a-8sop/dp/1825323adjhttp://uk.farnell.com/diodes-inc/ap1509-sg-13/ic-buck-reg-2a-8sop/dp/1825324lm25743.3vhttp://uk.farnell.com/texas-instruments/lm2574n-3-3/switching-reg-0-5a-3-3v-2574-dip8/dp/94935305vhttp://uk.farnell.com/micrel-semiconductor/lm2574-5-0yn/buck-40vin-52khz-0-5a-5v-8dip/dp/2100264adjhttp://uk.farnell.com/texas-instruments/lm2574hvn-adj/ic-switching-reg-adj-2574-dip8/dp/9489932lm26723.3/5/adjhttp://uk.farnell.com/texas-instruments/lm2672m-3-3/switching-reg-1a-3-3v-2672-soic8/dp/4466550http://uk.farnell.com/texas-instruments/lm2672m-5-0/switching-reg-1a-5-0v-2672-soic8/dp/9489797http://uk.farnell.com/texas-instruments/lm2672m-adj/switching-reg-1a-adj-2672-soic8/dp/9489789mic46803.3/5/adjhttp://uk.farnell.com/micrel-semiconductor/mic4680-3-3ym/buck-4-34vin-1-3a-200khz-3-3v-8soic/dp/2219078http://uk.farnell.com/micrel-semiconductor/mic4680-5-0ym/ic-buck-reg-1a-5-0v/dp/1556735http://uk.farnell.com/micrel-semiconductor/mic4680ym/reg-step-down-1a-200khz-smd-4680/dp/1100657See datasheets on those pages ... note that most of the above are available in SOIC, DIP8, to263 etc so in small packages. Search for the IC name on the site or other sites like digikey/mouser/newark/rs-components and you'll find it in other packages.

author: ben7
author_rank: Contributor
timestamp: September 07, 2013, 06:42:52 pm
content: I think the LMR14206 will be good for your project. Tiny SOT-23-6 package. 600mA output current maximum. 42V input voltage maximum. It runs at 1.25MHz. With frequencies this high, you only need a tiny smd inductor and tiny smd MLCC capacitors!It will really save space.You need a higher frequency regulator because the inductor and capacitor(s) will be smaller, and hence they will save a ton of space. And you won't need a giant heatsink plane, if you will even need one!P.S. I do model railroading too! Be sure to incorporate a way to eliminate any noise/spikes from the voltage input to the decoder, such as from dirty wheels and tracks, or else you might get random resets, or possibly self destruction! Same goes for the motor driver h-bridge. Be sure to pick the best MOSFETs or transistors for the motor driver, as the decoder is so small, heat can't be dissipated very well.

author: Monkeh
author_rank: Super Contributor
timestamp: September 07, 2013, 06:53:30 pm
content: Look at the LM2937/LM2940IMP for a small (SOT-223) LDO. Just be careful about dissipation.

author: JJalling
author_rank: Unknown
timestamp: September 09, 2013, 09:50:21 am
content: Hi everybody,thanks for all your suggestions. I think I will give the ua78l05 a try, and if heat is a problem, look at a high frequency switcher.BR Jonas