Cooler LDO? - Page 1
Forum section: electronics / beginners

author: LEDAero
author_rank: Regular Contributor
timestamp: August 07, 2015, 12:48:18 pm
content: Hi,I need to get a 3.3V power source from my 12.9V supply. I run 12V motors but my digital components are 3.3V.Currently I am using an SMD 1117-33 LDO, but it gets pretty darned hot, regardless of load. To make matters worse, the circuit is designed to be used on a boat, so will be encased in poly or epoxy or similar. I am concerned that the heat will just build and build and eventually the LDO will burn out - or start a fire!Is there a better, cooler way of transforming down to 3.3V from 12V? I have plenty of space available on my PCB to mount stuff - this version of my design is using sub-assemblies, so there is lots of bare real estate.I did think about a through-hole 1117 with a small heat-sink, but that will make packaging a bit problematic. Of course I could drill a hole and use the ground plane as a heatsink.But... I'm a bit of a novice and this and don't know where to go.My Dad suggested a couple of 1117's in parallel?

author: wraper
author_rank: Unknown
timestamp: August 07, 2015, 01:08:47 pm
content: The heat amount won't change regardless how many of them you will connect in parallel (and that's not a good idea BTW, you can't just connect the outputs together). If you crank the same amount of heat dissipation on the same board space (unless they are big distance away from each other) while using copper pour as the heatsink, the result won't be too much better. If you really want less heat, then use buck converter.

author: LEDAero
author_rank: Regular Contributor
timestamp: August 07, 2015, 01:12:50 pm
content: Quote from: wraper on August 07, 2015, 01:08:47 pmA buck converter being a transistor, an inductor and a diode, correct?Could you give me an idea of the kind of components I would need to handle up to 1A of current?And thanks for the answer - I especially appreciate the info about the heat. I suspected that the 1117 was going to run pretty warm - it is only drawing 170mA, out of a potential 800mA and it's already too hot to comfortably touch.

author: LEDAero
author_rank: Regular Contributor
timestamp: August 07, 2015, 01:17:09 pm
content: oh... while I was googling I found this on buck-converter design.QuoteNoise may be a consideration - we have a GPS and 9DoF compass/accelerometer in reasonable proximity.I suppose the level of noise is all relative and I should just 'suck it and see', as they say back home

author: Miles Teg
author_rank: Regular Contributor
timestamp: August 07, 2015, 01:20:05 pm
content: Yes, rules on LDO is it will dissipate the gate of voltage multiplied bu current. So 170mAx 8.7 ~ 1.7WFast way to get a choice on a buck converter would be to put your requirement on ti webench:http://webench.ti.com/webench5/power/webench5.cgi?lang_chosen=en_US&VinMin=10&VinMax=14&O1V=3.3&O1I=1&op_TA=30Like i see the TPS62177 is a reasonable choice with relatively few components.Oups, not for 1amp...Webench will show you list of advised components to put around.

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: August 07, 2015, 01:20:35 pm
content: You can get one of these cheap chinese ebay modules, but be conservative on the specifications .http://www.ebay.com/itm/DC-to-DC-Buck-Converter-Power-Module-1-25V-36V-5A-Step-Down-Breadboard-/251959445554?pt=LH_DefaultDomain_0&hash=item3aa9f40832

author: LEDAero
author_rank: Regular Contributor
timestamp: August 07, 2015, 01:21:58 pm
content: You misunderstand... I don't want a module - any mug can buy from a catalogue. I want to integrate 3.3V regulation into my PCB.I thought that was clear in my posts above?

author: LEDAero
author_rank: Regular Contributor
timestamp: August 07, 2015, 01:22:42 pm
content: Quote from: Miles Teg on August 07, 2015, 01:20:05 pmThanks Miles - that is extremely helpful

author: wraper
author_rank: Unknown
timestamp: August 07, 2015, 01:25:18 pm
content: Quote from: LEDAero on August 07, 2015, 01:12:50 pm12-3.3 = 8.7 V of voltage drop which multiplied by 0.17 W results in 1.5 W of power dissipated. Quiet a lot for a part which uses PCB as the only heatsink. Generally buck (step down) converter of such power is based on some IC, inductor, diode, capacitors and a few additional components. If you aren't sure about being able to design it into the PCB, you can buy some readily available modules.http://www.ecircuitcenter.com/Circuits/smps_buck/smps_buck.htm

author: jdraughn
author_rank: Regular Contributor
timestamp: August 07, 2015, 01:26:06 pm
content: These are $1.55 with free shipping, Just expect to wait a looong time to get them, but only 3.00 from the US warehouse, probably get it in less then a week then.Input voltage: 4.5V ~ 28VOutput voltage: 0.8V ~ 20VOutput current: rated current is 2A, maximum 3A (Additional heatsink is required)Conversion efficiency: 96% (Highest)Output ripple: < 30mVSwitching frequency: 1.5MHz (Highest) 1MHz (typically)Work temperature: -45°C to +85°Chttp://www.banggood.com/Mini-DC-DC-Converter-Step-Down-Module-Adjustable-Power-Supply-p-920327.html

author: Miles Teg
author_rank: Regular Contributor
timestamp: August 07, 2015, 01:27:27 pm
content: Quote from: LEDAero on August 07, 2015, 01:22:42 pmTake care of the first results I show you. I made a search as I thought your requirements were 0.2A only.You can modify easily the calculator input to get a 1A solution.

author: PSR B1257
author_rank: Frequent Contributor
timestamp: August 07, 2015, 01:27:54 pm
content: Something likehttp://www.digikey.com/product-detail/en/R-783.3-1.0/945-1036-ND/2256216is even pin compatible to a linear voltage regulator.

author: LEDAero
author_rank: Regular Contributor
timestamp: August 07, 2015, 02:15:39 pm
content: Quote from: Miles Teg on August 07, 2015, 01:27:27 pmI caught that early on. Thanks though - it got me started at a skip, rather than a plod

author: LEDAero
author_rank: Regular Contributor
timestamp: August 07, 2015, 02:17:24 pm
content: Quote from: PSR B1257 on August 07, 2015, 01:27:54 pmDamn... I actually have some of those in my toolbox in 5v - never thought of them. But they are expensive... $7.50 would make it the most expensive component we will be using - more expensive than the Arduino DUE that powers the whole thing(we buy them for $6.10).

author: LEDAero
author_rank: Regular Contributor
timestamp: August 07, 2015, 02:19:08 pm
content: Quote from: jdraughn on August 07, 2015, 01:26:06 pmI'm in SE Asia, not in the US and that doesn't help me design a regulator for SMD'ing on a PCB of my own design - but thanks anyway.

author: LEDAero
author_rank: Regular Contributor
timestamp: August 07, 2015, 02:23:39 pm
content: Quote from: wraper on August 07, 2015, 01:25:18 pmThanks wraper - between the ecircuitcenter page and the Webench tool, I think I could manage itThanks again to you and Miles and PSR - you have been extremely helpful. I thought I would be chasing this around for a week or so before I got a result - EEVblog is great for us n00bs!Cheers