Efficient 3.3v/5v rails from 7v-12v - Page 1
Forum section: electronics / beginners

author: ziplock9000
author_rank: Regular Contributor
timestamp: September 27, 2018, 05:36:57 am
content: I currently have a project the uses 3.3v and 5v rails of up to ~300mA of average power use each. They are fed by a design which uses two AMS1117 linear regulators that are provided anything from 7v to 12v depending on the power supply I'm using. Sometimes a wall wart, sometimes a bunch of 18650's.. It depends as I'm still in the prototyping stage of the power supply.This solution as you can imagine is not very efficient, lots of power is lost as heat via the linear regulators.So to fix this I was thinking of using a synchronous buck converter to take the 7v-12v down to 5v.. Then after that I'm not so clear what to do for the 3.3v rail..Should I use another sbuck to take 7-12v down to 3.3v? or one to take 5v down to 3.3v or just use an AMS1117 to take 5v to 3.3v? Maybe there's a module or IC that does both voltages in a very efficient manner?I can imagine this question has been asked a million times, but my Google fu found nothing definitive.I need this to be as efficient as possible because eventually I'd like to run this from batteries.. So what's the best solution that is still cheap?

author: palpurul
author_rank: Regular Contributor
timestamp: September 27, 2018, 05:50:14 am
content: The first thing that comes to my mind is multiple output buck converters.Here is a list from Analog devices website:ListThis ICseems suitable.It's got two outputs with enough current capability and It doesn't even been diode.

author: ziplock9000
author_rank: Regular Contributor
timestamp: September 27, 2018, 05:53:58 am
content: Brilliant thanks. I was hoping such a thing existed as obviously it's needed.Now if I can get a Chineasum complete module with all of the support components that does this then I'm laughing.

author: palpurul
author_rank: Regular Contributor
timestamp: September 27, 2018, 05:56:55 am
content: Quote from: ziplock9000 on September 27, 2018, 05:53:58 amCheck out the other manufacturers they might have cheap (probably not that cheap) evaluation module for that kind of chips.

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 27, 2018, 06:06:44 am
content: As an FYI even if you want to keep it simple you're under no obligation to go to the Chinese on this. Example:https://www.digikey.com/product-detail/en/texas-instruments/LMZ21700SILR/296-44325-1-ND/6110599

author: ziplock9000
author_rank: Regular Contributor
timestamp: September 27, 2018, 06:35:48 am
content: Interesting, about 90% efficient when Vout = 5v @ load=300mA.I wonder if there's any of these dual packages closer to 95%/96% efficient like the MPQ4460/LMZ21700/MP2315 are for single rails and still at a good price and as easy to use as possible... I know... and the kitchen sink

author: ziplock9000
author_rank: Regular Contributor
timestamp: September 27, 2018, 06:52:06 am
content: I've found this Chinesium dual buck module that claims to be 93% efficient, although who knows as they have scraped the chip number offhttps://www.aliexpress.com/item/30W-DC-DC-Step-Down-Dual-Power-Supply-Module-Adjustable-Voltage-Conversion-Board/32869342182.html£6.51 GBP delivered to the UK.It's also dual in that it's +ve and -ve, not two positive's.. so no good :/

author: xani
author_rank: Frequent Contributor
timestamp: September 28, 2018, 02:28:26 pm
content: Quote from: ziplock9000 on September 27, 2018, 06:52:06 amIf you set negative voltage to 3.3 and positive voltage to 1.7V you will get what you want.| -3.3V | 0 | +1.7V | is same as | 0V | 3.3V | 5V | , with a caveat that you can't connect input "0V" to output "0V". I'd personally just buy 2 single ended modules if I couldn't find double-ended one

author: ziplock9000
author_rank: Regular Contributor
timestamp: September 28, 2018, 04:42:29 pm
content: I've been able to find some well priced 5v ones based on the MP1584EN and MP2315 ( better), but no 3.3v as of yet.