3V to 3.3V using D Cell Batteries Best Approach - Page 1
Forum section: electronics / beginners

author: Veramacor
author_rank: Regular Contributor
timestamp: August 28, 2013, 02:15:43 pm
content: I have a project that needs to run remotely and at times I need about 300 millamps for short periods. Most of the time the project will run about 300 microamps.I want to get the best battery life out of 2 standard D cell batteries, and my project has a need to run at 3.3VAny suggestions on a step up regulator with an ultra low quiescent current? I'm looking at about 700 microamp average current draw and would like to get about 2 years or so out of my batteries.Thanks!

author: AndyC_772
author_rank: Super Contributor
timestamp: August 28, 2013, 02:46:14 pm
content: It's not a trivial problem. Can you not use 3x C cells instead of 2x D cells, then use an ultra-low quiescent current linear regulator to drop the voltage down to 3.3V?Failing that, I'd be looking long and hard at ways to make the circuit operate at a lower voltage. What is it that specifically requires 3.3V? Can the circuit not be modified to run at, say, 2.5V instead?

author: grumpydoc
author_rank: Super Contributor
timestamp: August 28, 2013, 02:50:43 pm
content: QuoteI'd have thought most "3.3V" logic would run at 3V2xD cell would be 3.2-3.3V fresh and lightly loaded anyway.QuoteShould be OK - if you have 12,000mAh alkaline D cells they will last 714 days (in theory).Edit: Actually, thishttp://www.ti.com/lit/ds/symlink/tps61006.pdfmight do you. 44µA quiescent and 80-90% efficient. Also something like a Duracell Ultra will probably give you 16-18,000mAh when lightly loaded so you should get your two years (just).Nothing special about the above - just the first boost converter IC in Farnell's list designed for 3.3V output

author: mariush
author_rank: Super Contributor
timestamp: August 28, 2013, 05:11:35 pm
content: Have a look at LT1308:http://www.linear.com/product/LT1308It has higher quiescent current at about 100 uA but it has a shutdown pin which takes it down to about 3 uA so if your IC uses so little power for long times it might be possible to do some tricks like charging a small capacitor/supercapacitor then running for minutes with the boost converter shut down and so on.

author: Veramacor
author_rank: Regular Contributor
timestamp: August 28, 2013, 09:40:36 pm
content: Wouldn't one advantage of a boost converter instead of a step-down regulator be that I could get 3.3V with drained batteries going as low as .7V (depending on boost converter)It would seem that I could get more then 12,000 milliamp hours if that was the case assuming that 12,000 ma/h is for a D cell maintaining 1.5v.I agree I wouldn't get much more, but I think I've seen a boost converter provide 200 milliamps at 3.3v with as low as a .7V input...

author: Veramacor
author_rank: Regular Contributor
timestamp: August 28, 2013, 09:52:54 pm
content: Quote from: AndyC_772 on August 28, 2013, 02:46:14 pmThe bottleneck in the project is a wifi module. The ratings say absolute minimum voltage is 3.1V, but designed for 3.3V. My PIC mcu can go down to 1.8V. I could look into turning the WIFI off, but it's sleep mode is 5 microamps, meaning I can keep it 'on' for little current cost. Turning it on may be troublesome, but that is a possibility, Just running the micro at 1.8V and using a boost regulator to turn on and utilize 3.3v. Very complex setup though

author: lgbeno
author_rank: Frequent Contributor
timestamp: August 28, 2013, 10:57:03 pm
content: Check out TI TPS61200 very low Iq.It's a boost converter that also has the capability to do down conversion so you can run your wifi module through the entire voltage range of 2 alkalines.You may want to consider running you pic right off battery anyway to make the system more effiecnt then put the regulator to sleep when wifi is not on.Just be careful because you cannot alway run the micro at max freq when using low voltage vin.Tps61200 is a pretty neat part...

author: Veramacor
author_rank: Regular Contributor
timestamp: August 29, 2013, 01:02:47 pm
content: Quote from: lgbeno on August 28, 2013, 10:57:03 pmThanks for the info. I will check it out. Sounds promising - thanks!