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Topic: Step-down voltage supply (Read 1 time)previous topic - next topic

foxbat

Feb 11, 2011, 10:20 pm
I am supplying a regulated 3.3v to my circuit, however sub-circuits within my design require 2.5v and 1.8v. What do you think is the most efficient way to produce these levels from the 3.3v supply? Efficiency is a priority since this device will be battery powered.

RuggedCircuits

#1
Feb 11, 2011, 10:27 pm

If you drop 3.3V to 2.5V using an LDO, for example, it is going to dissipate (3.3-2.5)*Iload Watts of power. This means your efficiency is Pout/Pin=(2.5*Iload)/(3.3*Iload)=76%. Actually it's slightly worse due to the current consumption of the LDO itself. Meanwhile, switching regulators easily achieve >80% efficiency over most of their load current range.

Going from 2.5V to 1.8V your peak efficiency with an LDO is (1.8/2.5)=72% so again a switching regulator will have higher efficiency.

--
The Aussie Shield: breakout all 28 pins to quick-connect terminals

Grumpy_Mike

#2
Feb 11, 2011, 11:14 pm
It depends on what the circuits are but you are much better off generating the lower voltages from the same source as you got the 3v3. Again using switching regulators. If your 3v3 is not derived from a switching regulator then there is no need to worry about using switchers for the smaller sub systems as the extra gained is negligible in the whole sachem of things.

cmiyc

#3
Feb 12, 2011, 05:07 am
"most efficient way"?  Buck Converters:
http://en.wikipedia.org/wiki/Buck_converter
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

farope

#4
Feb 16, 2011, 09:34 am
I have similar requirements, although my initial voltage will either be 5 or 12 V. The required output voltages are 1.8 and 2.8 V. I had ordered a set of samples of LM22674 (http://www.national.com/ds/LM/LM22674.pdf) and LM22675 (http://www.national.com/ds/LM/LM22675.pdf) step down switches, but have realised that they are probably overkill for my project. As stated above, they're buck regulators, with ~ 90% efficiency with input voltage of 5 V (4.6 V min). Obviously, that's too high for your project, but I'm sure you can find equivalents.

As an aside, does anyone have any suggestions as to what the best way to step down 5 or 12 V to 1.8 and 2.8 V is? The switchers mentioned above are 500 mA and 1 A capable, and my project requires ~ 10 mA max. Thank you!

farope

#5
Feb 16, 2011, 10:26 am
I've answered my own question: this from TI (http://focus.ti.com/docs/prod/folders/print/tlv7101828.html) provides both 1.8 and 2.8 V outputs from a 5 V input.

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