Go Down

Topic: Good 3,3 Volt power source (Read 1 time) previous topic - next topic

Zealot

With devices like the ESP8266 becoming more and more popular, a good 3,3 Volt power source becomes really important. imho.

Is it possible to avoid, or at least minimize the negative effects (power dissipation), of LDOs? Which batteries would be advisable?

Wawa

#1
Apr 16, 2015, 12:26 pm Last Edit: Apr 16, 2015, 12:26 pm by Wawa
Small buck regulators can be very efficient, have very low dropout, and very low idle current.
Like this one.
Leo..

RogerRowland

As an alternative to the buck, you could try a smaller battery and boost it https://www.pololu.com/product/2561

MarkT

With LiPo power, 3.7V, a _good_ LDO is a reasonable solution.  Good means lots
of current handling, 0.2V or lower drop-out.  A lot of "LDO" regulators are not low-dropout
in fact, the marketing materials lie to you.  To me LDO means < 0.5V at full current.  To
many manufacturers "LDO" means "better than a 7805".

Good LDO's are fussy about their capacitors, you must read the datasheet's recommendations.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

DrAzzy

The proper way to get 3.3v depends on the source voltage, and the required current.

An LDO is just fine and appropriate for a lot of applications.

If the source voltage is 4.5-9v, you can just use a LD33V or another TO-220 regulator (or TO-223 for surface mount) for currents of 500-800mA, though the regulator will get hot, it'd be within spec. 12v will work too, as long as the current is low. I think you can do that with a LD33V powering an ESP8266 off 12v, but watch the heat on the regulator, and if you're not happy with it, you could stick one of those cheap heatsinks on with thermal epoxy (mini-heatsinks and thermal epoxy is something I recommend owning - I use mine all the time).
Always read the datasheets on regulators before you buy - and make sure you're reading the electrical properties section, not the "absolute maximum ratings" section.

If the source voltage is >3.6, you can probable find a very low dropout regulator that will do the trick, though likely with lower limits on current and/or power dissipation, and/or a higher price.

Efficiency is roughly Vout/Vin with an LDO ("roughly" because there's quintescent current and such). My father (long time electrical engineer, now retired) calls regulators "watt wasters"

If you're working with a lower voltage supply than the voltage you need, or you need to drop more than 9v or so, or wasting a bit of power is a problem (ie, you're on batteries), you want a switching DC-DC converter.

Buck/Step-Down, boost/Step-Up converters, and step-up/step-down converters, are all available on ebay for mind-bogglingly low prices. Check descriptions - it is often not clear from the listing title whether it's step-up, step-down, or both. Many of the cheap ones have no short circuit protection, and just die if you short them - so i'd recommend buying a few (they're cheap anyway).

For those who are independently wealthy, DC-DC converters are available in sealed packages, so they can be treated like any other component (some are meant to match the pinout of a TO-220 regulator) - however these cost around an order of magnitude more than the cheap, bulky, chinese ones.

Efficiency is in the order of 80-98% with DC/DC converters.

ATTinyCore and megaTinyCore for all ATtiny, DxCore for DA/DB-series! github.com/SpenceKonde
http://drazzy.com/package_drazzy.com_index.json
ATtiny breakouts, mosfets, awesome prototyping board in my store http://tindie.com/stores/DrAzzy

Wawa

#5
Apr 16, 2015, 11:04 pm Last Edit: Apr 16, 2015, 11:32 pm by Wawa
If you have to design a battery powered device, it's hard to ignore the new generation of small buck converters (boost and buck/boost are usually less efficient).
As always, measure the powerdraw of your device, read datasheets, and do the calculations.
Sometimes you just have to use a lineair regulator. e.g. with a receiver or preamp.
Because switching regulators can be "dirty devices", although small/new devices do better than their older LMxx cousins because of smaller sizes and higher switching frequencies.

Some real world testing here.
Almost 50% longer burn time from 6AA batteries (post#80).
Leo..


Zealot

Thanks a lot guys for all this info!! Now I have to go read your links ... ;-)

Go Up