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Your favorite step-up dc-dc converters for AAs?

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shimniok

Member
Thanks in advance for taking the time. I appreciate it.

A little background -- For various projects I seem to always rely on a 9V or some AA's and a 7805. Thing is, the 7805 isn't terribly efficient (4mA quiescent draw for the ones I stocked up on) and so I started doing some research into LDO regulators and step up DC-DC converters for use with battery operated projects. I'm interested most in the switched dc-dc converter/regulator chips.

But I'm awash in all the options. I could stare at data sheets for a long time... but...

Do you have any favorites that you find flexible enough to use for a variety of projects (like the 317 or 78xx that seem to come up all the time) ?

I'd like to find something that, in order of priority,
  • has quiescent current ≤ 1mA.
  • Run off two AA's (say, ~2.5V minimum or so)
  • If it can run off a single AA, that'd be even better
  • don't care if it's big TO-220 or microscope SC70.
  • I don't care if it is smt or thru hole,
  • Low supporting part count
  • 5V -- can be adjustable or fixed
  • Cheap is better, like $1 or less.
  • I think it'd be most flexible if it can source 200-500mA

On the current... I could probably engineer around that in some cases. Like with this IR extender/repeater I am working on... I *could* run the 100mA LED(s) straight off the battery with a constant current source. So, if there's a regulator that otherwise fits but has only 50-100mA capacity, I can probably live with that.

What I've found so far...

Pololu uses a National NCP1402 on their LV168 board (which I have) and they sell a stand-alone regulator for $8 using this chip. It uses only 3 components outside of the chip (two caps and an inductor). So that's an option but it is a bit inefficient, I think, at only 84%.

Linear Tech. has a whole list... the one I settled on was perfect. Able to supply 400mA, 3 supporting components, 5V or 3.3V or 3V versions. Then I found out it isn't available anymore! :mad: They list others but don't know which are still avail. e.g., LTC3528, LTC3400, LTC3428, an so on and so forth. Loads of 'em. All > 90% efficient.

Used the National site to try and find some stuff. Was looking at the National LM27313, and LM2578A, but each requires a lot of supporting components. The 27313 is 90% efficient, and cheap at $.60 The 2578A is not so cheap at $1.42.

I've looked on Mouser to see what is there... but trying to filter down to a useful, short list has proven tough.

So hoping you have a few 'favorites' to help me focus my search a little better... thanks in advance!

Michael
 

mneary

New Member
My thoughts:

AA is denser and cheaper than 9V. More suppliers, especially NiMH.

84% isn't really horrible compared to 90%. I hope you're just recharging NiMH and it just becomes 7% shorter life.

Take a good solid layout recommendation from the supplier and follow it closely. It's easy to screw up my own.

Maybe one chip for 1-cell, one for <100mA, and one for >100mA. Run unregulated LEDs from Joule Thief?

Are you migrating to Lithium (3.7V) in the future? If so, don't stock up too much. Or, design your new (transitional) stuff as 3-AA (3.6 to 4.5V).
 

Hero999

Banned
For powering low current projects off a 9V battery there's the LM2936Z-5 which has a quiscent current of 15µA and a drop-out of just [email protected]

You can also build a simple switchig regulator with a couple of transistors..
2-transistor Black Regulator
 

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shimniok

Member
Good thoughts, thanks for the input! I saw your suggestion, Hero999, on the 2936 in another thread. Looks like a good choice for low current circuits. Will play with the discrete component circuit. Could probably do that up in SMD on a fairly small board at some point.
 

audioguru

Well-Known Member
Most Helpful Member
Many years ago Silicon Chip magazine had a project: "Never Buy A 9V Battery again". It used a TL499A PWM IC to stepup the voltage of two AA cells. The IC has a voltage regulator.

Look for the project in Google. Then buy the article from Silicon Chip magazine.
 
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Hero999

Banned
That looks like a nice IC.

The quiescent is only 80µA, when configured as a step-up regulator.

I don't know what the efficiency is or whether it's equivalent mAh from a 2500mAh pair of AAs is greater than a NiMH battery. I'd be tempted to set the output voltage to 8V rather than 9V to save power. :D

http://www.datasheetcatalog.org/datasheet/texasinstruments/tl499a.pdf
 

Hero999

Banned
The TL499A is only rated to 1.1V so it won't drain an AA cell until it's dead.
 

bountyhunter

Well-Known Member
Used the National site to try and find some stuff. Was looking at the National LM27313, and LM2578A, but each requires a lot of supporting components. The 27313 is 90% efficient, and cheap at $.60 The 2578A is not so cheap at $1.42.

I've looked on Mouser to see what is there... but trying to filter down to a useful, short list has proven tough.

So hoping you have a few 'favorites' to help me focus my search a little better... thanks in advance!

Michael
Let's see... LM27313. That data sheet looks damn familiar... oh, yeah.... I wrote it!:D Oh, well....

Anyway, it's an OK part except at lower input voltages (like below about 4V) the current limiter on the internal FET switch absolutely nose dives straight down. That means it can only do very little output power at lower ranges of VIN. Just FYI.

You would be better off using the LM2731, at least it has guaranteed current values you can hang your hat on. The 27313 is the rejects that fail when testing for the 2731.;)

LM2731 - 0.6/1.6 MHz Boost Converters With 22V Internal FET Switch in SOT-23

At least this one has specs for how much power you can get at various input voltages (which translates directly into FET switch current).
 

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shimniok

Member
thanks for the input, bountyhunter

After some more searching, and skimming through data sheets, these two may be promising.

TI TPS6122x - http://www.electro-tech-online.com/custompdfs/2009/08/tps61220.pdf

and

Exar SP6648

http://www.electro-tech-online.com/custompdfs/2009/08/sp6648.pdf

Both take very low input voltages (< 1V) and have very low quiescent current (< 15uA), and both put out heft current, > 150mA for the Exar and 400mA in some cases for the Ti device. They are both adjustable, capable of Vo=5V. Both require only a few supporting parts.

Michael
 

bountyhunter

Well-Known Member
thanks for the input, bountyhunter

After some more searching, and skimming through data sheets, these two may be promising.

TI TPS6122x - http://www.electro-tech-online.com/custompdfs/2009/08/tps61220-1.pdf

and

Exar SP6648

http://www.electro-tech-online.com/custompdfs/2009/08/sp6648-1.pdf

Both take very low input voltages (< 1V) and have very low quiescent current (< 15uA), and both put out heft current, > 150mA for the Exar and 400mA in some cases for the Ti device. They are both adjustable, capable of Vo=5V. Both require only a few supporting parts.

Michael
Those parts looks pretty good.

I recall that Maxim used to have the best selection of low power, low voltage DC DC converters. Linear Technology has some too.
 
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