# Single cell AAA to 24V @ ~20mA

#### Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

•  Subject
• Author
• Posted on
I've done some searching for a canned single cell boost circuit that
can make 24V from a single AA alkaline, or rechargable AA cell. (1V min
Vin)

Outputs is ~20mA but it is only applied for about 10 seconds a couple
times a day.

I can fine single cell to 3.3 and 5V all day but 24v or even 12V is a
high factor.

I could roll my own with a flyback with a high turns ratio but I would
prefer a canned solution of it exists.

I also wasn't too keen on cascading power sections (1=>5 then 5=>24)
but that may also be an option.

any thoughts?

Re: Single cell AAA to 24V @ ~20mA
mook Jonhon wrote:

Any thoughts?

Why not use 2 cheap 23A12 12V alkaline batteries in series.
Maybe even takes less space than an AAA plus converter,

Re: Single cell AAA to 24V @ ~20mA

I need the 24V to be somewhat regulated with varying current loads and
over the life of the battery.   Doesnt need to be Super stiff but +/-1V
or so until the battery discharges below 1V.  then it can shut down.

http://data.energizer.com/pdfs/a23.pdf

Looks like these will fall off 12V fairly quickly with use.
The Ah rating is down to 6V

Looking at the mAh charts and figures for discharg to 6V (1/2

0.5mA = 115hours
2mA   = 28 hours
5mA   = 9 hours
10mA  = 3.5 hours
15mA  = 2 hours

I'll extrapolate here
20mA  = 1 hour to reach 6V

looking at the shape of the chart and assuming a similar S shape I move
the 6V y intercept from 115 to 1.

I'll assume 10.5V is my minimum which crossed about 1/3 of the way to
the 6V cutoff time.

so 1/3 of 1 hour at 20mA should be 10.5V (neglecting internal
resistance, etc)

which would be 20m minutes.

At 10 seconds/use that would be 120 uses.  at 5 uses / day that would
be ~ 1 month/ battery.

hmmm....  might be reasonable of the internal source resistance is OK.

same analysis for the AA battery.  (duracell has a better datasheet)

24V at 20mA is 480mW.

assume boost supply efficiency of 80%.  = 600mW draw from the battery

at 1.5V = 400mA
at 1V   = 600mA

assume 500mA to simplify calcs.

Run time to 1V at 500mA is  ~ 2.5 hours

assuming 10s/use and 5 times a day.  That should give 900 uses or
180days of use.   1 AA every 6 months would be more than acceptable.

Sorry for the long response,  Just thinking out loud to make sure a
simple solution, that i honestly hadn't consered, would not work for
this applicaiton.

Thanks for thaking time to suggest something though!   If you have any

Re: Single cell AAA to 24V @ ~20mA
mook Jonhon wrote:

Personally I gave up on AA/AAA, and only use lipo in new designs
For 1\$88
https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=3.7+to+24+V+boost+converter&_sacat=0
plenty choise, use a small lipo 1Ah, 80% converter efficiency, why not.
And then add a MCP73831T charge chip and recharge from USB.

Use lipos with internal protection.
https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=3.7V+1E+lipo+protection&_sacat=0&LH_TitleDesc=0&_osacat=0&_odkw=3.7+lipo+protection&LH_TitleDesc=0
scroll a bit for deals, 4 x 800mAh for 13\$, etc

Re: Single cell AAA to 24V @ ~20mA
wrote:

Depending on what you're doing LiFePO4 is likely a better chemistry
than LiPo, though it does require different chargers.

Re: Single cell AAA to 24V @ ~20mA
On 14/07/2018 11:47, mook Jonhon wrote:

At 1V gets hard to find fets that switch well, you may find one of
Diodes/Zetex low saturation voltage BJTs is a better fit, as in:

<https://www.dropbox.com/s/lv5efgm3t1k9fmv/simple_boost.pdf?raw=1

piglet

Re: Single cell AAA to 24V @ ~20mA
Piglet wrote:

Cool circuit.  I'll have to play with it in spice.

So you pull down on\  the PNP flows current and turns in the Npn.

Then the NPN pulls current from the inductor and from teh RC-feedback
to
the PNP drive which further turns it on.

What causes the switch to turn off and throw current into the
capacitor?
Inductor saturation?
VCE sat build up on the NPN coupling back to the PNP?

How do yo tune the switchin frequency?.... besides carefully.  :)

Yup fets at 1V are nearly a no go expecially at the currents requred
from the 1V.

I was hoping to find suggestions for something like this but with a
higher voltage output.

Re: Single cell AAA to 24V @ ~20mA
On 14/07/2018 18:25, mook Jonhon wrote:

It is basically a constant on time converter so the switching rate is
highly load dependent. You correctly describe the switching on process -
then once the timing capacitor has charged the PNP begins to switch off
which in turn begins to turn off the NPN and is made snappy by positive
feedback. It is a useful circuit to know for uncritical conversion at
levels of tens of milliwatts to about one watt where the load current
does not vary wildly.

piglet

Re: Single cell AAA to 24V @ ~20mA
On 07/14/2018 02:15 PM, Piglet wrote:

Looks similar to the circuit used in some of those inexpensive solar
garden lamps that use a small panel and a single NiCad cell for storage

Re: Single cell AAA to 24V @ ~20mA
On Sunday, 15 July 2018 03:59:49 UTC+1, bitrex  wrote:

-

the chip in those is usually the QX5252. Max pin voltage = 5.5v, i_out 3-
300mA.

NT

Re: Single cell AAA to 24V @ ~20mA
On Saturday, July 14, 2018 at 11:54:21 AM UTC-4, piglet wrote:

Is the ON node tied to low/gnd to turn it on?

George H.

Re: Single cell AAA to 24V @ ~20mA
On 15/07/2018 06:06, George Herold wrote:

Yes, and high or float to shutdown.

piglet

Re: Single cell AAA to 24V @ ~20mA
On 07/14/2018 06:47 AM, mook Jonhon wrote:

For such a small amount of power intermittently I think the closest
thing to a "canned solution" would be the two-stage boost, a chip with a
low Vmin first to go from as low as 0.5 to 5 and then 5 to 24.

If you need it yesterday then I think that will work fine and is the way
to go, you can buy little breakouts for a couple bucks with all the SMT
stuff including inductors wired up appropriately and drop the two of
them onto a set of protoboard or PCB pin headers.

Re: Single cell AAA to 24V @ ~20mA
On 14/07/2018 11:47, mook Jonhon wrote:

Does it have to run off a single AA cell? Life would be much easier if
you could accommodate a 9v battery and a more modest multiplier.

--
Regards,
Martin Brown

Re: Single cell AAA to 24V @ ~20mA
On 7/16/2018 6:06 AM, Martin Brown wrote:

Rechargeable 9V Lithiums have a pair of cells and all the protection stuff.
Wonder if the extra size isn't less than all the stuff you have to
use to make an AA work?