Low Power Regulators

[Charlie]

I've read that the 18650s typically loose 4 to 5% voltage on the shelf the first month after a complete charge, and about 2% every month thereafter. (Cant vouch for the exact figures).

Anand

It's hard to find exact figures, but in this article http://www.powerstream.com/18650-hig...harge-rate.htm they quote a Samsung spec at nearly 10% self discharge per month. So maybe fine for your digital camera, but wrong choice for something like a remote sensor that can't be recovered or recharged for many months. Not all lithium technologies have the same attributes. There are some that have very stable output voltage and last for 20 years at low discharge rates. And there are some, like the one you keep promoting, that the voltage changes nearly 30% while it self discharges in well under a year. But you CAN recharge it - so in many applications, it's a better choice. That's why I keep asking about the application (and not getting an answer so I'll stop now). Ultimately there are many solutions each with advantages and disadvantages. If we keep visualizing different requirements, we will keep suggesting different solutions. Without a target, how do you know if you hit it?

[andybarrett1]

Charlie

Totally missed you asking (My Bad).

Application is 818, 1307RTC and 1620LCD. No Analogs. One vibration sensor DI as interrupt.

Wakes up on vibration. Displays time for 20Seconds Goes back to sleep.... Time stamp is recorded on remote DVD System by a camera.

At moment all running from a pp3 9volt .. LDO reg and 5volts. Looking to drop to 3.3v and use a better source of power.

Hope that explains enough ??

Thanks all for reading.

[Ioannis]

You said there is room for two AA batteries if I understood right. With just one battery and the following suggestion you will have more working time on 3.3 volts draining an AA alkaline really flat.

http://www.picbasic.co.uk/forum/show...836#post131836

Ioannis

[Charlie]

Both the RTC and LCD are 5V devices - RTC min is 4.5V, LCD min is 4.7 V.
So you really can't run your circuit at 3.3 V.
You will either need to use Ioannis' suggestion (which I also recommend), or go back to your 2936 regulator with at least a 6V battery. The 9V batteries have pretty low capacity - you might be better off with a couple 3V button cells; I have not worked out the details on those.

[AvionicsMaster1]

I'm just curious and was wondering:

MAX1620/MAX1621 states it can use a range of voltage between 3 to 5.5 volts.
DS1390 states it can do 2.97 to 5.5 volts.
16LF818 states it can do up to 2 to 5.5 volts.

So with maybe a little parts massaging you could use a 3.7 battery. Though pricey and needing a connection could you use two of these or something similar to get the life you desire? http://www.newark.com/dantona-indust...mah/dp/14N3902 They are thinner than a 9 volt battery so two could fit where one 9 volt battery currently resides.

[andybarrett1]

Both the RTC and LCD are 5V devices - RTC min is 4.5V, LCD min is 4.7 V.
So you really can't run your circuit at 3.3 V.
You will either need to use Ioannis' suggestion (which I also recommend), or go back to your 2936 regulator with at least a 6V battery. The 9V batteries have pretty low capacity - you might be better off with a couple 3V button cells; I have not worked out the details on those.

Hi yes the present circuit is built around a 5v supply....BUT :-

Looking to upgrade using LF818/19, LCD 3.3v and different RTC ...1307 has lousy timekeeping :-(

Application remains same... just maybe different parts!

BR
Andy

[Charlie]

Hi yes the present circuit is built around a 5v supply....BUT :-

Looking to upgrade using LF818/19, LCD 3.3v and different RTC ...1307 has lousy timekeeping :-(

Application remains same... just maybe different parts!

BR
Andy

You'll need to choose those parts to know your supply tolerance. The answers are all in the data sheets.