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 Posted: Apr 26, 2012 - 07:19 AM |
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Joined: Jul 20, 2009
Posts: 42
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I will manage the software to save power to the max I can and use 3 batteries.
Option1:
Lets say we use 1117-3.3V. So 3.3 + 1.2 (drop out vtg) = 4.5.Then 4.5/3 = 1.5, below which the circuit wont work. So this option does not look great.
Option2:
By series voltage regulator, did you mean this http://www.tpub.com/neets/book7/27k.htm (^_^ correct me if I am wrong here)
Can I use PN2222 for this? Its Vce(sat) is 1V as mentioned in the datasheet.
So it will be 2.8 + 1 = 3.8. 3.8/3 = ~1.3V (Assuming the lcd and controller works at 2.8V  )
How does this sound ? |
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Posted: Apr 26, 2012 - 08:58 AM |
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Joined: Jul 02, 2005
Posts: 5941
Location: Melbourne, Australia
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The Texas Instruments TPS79933DDC low drop out 3.3volt linear regulator has a 200 mA load limit. Drop out is 0.1 volts. You can even ask for a sample. QED.
3.3 + .1 = 3.4 ... or 3.4/3 = 1.13 volts per cell.
Cheers,
Ross |
_________________
Ross McKenzie
ValuSoft
Melbourne Australia
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Posted: Apr 26, 2012 - 11:17 AM |
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Joined: Jul 20, 2009
Posts: 42
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hey thanx valusoft,
I need to chk if it is locally available as I am making a product. I doubt it though.
Also need to check the cost.
But ya, extremely low dropout vtg regulators could be a great option.
Anyone from India aware of same available locally? |
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Posted: Apr 26, 2012 - 01:43 PM |
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Joined: Jul 02, 2005
Posts: 5941
Location: Melbourne, Australia
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Posted: Apr 28, 2012 - 05:47 AM |
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Joined: Dec 06, 2007
Posts: 2512
Location: Redmond, WA USA
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gregsmithcts wrote:
A diode (early) in the power circuit will prevent cock ups.
Salt Petre was rumored to do the same, or have I mistranslated the Bristolian again. |
_________________
Larry
Those afraid to embrace the future will quickly fade into the past. - larryvc
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Posted: Apr 28, 2012 - 11:57 AM |
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Joined: Oct 30, 2002
Posts: 5720
Location: The Netherlands
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A voltage regulator consumes power too for its own purposes. It could overwhelm the power used by the MCU when it's in a deep sleep mode.
The aforementioned TPS79933DDC needs 40uA for itself; which is not bad at all, considering a plain 7805 needs ~7mA
Of course, this might not be a problem for your application. |
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Posted: Apr 30, 2012 - 04:50 AM |
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Joined: Jul 20, 2009
Posts: 42
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Hey guys,
Got the PCB. Did first test.
I have posted the schematic.
1. Power source : 2 x AA batteries. (No vtg reg)
2. LED1 = OFF.
3. LCD Backlight = ON. (No PWM)(82E resistor)
4. Current : Initiallay it took 9mA and dropped by 0.1 mA every few minutes. The display was working till 6-7 hours.
With LCD Backlight Off it starts at 8 mA.
Will mail TI today for TPS79933DDC. |
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Posted: Apr 30, 2012 - 12:04 PM |
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Joined: Jun 27, 2005
Posts: 3412
Location: St.Petersburg, Russia
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Could you use a
http://en.wikipedia.org/wiki/Joule_thief
in your design? It's ridiculously simple, but it will not cut manufacturing costs. It will save a lot of batteries though. |
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The Dark Boxes are coming.
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