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5v power supply

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You make absolutely no mention of how much current your circuit will require at 5 volts? You also make no mention of exactly what 5 volt battery you have in mind? More than likely the answer is yes, but good luck with a simple 5 volt off the shelf battery solution.

Ron
 
Nobody makes a 5V battery. There are 6V batteries available but their voltage is not always 6V.
 
Use a 9 volt battery and a 5 volt regulator.
No.
A 9V battery quickly drops to below 7V when an ordinary 5V regulator has dropped out and does not regulate.
Use a low-dropout regulator instead that regulates perfectly when the battery has dropped to 5.5V or less.
All semiconductor manufacturers make many low-dropout 5V regulators.
 
I believe we all agree there is no 5 volt battery as I initially mentioned good luck on that one. Yes, I agree that a low dropout regulator like the LM2940 or equivalent would be a good choice. However, until the OP decides to return and actually provide more details like his current requirements and how long he expects this project to run on battery power everything seems moot. While the uC and op amp won't draw much I have no clue what a 3 volt motor etc draws? Maybe just to be on the safe side the OP should use one of these batteries. :)

That should last awhile under most light loads. :)

Ron
 
No.
A 9V battery quickly drops to below 7V when an ordinary 5V regulator has dropped out and does not regulate.
Use a low-dropout regulator instead that regulates perfectly when the battery has dropped to 5.5V or less.
All semiconductor manufacturers make many low-dropout 5V regulators.
What do you mean "NO", Even a LDR is regulater.
 
What do you mean "NO", Even a LDR is regulater.
When powered with enough voltage, a voltage regulator IC regulates extremely well.
When its input voltage is too low then it "drops out" and it DOES NOT REGULATE!
 
When powered with enough voltage, a voltage regulator IC regulates extremely well.
When its input voltage is too low then it "drops out" and it DOES NOT REGULATE!
A linear reg in dropout looks like a saturated PNP transistor. The output follows the input except it's reduced by the sat voltage of the pass transistor.

BTW: the 2940/2941 are first gen dinosaurs with the unfortunate characteristic of having "quiescent" current as high as 100mA in dropout, not a good choice for a battery powered design.
 
When powered with enough voltage, a voltage regulator IC regulates extremely well.
When its input voltage is too low then it "drops out" and it DOES NOT REGULATE!
Then you need to replace the battery so whats the problum?
 
The problum? Problam? Problim? Problom? Problem, that's it!
Then you must replace the slightly used battery that has plenty of life in it very often.
A low-dropout voltage regulator should be used.
 
The problum? Problam? Problim? Problom? Problem, that's it!
Then you must replace the slightly used battery that has plenty of life in it very often.
A low-dropout voltage regulator should be used.
And what good is a 9 volt battery with only 7 volts left in it? and how long would it last?
How would you consider that "slightly used"?
I would put it in one of my kids toys and let him drain it dry if it got that low. For something more critical than a kids toy I think I would replace it before it drains that low anyway.
 
And what good is a 9 volt battery with only 7 volts left in it? and how long would it last?
How would you consider that "slightly used"?
I would put it in one of my kids toys and let him drain it dry if it got that low. For something more critical than a kids toy I think I would replace it before it drains that low anyway.
Here is the voltage curve of a 9V alkaline battery with a 53,mA load (my FM transmitter. It drops from 9V to 7V very quickly in 2.5 hours but the battery still has plenty of power in it because it still can provide 53mA for another 10.5 hours when its voltage has dropped to 5.5V and then a low-dropout regulator fails to regulate.
 

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OK so a 9 volt battery and a regulater supplying a 50ma load will run for a long time. Thats good.
 
By a long time you mean what, 24 hours? 12? 9? 5? 4? 1?
Alkaline 9 volt batteries are one of the most energy density deficient sources of power you could chose. Super caps are lower, but they at least have the ability to be recharged 1000's of times rather than 1-10 times like a possible alkaline source.
 
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