Cell Phone "AA" BATTERY Replacement...

[NewToElectronics]

The Lithium-Ion rechargable battery that is made to fit in your cell phone is 3.7V. Most people use it and charge it with the charger that is made for it. Why don't you?

Really?!? I had no idea. Maybe I should do that. I don't think that's really a feasible idea for me (just kidding). I always have to do things the backwards way first and then realize there is a reason for doing it the way it is done in the first place. That, unfortunately, is the only way I learn...
Yours Truly,
College of Hard-Knocks Graduate

 

[NewToElectronics]

Be careful here...

Yes, it's a boost converter, but by definition, a boost converters output will always be bigger than it's input. Just because it says the input range is to 5V, doesn't mean you can put 5V in and get 3.7V out... won't happen. Your input voltage would have to be less than 3.7V. Also, you don't "have to use" the "on-board" LDO. The internal "switch" is good for 1A, so you can get more than 200mA out of it.

But the specs quote max voltage = min voltage = preset voltage = 3.6V. I thought that no matter what voltage you put in from 1.8V to 5.5V, you would always get 3.6V period. If this isn't the case, what kind-of voltage do you expect to get from a 5.5V input? I wasn't too concerned about getting a boost converter so much as getting a voltage regulator that was capable of being efficient, as well as creating a constant voltage at 3.6V.

Also, what is LDO?

 

[NewToElectronics]

Audioguru, I'm starting to see your wisdom in your recommendation to use the rechargeable battery that came with my phone. However, my morbid curiosity is getting the better of me here. I noticed an LC circuit in between the battery input for this chip (TPS61122, switching boost converter) and the SWN and SWP inputs. The SWP is the DC/DC rectifying switch input and SWN is the DC/DC switch input.
What does this LC circuit accomplish?

http://focus.ti.com/lit/ds/symlink/tps61122.pdf

View attachment 39576

 

[audioguru2]

The voltage-boosting IC is a switched-mode power supply. Its oscillator grounds one end of the coil with the other end at the input voltage which builds magnetism in the coil, then releases the coil and it makes a "flyback" higher voltage which is stored as the boosted voltage.

An ordinary linear voltage regulator needs its input voltage at least 2.5V higher than its regulated output voltage. This IC's LDO (low dropout) regulator needs its input voltage to be only at least 0.3V higher than its regulated output voltage.