I have a device that does not charge the battery anymore (battery is good). I tracked down the component that regulates the incoming charge going to the battery and, it appears to be a sot23 5-lead. Testing it, 5vdc (from USB source) is coming into the sot but nothing is coming out. The schematic is not available. I know the correct output to the battery should be 4.1vdc. The only marking on the component is the number "3308". When I'm looking for a replacement at a supplier website, what do I search on? Is the polarity of the output voltage important? Also, 3 of the terminals are vin, vout, and gnd. What do the other two terminals do in this application?

 

No schematic, no part number, and no information on what you're charging? It will be a matter of luck if anybody knows the answers to this one.

Low dropout, SOT23-5, voltage regulator...

 

Yeah, and on exactly the same question you can't answer. Imagine that!

 

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Au, contrare.... I spent 25 years working as an application engineer at national Semiconductor. I can personally guarantee you there are millions of fools who can NOT read a data sheet and figure out which end of the part to solder to ground.

I have a device that does not charge the battery anymore (battery is good). I tracked down the component that regulates the incoming charge going to the battery and, it appears to be a sot23 5-lead. Testing it, 5vdc (from USB source) is coming into the sot but nothing is coming out. The schematic is not available. I know the correct output to the battery should be 4.1vdc.

You have 0.9V of drop across the part. You need a LDO linear. You could use something like the LP2981-adj set to 4.1V.

http://www.datasheetcatalog.org/datasheets2/35/354529_1.pdf