I was wondering if anyone could recommend some boost converters (at least that's what I believe I need). I'm building a GSM based GPS tracker that I want to connect a backup Li-Poly battery to. 90% of the circuit's voltage requirements are at or below the battery voltage with the exception of the Arduino and the DTMF decoder IC. Since I don't have any experience with boost converters I was wondering if anyone had some recommendations. I won't need more than 100mA at 5 volts. The only other thing I'm unsure of is in the data sheet for the GSM (GE865) there is a lower limit frequency threshold requirement of 500kHz if using a switching regulator. I didn't know if switching regulator specs transferred over to boost converters also or not (GSM module powered directly from the battery so was more concerned about interference downstream). Any advice would be greatly appreciated. Thanks.
This switcher won't work off of lipo, the spec'd minimum input voltage is 4.5V, the lipo would give you only 4.2V when fresh. I sell this little switcher -> http://www.circuitsathome.com/products-page/power-supplies , which will work for you. Since lipos don't like being drained below ~2.7V, you will need to make some type of undervoltage lockout circuit.
Thanks for the help guys. Kinda surprised by the input voltage requirements on the IC on Sparkfun module though...it seems very versatile but they're missing out on most of the "portable" market. I'll give the other one a try. Thanks again.