I want to run Raspberry Pi using a general non-rechargeable 9v battery. Raspberry Pi needs 3.5W and 5V input. Questions:
- Which LDO should i use ?
For what amount of time general 9V battery is able to supply 3.5watt power ?
EDIT1:Battery is Duracell 9V rectangular battery.
Answer
The data sheet available on this page won't tell you outright but it'll hint at very bad news.
It shows that at a power draw of 0.25W the service life would be 14 hours. However at 0.5W the life falls to - not 7 hours, but 3.5 hours. This shows that pushing the battery beyond its limits results in useful life much shorter than a simple amp-hour calculation would suggest.
Double the power 3 more times and if the same pattern applies, the projected life would be more like 4 minutes than the 36 minutes that Samuel suggested.
Find a battery with your current requirements at least on its design spec. Even four AA cells would a closer match for your needs.
Alternative approach : ditch the R-Pi and use a lower power target processor. This depends on your computational needs, but there are low cost ARM processors like the TI Stellaris and others, with maybe 10% of the processor speed but capable of running at a few ma and sleeping at a few microamps for maybe a year on that battery.
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