I have a project which uses microcontrollers and a radio transmitter, both running at 5 V. The circuitry consumes less than 1 mA from the 5 V rail when idle, and 1 A when transmitting data using the radio transmitter. The transmission phases do not happen often, as the device spends most of the time in idle mode, usually transmitting only once every 24 hours for a few seconds (maximum 20 seconds).
Now I'm designing a battery input for the circuitry and I cannot decide whether to use 11 V battery packs (LiPo) with switching regulators, or LiFe batteries instead where I can get a low regulating voltage difference between input and output for the regulator (output of 6 to 7 V) and use a linear regulator with those lower voltage batteries.
Which of these setups gives more efficient results for regulation circuitry in this kind of use?
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switching regulator with 11 V input, dropping the voltage down to 5 V; or
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a linear regulator at (mostly) low current and maximum of 2 V voltage drop over it?
One of the main interests in addition to the battery life, is the simplicity of most linear regulators versus switching regulators, which reduces time spent on designing the product and saves space from the board. Switching regulators can also cause some radiation that might interfere with other circuitry and they are also more expensive.
Best Answer
Interesting question because I can see the answer going either way, depending on environmental circumstances.
Some aspects of the design which may not be immediately obvious...
1) Switchers are notoriously poor at a tiny fraction of their load - they may consume several mA internally, or they may lose regulation and deliver 7V below some value, say 1% of rated load (10mA in your case) without special care in design.
2) One answer could be a linear regulator during sleep, (even from 11V but there's nothing wrong with a 2S Li-Ion - nominally 7.4V max 8.4V) and the MPU has to wake up a switcher before transmitting. If the linear regulator only supplies a few mA, you can probably find a SOT-23 to do the job, or SOIC-8 at the largest, so I don't believe size is the issue
3) A linear regulator for 1A will need some heatsinking even for 20 seconds ... if there's a convenient chunk of metal, use it. Linear may be more reliable from its simplicity. But what happens if the TX gets stuck "on"? Running the battery flat is one thing, destroying the equipment is another... .
4) I would not, personally, change battery technology simply as a way of tuning supply voltages. If you need lower fire hazard, or greater charge/discharge cycles, or some characteristic of LiFePO4 that's a reason for using them - otherwise stick with commodity batteries for economics and simpler servicing. .