Computing stuff tied to the physical world

Running off a single AA battery

In Hardware on Sep 6, 2010 at 00:01

The other day, I found the LTC3525 – an interesting little (yes, tiny!) boost regulator chip, which might be a pretty good power source for low-power JeeNodes.

Couldn’t resist – had to try it…

Here’s a test setup using my favorite foam-board as base, with one AA battery driving a test LED:

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(hard to see, but that LED is indeed on)

Did I mention that the whole thing uses tiny parts? It did take some patience…

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Tests show that it will regulate any input voltage from 0.8V .. 5.5V to 3.3V @ 60..200 mA depending on the input voltage. And with 70..90% efficiency, even in the 10′s of µA current consumption range. I’ve verified that it will indeed down-regulate when fed > 3.3V, which makes it very flexible.

The quiescent current draw of this circuit appears to be around 20 µA on a 1.3V input.

So it looks like this could work out nicely:

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My hunch is that this thing could last 6 months for a room node. Maybe more, but with a 6-pack of AA batteries plus charger, who cares?

Hmm, might be worth designing a little board for…

  1. 3D electrical sculpture – neat… Have you seen the skeleton arduino board? http://blog.makezine.com/archive/2009/12/arduino_skeleton_-_look_mom_no_pcb.html

    That aside, the DC-DC step up SMD device looks very neat (if a little expensive).

  2. Similarly, the Lilypad power supply which feeds the whole system from a single AAA battery is based on an NCP1400-5V .

  3. If you are interested in generating other output voltages between 1.5V and 5.25V, or want fixed-frequency operation for lower noise, check out another little synchronous boost converter, the LTC3526L. It will start up at an input voltage of only 680mV and switches at 1MHz so you can use a very small inductor. It also offers very low quiescent current and the ability to “buck” down from an input that is above the output (albeit at lower efficiency). Unfortunately it’s only offered in a tiny DFN (leadless) package.

  4. Great tips. Honest, this sort of feedback is a great way to find out about alternatives and new options.

    The LTC3525 has slightly better efficiency at low current levels than the NCP1400, probably due to the synchronous rectifier, which avoids some of the loss of the Schottky diode. Also a lower quiescent current. It comes at a price, though – literally: the LTC chip costs substantially more.

    The LTC3526 is interesting too, hadn’t seen it before. Again (very) slightly higher current consumption at low values, and the DFN form factor is indeed tricky.

    A while back, I looked into the MCP1256/7/8/9 capacitive charge pump – which has a 10 µA consumption at very low power levels, but it only goes down to 1.8V, i.e. 2x AA or AAA.

    Let’s keep lookin’

  5. I can imagine a future Jeenode that has an onboard upconverter, and a battery clip for a NiMH AAA on the back.

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