Very Low Power Switched Mode Power Supply

This has been discussed here, albeit some time ago. The only difficult part is getting the thing to start up. If you don't mind including a rechargeable battery there's no real problem; otherwise you've got to go for an inverter based on normally "on" parts, like junction FETs or depletion mode MOSFETs.

I've not worked on the problem, so this is just what I remember, and isn't all that reliable. Win Hill and Joerg might know more - they did chime in on the 31 May 2006 thread "Low voltage step up design?"

-- Bill Sloman, Nijmegen

There are plenty of step-up chips that start at less than a volt but they usually have one thing in common: They do require a bit of quiescent from the output side, mostly a few ten uA. That can be a problem in battery apps where you have to guarantee a continuous and stable output voltage. Browse National or TI, take a look around their step-up switcher chips.

If power consumption is a really tough issue you are often back to the old JFET and have to coax it into a burst mode where the length of the bursts depend on whether the output voltage has dropped below a lower window limit or not. IOW it's going to have hysteretic behavior.

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The basic two transistor multivibrator oscillator will start and run as low as about 0.8V. Using one of those you can make a simple booster supply to run the control electronics on. A cross coupled pair of 2N2222s and a transformer can get you a 10V supply to run stuff on.

The main supplies pass elements can be MOSFETS or BJTs.

Check L6920 from ST.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

There are a number of IC "single cell" SMPS chips which will step up your 1V to something more reasonable such as 3.3V or 5V. Iq of 100uA perhaps. You could then use that supply to power a more beefy DC-DC converter to supply whatever current you want. Once you get below

800mV or so minimum require start-up voltage(depending in part on what you require in terms of temperature range at the lower end) things get more difficult.

Best regards, Spehro Pefhany

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Texas TPS61200 - 0.3v min input

A chopper oscillator built with germanium transistors ( = not for production these days!) will run as low as 0.4V.

There was an article in an old Electronics Now, by Fred Nachbaur, of such a circuit for single photocell use. I have it around here somewhere, and it might be referenced on Fred's website somewhere.

Tim

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But watch out, IIRC it's 70uA quiescent, taken from the output cap. I wrote TI support a while ago about some tricks and whether they'd be kosher. Well, that was a couple months ago and I could not even get tech support to answer. Four (!) reminders, four promises to get back to me "soon", then zilch. That tells me something I'd have to keep in mind for future design decisions ...

Hello TI, anyone listening?

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** The heading and the Q are in direct contradiction.

...... Phil

Well, if ter is a reasonable market for your improved design, get some fab house to make them and then undersell TI and market as "!Banned by TI!".

IMHO there isn't much of a market (yet). But there certainly won't be one developing if you can't obtain important info on available chips. Anyhow, most people in this field do that the old fashioned way. That would be a small helper circuit with a JFET and then a traditional switcher. If PHEMTs and stuff would be lower in cost we'd use them. But they cost a lot so mostly it's jelly-bean JFETs.

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