Boost Converter

0.4VDC ??? ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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I love to cook with wine.     Sometimes I even put it in the food.

DigiKey -> product index -> integrated circuits -> PMIC - Voltage Regulators - DC DC Switching Regulators

Then search on a minimum voltage from 0 to 0.4V.

You'll be disappointed -- I only found two part numbers.

0.4V is an obnoxiously low voltage for this -- it's hard to get transistors that'll work at this voltage, much less work well. I kind of have the notion you're doing this from solar cells -- can you run two in series?

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I think Jan P has posted some inverters that run from millivolt inputs. Jfets, I think.

Somebody, maybe LTC, has a low voltage booster chip.

I'd consider using a lithium primary battery to bootstrap the startup of a simple boost converter. The battery might last several decades.

Such low input voltages are a common problem for energy harvesting and self powered sensor systems. Googling for these buzzwords, I found:

"Ultra-Low-Voltage Input Power Converters Support Energy Harvesting" etc... 20 mv input voltage. Ok, I'm impressed.

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I designed a little boost converter a while back that used one of those ISDN transformers that could operate from a very low voltage - it used a single transistor blocking oscillator wired to part of the primary to get the thing started, and then the main converter was like one of those things where you switch the center tap of a transformer, where the other two taps are connected in series with the load.

I don't think it ever made it out of LTSpice, but I think I still have the file around here somewhere.

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The ISDNs are great little xfmrs. We use thousands of a Talema

1:1:2:2, which has all sorts of uses. Did you get a bipolar transistor oscillator to start at 0.4 volts?

A small PHEMT would be cool, even better than Jan's jfet maybe.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Harvesting is the right keyword here. Or fuel cell converter. There are enough ICs available to get 20mA done.

If it has to be cheap: A JFET oscillator makes several volts as a control voltage, to operate a regular run-of-the-mills switcher and house-keeping stuff or maybe milk the whole 20mA out of it by paralleling JFETs. I got a BF862 in an oscillator hook-up to reliably start around 300-400mV. If not enough oomph and you don't want to parallel too many JFETs follow this with an "intermediate" helper converter that is switched by this oscillator. OldGuy would be done latest at this stage.

For those who need more power:

That drives a classic converter IC with some big old FETs and you can create almost any voltage at high power levels. Years ago we had a bet going on a German NG that you can get >90% efficiency. I put my bet in the "Yes, we can" hat, others said "impossible". Help in all shapes and forms was allowed. Then the OP did most of the design and prototype but it was in modern speak a "crowd design" with most of us pitching in. He got well over 90% out of it. One of the guys (who had bet against it) said if he loses he'll do a kegger at his company. I am sure he would have but most of us were just too far away.

Hey, how old is "Old"? Isn't 60 the new 40?

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[snip] 75 is the new 50 ;-)

(In that 3-month chip gig on Long Island a few years ago, a co-contractor thought I was 55~60... he was astonished when I said

72.) ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

| 1962 | I love to cook with wine. Sometimes I even put it in the food.

72 here also.

I remember a ~0.4 VDC boost converter circuit shown in Electronic Design or EDN many years ago. That used a single germanium transistor. Anybody got a link for that. (as a curiosity)

The easiest design for 0.4V (or less) will not involve semiconductors. It's a vibrator (electromechanical chopper), just like Model T spark systems and vacuum-tube battery radios used to use.

Can you use a high-voltage battery for control circuitry? Something like a lithium coin cell can control and bias commutating switches for a solid-state non-buzzing converter, if you don't mind replacing it every year.

The "trick" exhibited in some of the LT products is that an auxiliary battery is used to start the operation then the boosted output takes over... thus consumption from battery is nil.

Another approach is to use a battery being charged as the kick-starter. This means you mustn't let the battery discharge too low between charging operations. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Google "germanium transistor" price - heaps of them.

Hul

OldGuy wrote:

Some of the Tadiran lithium batteries have 40 year shelf lives. Makes energy harvesting seem silly.

The battery just needs to start up the converter.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

I think I used a depletion mode MOSFET. I bet a germanium bipolar would work! There's a local electronics store that still stocks real parts - they have a ton of NTE replacement PNP germanium transistors just siting around.