Re: really low power transistors

John Larkin wrote:
On Fri, 19 Dec 2008 18:49:06 -0800 (PST), mrdarrett@xxxxxxxxx wrote:

On Dec 19, 4:19 pm, Tim Wescott <t...@xxxxxxxxxxxxxxxx> wrote:
On Fri, 19 Dec 2008 13:45:04 -0800, mrdarrett wrote:
Anyone recommend any NPN transistors with around 0.1-0.3VBE sat. ?
I did a mouser search but apparently Vbe sat. isn't a commonly specified
parameter... ?
Thanks,
Michael
Base to emitter voltage at saturation?

Yes, that.


Or do you mean Vce_sat, the _collector_ to emitter voltage at saturation?

No, not that.

Zetex and others make the latter in small sizes. The former can't be
done in silicon.

Ah.

Mr. Larkin had an interesting idea. If I wanted to say power a boost
converter (0.1 V to 1V) could I just feed the 0.1V to the base of my,
eh, 2N3904 NPN and it would work (at just incredibly low efficiency,
since it's not in saturation)?


0.1 volts on the base of a bipolar wouldn't do much of anything.

A 0.1 volt input boost converter would be a challenge. The easy way
would be to bootstrap it with a battery. Or a solar cell.


0.1V might be a challenge but I did get one to work at 0.2V without resorting to legacy Ge devices. I used the snappiest JFET I could find. You need all the gain you can get to make the things start up. Not ye olde J309.


You might be able to make an oscillator, at 0.1 volts, from a
depletion-mode gaasfet. Maybe.


There are also zero volt threshold MOSFETs, Mouser has them (or at least used to).


Too bad you can't get tunnel diodes any more.


That really angered me as a kid. Almost every cookbook contained oscillators with tunnel diodes and unijunction transistors and there was no way for anyone to buy those unless your name was Rockefeller.

--
Regards, Joerg

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