Re: Ultra-Low Power Operation

On Sun, 06 Oct 2024 17:43:47 +0100, Cursitor Doom <cd@notformail.com>
wrote:

On Sun, 06 Oct 2024 07:35:24 -0700, john larkin <JL@gct.com> wrote:
>

On Sun, 06 Oct 2024 13:28:46 +0100, Cursitor Doom <cd@notformail.com>
wrote:
>

On Sun, 6 Oct 2024 09:25:47 -0000 (UTC), piglet
<erichpwagner@hotmail.com> wrote:
>

Cursitor Doom <cd@notformail.com> wrote:

Gentlemen,
 
I vaguely recall going back the best part of 60 years now, there was a
competition among radio designers (AM in those days) to come up with
the design which would operate at the lowest possible supply voltage.
This had arisen, I would guess, as a result of the 'semiconductor
revolution' and all these designers would compete to develop a working
radio using ever more absurd Vcc levels. I'm pretty sure someone
managed to get something credible together that worked off of just
over 1 volt but can't be sure after all these years and there's
nothing I could find on the 'net about such a contest, either. But I
do remember it, for sure.
I'd just be interested to know what can be done with <1V today. Anyone
know?
 

>
Around that time there were published designs using germanium transistor
inverter to step up 250-300mV to a few volts for driving more conventional
items.
>
Complete radios built from Ge tunnel diodes were done too.
>
Silicon bipolars are constrained by 0.6/0.7V forward junction voltages but
once started can continue stepping up from much lower voltages. LT made a
boost converter IC that once started continued boosting from 100mV.
>
Depletion fets let you go much lower, Jan Panteltje has posted his 20mV
booster which lights a LED.

>
I take your point, Piglet, but many of us still have Ge devices in our
junk boxes, so need not be constrained by the greater barrier height
of their Si equivalents.
Using some sort of boost converter is not in the spirit of this quest!
The circuits that were being submitted to the design contest were all
designed to operate straight from very low DC supplies, with none of
the shenanigans you mentioned. :)
This might be a tall order, but I'd like to see a circuit for an AM
radio which could be powered from half a volt.

>
Crystal sets need no power.

>
Arguable. They don't need batteries, but do need the power of the
transmitter to produce an output.
>

There were some that rectified power from several stations to amplify
one.

>
Really? Good Lord! I've never heard of that; most resourceful!
>

>
And yes, a depletion fet or one of the zero-threshold fets could
detect and amplify at very low supply voltage.

>
Fascinating. Thanks for that. Depletion mode? I'll have to re-acquaint
myself with that. I normally use enhancement mode FETs for anything
requiring the preservation of a high Z signal. I'm not even sure what
the typical application for a depletion mode FET might be.

Depletion fets are very useful. The Supertex parts are great. I use
them as current limiters, for driving LEDs or zeners or discharging
caps.

They are great as input protectors too. See AoE3 p 361. H+H added the
source-source resistor.

The LND150/250 parts have very repeatable Idss, around 1.6 mA. Jfets
are all over the place with as much as 10:1 Idss specs.

Somebody, can't remember who, makes zero-threshold mosfets.

>

Where can you buy a half volt battery?

>
You can't buy them, but I have very many of them here, actually. I
keep forgetting to recharge them.  :)

We need a giant class-action lawsuit against people who sell batteries
that corrode and leak and destroy things.