In light of the fact that silicon transistors need at least half a volt to turn on at all and germanium isn't widely used anymore, how do folks design fairly complex circuits that run on a single cell that's 1.5 volts at most and delivers most of its energy closer to 1.2 volts or even lower?
This is a naive question, apologies to anybody who's annoyed.....
Thanks for reading,
bob prohaska
There's a hobby of making oscillators that will run on the lowest possible voltage. Like 10 millivolts maybe. They use jfets.
Depletion phemts might be even better.
Somebody makes a silicon IC that runs on something like 200 mV. Maxim?
Anything over 1 volt is enough for a silicon transistor circuit.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
Those keywords turned up some interesting reading,
Thank you!
bob prohaska
Any time you need crazy, I'm here to help.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
There's:
Theo
Ummh. This
photo shows a 2N3004 SCR as switching element. Are there different
2N3004 types?Pondering
Reinhard
2N3904 ?
After having activated eagle-eye mode: could be!
Many thanks
Reinhard
No one should be annoyed as it's a very good question indeed.
Well, perhaps, but it's rather challenging when just a couple of cells provide so much more leeway. To operate a BJT in CE mode (for example) you need at least 0.6V B-E forward bias, plus something more positive on the collector (talking NPN devices here). You can only hope to deal with very small input signals (in the analog realm) with such a limitation. Having a PD of only 0.4V from B-C is rather like a 6'5" man trying to fit into a Fiat 500 for anything more substantial. Or am I nuts? I've never looked into VLV design, but find it quite interesting to see how far folks have pushed it.
There are NPNs that conduct usable amount of base current at 400 mV. Linear Systems super-beta parts are even better.
Cheat and add a lithium battery to kick-start things.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
Well, Schotkey diodes have a barrier height of only about 250mV, so if there's a BJT made using Schotkey technology, that could prove useful in this kind of challenge I guess.
I'm guessing that's impossible, but it would be cool.
Fets can be had with thresholds either side of zero.
Tunnel diodes could be made to oscillate at very low voltages.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
The first mosfet must have some interesting doping, if indeed it is a mosfet.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
This must be what's used in modern gas-fired waterheaters with electronic controls but no AC line power required. I've long wondered how my new water heater works, now I've a good idea 8-)
One obvious question is how the scheme could be adapted to harvest low-voltage AC power. Might it be possible? There'd likely be some penalty, in the form of higher minimum input voltage, but maybe with a blocking capacitor and a pair of low-voltage diodes as a charge pump? The capacitors might get big....
Thanks very much for posting!
bob prohaska
I have one of those. There were multiple series thermocouples in series like little battery cells, with one end around the pilot flame and the other end to a heatsink exposed to the ambient air. This TC battery generated something like one volt, but at a pretty good current level. I may know the patent number.
Joe
Google for "Honeywell water heater gas valve thermopile" (no quotes).
Joe
AKA Frankenstat. It's a nightmare.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
I've never worried about its dreams, and it does seem to keep the water hot nicely.
Joe
It can get into an error state that can only be fixed by opening it up and shorting a supercap or something to reset the logic.
John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics
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