Am I right in thinking no low voltage semiconductor device can work ( even a DC-DC step up oscillator) if the voltage available is less than the semiconductor forward voltage (0.7 for silicon0.3 for germanium)?
AJH
Simplistically yes but in practice some devices can exhibit (desirable) non linear effects at lower voltages that can be sufficient to get oscillation going to boost voltages to a level where conventional devices can then operate. I once saw a demonstration by our resident 'mad professor' at work of a GaAsfet used in this way that would run on the voltage from a single thermocouple junction cooled with freezer spray but cannot recall the details.
Define 'work'.
We've all got stuff that 'works' with microvolts (any radio/tv/mobile phone) at its input, but the supply voltage is 1.2V - 5V (ish!).
HTH
Avpx
+1 ..I can remember something similar in a textbook or summat.
not sure that FETS can't go down lower as well..a typical FET has no 'on' voltage, so to speak.
A quick google discovers that mosfets with a gate voltage of 0V and a drain voltage of 0.1V can and are available.
Years ago I designed a solar charger that would run down to something like 0.2v, using geraniums. They dont have the hard cutoff of silicon, and can operate very low, for a limited definition of operate. IIRC some can conduct down as low as 50mV.
NT
Would that be "flower power"?
John
Yes I have a commercial led torch that has a circuit like this and the AA cell is lasting well. My original question was because I assumed as soon as the cell dropped below about .7V it would stop working.
Thanks for all replies.
AJH
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