Alternating current and rectifiers

[pbeierle]

I was at a symposium the other day where the speaker was discussing the ability to create an AC current using a piezoelectric material, and this can be used to create or replace batteries. One of the professors stopped him and mentioned that this is not possible unless the voltage is at few volts, because it must be turned to DC by a rectifier.

I understand the concept of how to turn AC to DC using a rectifier (I have built one in the past using diodes in an electronics class) but I do not understand why the voltage has to be a few volts (I figured this was possible to smaller voltages, as long as the diod's cutoff voltage is small enough). Does anyone have any ideas?

 

[Enthalpy]

Diodes begin to conduct at a minimum forward voltage, like 0.6V for P/N silicon, 0.4V for Schottky silicon, 0.3V for P/N germanium, more for SiC, far less for one out-fashioned silicon type. Below (twice) this voltage, a rectifying bridge doesn't conduct, nothing exits.

BUT.

- Transformers exist for over a century.

- Piezo elements tend to produce a high voltage, for instance in gas igniters. Or they can be built to produce more voltage and less charge, with the proper form, and series connected elements.

- MOS transistors make excellent rectifiers for very low voltage. Just drive their gate according to the instantaneous AC voltage. Any computer has them to supply the Cpu with around 1V and 100A, which arrive at the motherboard through reasonable wires as 12V, and is down-converted immediately at the Cpu.

Remove some dust from this professor, maybe?