As part of an experimental project for the developing world, based on massive improvements to cooking technologies, I need to power a small PC style fan from the heat output of a wood burning stove, probably extracted by a very small thermopile. I am looking for some design inspirations for a Switching supply that can use <600mV at 4 or more amps and switch it up to a usable voltage. It occurs to me that one could use a couple of 1.5V cells even to bootstrap the circuit, but I can't see any examples for circuits which can use <600mV.

Any suggestions ?

Many thousands of people a year, disproportionately female, die of respiratory complaints from old inefficient stoves. Modern designs, which are still simple and easy to reproduce, all but eliminate the serious internal pollution of the basic stoves and reduce the need for cooking fuel.

Steve