PWM help please
You are correct on your understanding of "switched mode" versus linear.
My confusion of the purpose of this circuit is because a "zero fossil fuel" circuit which requires electricity to run it, that comes from a coal/oil/gas fired power station is far from "zero fossil fuel"!
I assume you have seen these forums:
http://www.oupower.com/phpBB2/
This is also interesting:
http://www.hhoforums.com/showthread.php?t=3364&page=2
I cannot be sure without a detailed analysis, which I haven't time for at the moment, but I think that either circuit will work in switching mode, not linear. While the boxes people have made have large heatsinks on them, that is needed to simply handle the power during switching. When the transistor turns on and off it dissipates considerable power so you want to do that as quickly as possible. The two circuits you have don't do that - the drive is a very poor design.
This circuit is an addition to speed up the transistor switching to reduce heat by using a proper FET driver:
**broken link removed**
This is the schematic:
**broken link removed**
It is in addition to the main PCB.
I wonder if the improved circuit you have seen is actually one which includes a better FET driver, rather than one which prevents "linear" operation. I think there is a bit of "mis-information" being used.
You may get some better answers posting on some of the specific forums where people have built the circuit.
Keith.