> > Good job. But... if you publish your idea, then you can't get patent
> > protection.
> IMHO Roman has already published his design (on the internet and on the
> piclist), and granted use under his 'hippyware' license. Although not
> easy to prove in court, this is enough to prevent him from patenting
> (you can't patent what you have already
> published)
> - prevent anyone else from patenting

In fine print at the TOP of his web page (not at the bottom where lawyers
put theirs :-) ) Roman has explicitly made the design public domain. It is
very probably worth far more as a circuit which may end up with his name on
long term than as a patent protected design. The original circuit topology
came from Richard's relay driver circuit (and I don't know where that came
from) but Roman has both re-targeted the application and refined it beyond
easy recognition. The addition of the "hysteresis" capacitor is new AFAIK
and transforms (no pun intended) the operation.

In many countries (including NZ) publication prior to patenting makes a
concept unable to be patented (and therefore public domain even when this is
not stated.) In the USA (and presumably elsewhere) you have one year AFTER
publication i which you can still file a patent. I don't know whether this
applies after you have expressly made a design public domain.

The two key points which make this circuit "special", as used in this
topology, are (IMHO)

i    the use of the transistor as a switch and comparator simultaneously (by
using the emitter as the output sense input and

ii    driving the zener reference negative with capacitor feedback when
switch-off occurs.

The first was a feature of the original circuit but the second is entirely
original. (I just checked Richard's original circuit (August 2001) to make
sure I could say that safely.)

The brilliance of Roman's circuit is that it *seems* "obvious" after the
event, but such circuits are far from obvious before they exist. Every
component has a place, operation is intuitive (unlike my 3 transistor
version which provoked protracted debate as to whether there was formal
hysteresis present) and it's not clear how one would readily improve it
without adding substantial complexity.

I can't see any reason why Roman's circuit couldn't be easily enough altered
to operate at much higher voltages. I'm about to design the next generation
of the exercise controllers which sparked my original challenge. One version
of this will still need a wide supply range high voltage buck converter.
I'll certainly try Roman's circuit to see how well it performs in this
application. (10 - 200 volts in -> 10 volts out. 0 - 500 mA out. Regulation
& efficiency not especially critical. Reliability crucial. ) I'll probably
use a PFET as the pass transistor as this greatly reduces the energy
dissipation in the drive resistor(s) at high voltages - a not insignificant
consideration.




        Russell McMahon

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