Russell McMahon wrote:
>
> > > Good job. But... if you publish your idea, then you can't get patent

> 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.

Actually "hippyware" but the lawyers will tell you
that still means you can use it for free if you choose.

> 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.

Exactly how I feel about it. This design works well and
NEEDS to be shared. :o)


> 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.

I think there is a blurring of the definitions of
hysteresis, phase delay, and monostable in oscillator
design. I don't like the term hysteresis here as there
is no dc hysteresis at all, only one caused by a phased
delay. As the delay period is a clearly defined RC charge
period from Rz to C1&C2, and the circuit is totally stable
during this timed OFF period, I think it is best defined
as a "monostable" type delay as used in 555 timers and
many switching regulator chips.

When the circuit hits the target output voltage it turns
OFF for a timed period.


> 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.

Good info to know. I don't mind how much money people
make from this idea provided i'm recognised as the
source. No patents needed for that.

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

> The brilliance of Roman's circuit is that it *seems* "obvious" after the
> event, but such circuits are far from obvious before they exist.

That may well be the nicest compliment I have ever
received. :o)

The "monostable" effect accounts for more than half of
the efficiency gains as it markedly slows the switching
frequency by 2x or 3x. This reduces the switching losses
compared to the amount of energy in the inductor for
each pulse, and where improving switching speed itself
(from L feedback) gives about 5% better efficiency over
the original circuit, the monostable forces much longer
off and on periods and adds another 8 to 10% improvement
in efficiency.

The C2 dump back into the Zener causes it to peak and then
re-stabilise at 5.6v, this gives a very repeatable zener
voltage for each turn off point. ie great regulation.


> 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.

Cool, i'd like to know it goes. I'm going to
fiddle tonight with a 40v to 12v design as asked
by Alexandre, and then maybe try adapting that to
higher voltages.
:o)

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