On Tue, 04 May 2021 17:03:04 +0100, Clare Snyder wrote:

On Tue, 4 May 2021 13:23:09 +0100, "Brian Gaff \(Sofa\)"
wrote:

OK what do they use then, All I remember from my brief experience trying to
dim leds was that the most successful way of doing that was by duty cycle,
ie on to off times with them driven by some kind of oscillator with variable
mark space ratios. However it is obvious that even the briefest of ons and
the longest offs tends to still be visible in most cases, and not terribly
accurate if many leds are used as the load, there being a spread of
linearity in any given number.
Brian
Dimming LEDs in a FC circuit can be very linear right down to almost
out. On an AC circuit running at 60HZ the resolution gets pretty
rough. The switching rate is only 60 times per second so the on/off
ratio is pretty limitted whether using rizing edge, falling edge or
zero crossing switching -

With DC the switching rate can be whatever the engineer wants, and
the mark space ratio (duty cycle) can also be manipulated quite
successfully

As for "Rev Limiters" in the subject I ASS U ME the original question
was aboput engine rev limiters and how the engine "hunts" on the
limiter. This is due to Fuel Cut being used to limit the speed and it
being an "all or nothing" process - fuel injection shuts off at a
programmed RPM and comes back on when the RPM drops to a lower
programmed RPM. It is theoretically possible to make a smooth cut-off
but it is programattically complex - and for what advantage???
The "choppy" rev limitter lets the driver know he has hit it - a soft
limit would tempt an agressive driver to stay "on the limit"
constantly (like a diesel truck on the governor)

An aggressive driver would soon realise that staying on the limiter is well past the peak of the power curve, so he'd end up going slower.

--
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