On Tue, 04 May 2021 17:03:04 +0100, Clare Snyder <
cl...@snyder.on.ca> wrote:
> On Tue, 4 May 2021 13:23:09 +0100, "Brian Gaff \(Sofa\)"
> <
bri...@blueyonder.co.uk> 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.