"Commander Kinsey" wrote in message
news
On Tue, 04 May 2021 18:33:20 +0100, Rod Speed
wrote:



"Fredxx" wrote in message
...
On 04/05/2021 13:23, 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.

PWM is the cheapest way as it needs no other component.

For a small improvement in efficiency then a constant current source
would
be best but obviously costs more.

Doesnt necessarily cost anything more at all with leds. Same price as
voltage regulators.

But if I buy a "dimmable LED" lightbulb, I can dim it with a dimmer that's
on the wall, at 240V AC. Is there electronics inside the bulb sensing the
PWM from the dimmer and using that to control its internal current
limiter?

I was talking about led bulbs that dim without a dimmer thats on the
wall. The dimmer is internal and just has a current regulator instead
of a voltage regulator that costs the same. No PWM involved.