On Thu, 20 Dec 2018 16:19:47 -0000, trader_4 wrote:

On Wednesday, December 19, 2018 at 11:03:21 PM UTC-5, Clare Snyder wrote:
On Wed, 19 Dec 2018 12:49:47 -0000, "William Gothberg" "William
wrote:

On Wed, 19 Dec 2018 12:28:04 -0000, Rod Speed wrote:



"William Gothberg" "William wrote in message
news On Wed, 19 Dec 2018 11:51:35 -0000, Rod Speed
wrote:

William Gothberg "William wrote

Do switch mode power supplies flicker in time with mains?

No.

Specifically LED power supplies in commercially available domestic
lamps.

None of mine flicker at all.

By in time, I don't mean at the same 50/60Hz, but anchored to it. I.e.
if
you have several such lamps each with their own built in supply, will
they
all flicker in time, using the mains frequency to keep them in time, or
will they be random, making the room overall not flicker due to them all
being random?

None of mine flicker at all.

And is there any way I can test this?

Yes, Get or make a strobe disk or use
one of the original LP disks that has
a strobe disk on it and see what it looks
like with the lights illuminating it. You'll
get it appearing to freeze when rotating
if the light level is varying in synch with
the mains frequency.

I tried taking photos of them, but my camera only goes as fast as
1/2000th
of a second, which shows all the lights at the same brightness each
time,
I suspect the flicker is above 2000Hz.

Or they don't flicker at all. No reason why a proper
switched mode power supply needs to have any
AC component at all on its output. The cruder
ones may well do.

They probably are fairly crude. I know they flicker, for example if I use
my cordless drill, the chuck appears to spin the wrong way under the LED
lighting.

But it's nothing like as low as 50Hz. What I want to know is if the
higher frequency they're flickering at is anchored with the rise of the AC
wave.

No its not.

I.e. will all the LED lights in the room flicker at precisely the same
time, or will they be out of synch (due to tolerances in the circuitry of
each PSU)

Due to it not being synched with the mains, actually.

I meant if the PSUs were absolutely identical, and all the lights were switched on at the same time (with one lightswitch), they should remain in synch forever. But since there are tolerances in all the components in the PSUs, they won't stay in time.


Forget the component tolerances. Two mechanical light switches can't be
synced to turn on the power at exactly the same time, anywhere close
enough to sync them up to begin with.

Er.... I have more than one light running off one switch, many people do. A large room normally has more than one light fixture, or a fixture with several bulbs in it.

You would need electronic
switches driven by a common signal. And even then, even with components
of sufficient tolerance, which is impossible, I'm not sure it would work.
First thing that comes to mind is the freq source, which I'm guessing
is a crystal. You could have crystals with theoretically identical
frequencies, but I'm not sure that means they will start oscillating
at exactly the same instant so there is no phase difference.