Re: Light bulb power control/dimmer

In article <s701j.20108$4k.13529@xxxxxxxxxxxx>, LVMarc@xxxxxxx
says...
Spehro Pefhany wrote:
On Sun, 18 Nov 2007 17:16:22 +0000 (UTC), the renowned
don@xxxxxxxxxxxxxx (Don Klipstein) wrote:


In article <pan.2007.11.16.21.28.25.395724@xxxxxxxxxxx>, Nobody wrote:

On Fri, 16 Nov 2007 10:55:56 -0500, Tam/WB2TT wrote:


Remember, with cycle skipping the frequency changes. At 10 percent power the
fequency would be 6 Hertz.

The flicker will be 12 Hertz (as opposed to 120Hz at full power). You
don't have to skip whole cycles; half-cycles will do. The polarity doesn't
matter for a resistive load.

In extreme cases, I have seen incandescents visibly flicker from
skipping every other half cycle. The main example is a 4 watt or 7 watt
120V incandescent nightlight with a diode. The thin filament warms and
cools fast enough to have significant 60 Hz flicker. 60 Hz flicker is
sometimes visible.

- Don Klipstein (don@xxxxxxxxx)


Yes, you can't practically dim an incandescent bulb by skipping
cycles. I tried it many years ago and the results were miserable.
Maybe if you had control over the bulb design and could add some
thermal mass to the filament, but I tried it with a huge incandescent
(kW, IIRC) and even that thick filament responded too fast. I used
some kind of clever (I thought) CMOS circuit (I forget the details)
using something like a rate multiplier to get a relatively fast cycle
time (eg. 50% would be a 30Hz cycle). OTOH, it worked a charm on
relatively fast-response heaters for tight temperature control, which
was the intended purpose.


Best regards,
Spehro Pefhany


The persistence of vision, the flicker frequencies for most folks is
about 8hz, so when the proportion f 1/2 cycle arpoaches that some folks
will begin to see it, and other will not, as you eat more cycles of
course the drive is more choppy and you cant average out the photons as
the other poster noted :-)

No, the "flicker fusion frequency" is more like 50-70Hz and the
motion fusion more like 25-30Hz. There is a reason movies selected
24fps (and use double or triple shuttered for 48 or 72Hz flicker) and
TV is 30fps (interlaced to 60fps) (NTSC).

But, you can conceptually make this dimmer and thats what the poster
wanted. The traditional and widely adopted intra-cycle modulation is
used everywhere.... Perhaps there is a space where you want one, maybe
one that can do both.. not sure?

Everywhere?

OTOH, one poster suggested that , using 1/2 cycle non symmetry would
result in a net DC component and that it was bad. Not sure what would
dbe bad on a light bulb load, with a slight, very tiny mathemical sized
DC component.. PLease advise what sort of effects you were envisioning??

It's not going to bother a resistive load, though for light bulbs the
classical Triac dimmer circuit works better.

--
Keith
.

Relevant Pages

  • Re: Light bulb power control/dimmer
    ... The flicker will be 12 Hertz. ... skipping every other half cycle. ... 120V incandescent nightlight with a diode. ...
    (sci.electronics.design)
  • Re: Light bulb power control/dimmer
    ... The flicker will be 12 Hertz. ... skipping every other half cycle. ... 120V incandescent nightlight with a diode. ... Maybe if you had control over the bulb design and could add some ...
    (sci.electronics.design)
  • Re: Light bulb power control/dimmer
    ... The flicker will be 12 Hertz. ... I have seen incandescents visibly flicker from ... skipping every other half cycle. ... Don Klipstein ...
    (sci.electronics.design)
  • Re: Light bulb power control/dimmer
    ... The flicker will be 12 Hertz. ... skipping every other half cycle. ... 120V incandescent nightlight with a diode. ...
    (sci.electronics.design)
  • Re: Light bulb power control/dimmer
    ... I have seen incandescents visibly flicker from skipping every other half cycle. ... The main example is a 4 watt or 7 watt 120V incandescent nightlight with a diode. ... Don Klipstein ...
    (sci.electronics.design)