Re: Controlling Holiday Lights

[sylvan butler <ZsdbUse1+noZs_0611@xxxxxxxxxxxxxxxxxxxxx>]

On Fri, 03 Nov 2006 23:27:48 -0500, Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, 3 Nov 2006 16:05:12 -0700, sylvan butler
><ZsdbUse1+noZs_0611@xxxxxxxxxxxxxxxxxxxxx> wrote in message
><slrneknip8.p3a.ZsdbUse1+noZs_0611@xxxxxxxxxxxxxxx>:
>>> would be doing is chopping the AC into really small chunks and they
>>> would average over the entire wave(s).
>>
>>that's pretty much how it would work.  But it is a lot easier with D.C.
>>You would have to be really motivated to do it with A.C.
>
> There you go again ;-)
>
> Powering lamps designed for 120VAC with rectified 170 VDC (= 170 VRMS) as you
> suggest is problematic because if the circuit were to ever stop chopping, the
> lamp would burn out right quick.

You misunderstand.

120vac sine wave == about +/-170v peak.  I was not suggesting creating a
filtered 170vdc supply, just rectifying the 120vac sine wave.

You won't need a chopper, because it isn't pure D.C. steady at 170v, it
is just the lower (negative going) half of the wave flopped into the
gaps on the top.  Still goes up to 170v and down to 0v, 120 times per
second, it just no longer alternates, hence it is D.C. (pulsating).

> So when MOSFETs are used as the dimming control elements for lamps with an AC
> power source, the lamps are powered by AC, *not* DC. (and the circuit is

So my Athlon 64 is powered by A.C. because I plug it into an A.C. power
source?  Sure, in some sense, but not practically correct.  Put a scope
on the power leads, the Athlon is definiteliy powered by D.C. and if you
rectify the incoming A.C., you no longer have A.C.

It is only A.C. if it alternates polarity.  That is what Alternating
Current means.

sdb
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