Re: Making an X-10 lamp module immune to dimming

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"isw" <isw@xxxxxxxxxxx> wrote in message
news:isw-D9C27F.22374307062008@xxxxxxxxxxxxxxxxxxxxxxxxx
> In article <F7udnWa4cqAYo9fVnZ2dnUVZ_rCtnZ2d@xxxxxxx>,
>  "Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:
>
>
> --snip--
>
> > I am still a bit confused about one thing.  When the AC waveform crosses
> > over, does current through the device drop to zero and the triac stops
> > conducting simply because there's no current at that point on the sine
wave?
>
> Precisely.
>
> > Does the triac have to be "retriggered" at that point and after each
> > subsequent recrossing or does it start firing again as soon as current
> > begins to flow again in the opposite direction?
>
> It will not conduct again until the proper amount of gate current is
> applied, while there is a voltage across the device.
>
> > I have another question.  When taking apart the lamp module, I noticed
that
> > the tiny triac has an enormous aluminum heat sink.  What process
generates
> > the high heat developed?
>
> Mostly, it's the voltage drop across the chunk of silicon that forms the
> triac, although some of it may be due to the tiny wires that connect the
> chip to the external leads.
>
> A transistor is a three-layer device (NPN, say); a SCR is a four-layer
> device (NPNP), and a triac comprises five (NPNPN or the other way
> around). Interestingly, because of the way thyristors work, even though
> they have more layers than transistors, the voltage drop across one when
> conducting is lower.
>
> But still, whatever that drop is, multiplied by RMS current that is
> flowing, creates heat.
>
> If you think about it, the worst case is when the device is "half on",
> because the voltage drop is much larger. One reason to use a triac or
> SCR instead of a transistor is because they sort of "automatically" go
> through that halfway state very rapidly. Another is that the voltage
> drop when conducting is lower.

That explains a few things, especially why dimmers get very hot when dimming
at some levels but not others.  What I am trying to say is that the heat
output curve looks very unlike a resistive dimmer in the same circuit.

Thanks!

--
Bobby G.